Apache Camel Development Guide
Develop applications with Apache Camel
Copyright © 2011-2015 Red Hat, Inc. and/or its affiliates.
Abstract
Part I. Implementing Enterprise Integration Patterns
Abstract
Chapter 1. Building Blocks for Route Definitions
Abstract
1.1. Implementing a RouteBuilder Class
Overview
RouteBuilder
class and override its configure()
method (where you define your routing rules).
RouteBuilder
classes as necessary. Each class is instantiated once and is registered with the CamelContext
object. Normally, the lifecycle of each RouteBuilder
object is managed automatically by the container in which you deploy the router.
RouteBuilder classes
RouteBuilder
classes. There are two alternative RouteBuilder
classes that you can inherit from:
org.apache.camel.builder.RouteBuilder
—this is the genericRouteBuilder
base class that is suitable for deploying into any container type. It is provided in thecamel-core
artifact.org.apache.camel.spring.SpringRouteBuilder
—this base class is specially adapted to the Spring container. In particular, it provides extra support for the following Spring specific features: looking up beans in the Spring registry (using thebeanRef()
Java DSL command) and transactions (see the Transactions Guide for details). It is provided in thecamel-spring
artifact.
RouteBuilder
class defines methods used to initiate your routing rules (for example, from()
, intercept()
, and exception()
).
Implementing a RouteBuilder
RouteBuilder
implementation. The configure()
method body contains a routing rule; each rule is a single Java statement.
Example 1.1. Implementation of a RouteBuilder Class
import org.apache.camel.builder.RouteBuilder; public class MyRouteBuilder extends RouteBuilder { public void configure() { // Define routing rules here: from("file:src/data?noop=true").to("file:target/messages"); // More rules can be included, in you like. // ... } }
from(URL1).to(URL2)
instructs the router to read files from the directory src/data
and send them to the directory target/messages
. The option ?noop=true
instructs the router to retain (not delete) the source files in the src/data
directory.
1.2. Basic Java DSL Syntax
What is a DSL?
command01; command02; command03;
command01().command02().command03()
command01().startBlock().command02().command03().endBlock()
Router rule syntax
RouteBuilder.configure()
implementation. Figure 1.1, “Local Routing Rules” shows an overview of the basic syntax for defining local routing rules.
Figure 1.1. Local Routing Rules
from("EndpointURL")
method, which specifies the source of messages (consumer endpoint) for the routing rule. You can then add an arbitrarily long chain of processors to the rule (for example, filter()
). You typically finish off the rule with a to("EndpointURL")
method, which specifies the target (producer endpoint) for the messages that pass through the rule. However, it is not always necessary to end a rule with to()
. There are alternative ways of specifying the message target in a rule.
intercept()
, exception()
, or errorHandler()
). Global rules are outside the scope of this guide.
Consumers and producers
from("EndpointURL")
, and typically (but not always) ends by defining a producer endpoint, using to("EndpointURL")
. The endpoint URLs, EndpointURL, can use any of the components configured at deploy time. For example, you could use a file endpoint, file:MyMessageDirectory
, an Apache CXF endpoint, cxf:MyServiceName
, or an Apache ActiveMQ endpoint, activemq:queue:MyQName
. For a complete list of component types, see "Apache Camel Component Reference".
Exchanges
- In message—is the current message encapsulated by the exchange. As the exchange progresses through a route, this message may be modified. So the In message at the start of a route is typically not the same as the In message at the end of the route. The
org.apache.camel.Message
type provides a generic model of a message, with the following parts:- Body.
- Headers.
- Attachments.
It is important to realize that this is a generic model of a message. Apache Camel supports a large variety of protocols and endpoint types. Hence, it is not possible to standardize the format of the message body or the message headers. For example, the body of a JMS message would have a completely different format to the body of a HTTP message or a Web services message. For this reason, the body and the headers are declared to be ofObject
type. The original content of the body and the headers is then determined by the endpoint that created the exchange instance (that is, the endpoint appearing in thefrom()
command). - Out message—is a temporary holding area for a reply message or for a transformed message. Certain processing nodes (in particular, the
to()
command) can modify the current message by treating the In message as a request, sending it to a producer endpoint, and then receiving a reply from that endpoint. The reply message is then inserted into the Out message slot in the exchange.Normally, if an Out message has been set by the current node, Apache Camel modifies the exchange as follows before passing it to the next node in the route: the old In message is discarded and the Out message is moved to the In message slot. Thus, the reply becomes the new current message. For a more detailed discussion of how Apache Camel connects nodes together in a route, see Section 2.1, “Pipeline Processing”.There is one special case where an Out message is treated differently, however. If the consumer endpoint at the start of a route is expecting a reply message, the Out message at the very end of the route is taken to be the consumer endpoint's reply message (and, what is more, in this case the final node must create an Out message or the consumer endpoint would hang) . - Message exchange pattern (MEP)—affects the interaction between the exchange and endpoints in the route, as follows:
- Consumer endpoint—the consumer endpoint that creates the original exchange sets the initial value of the MEP. The initial value indicates whether the consumer endpoint expects to receive a reply (for example, the InOut MEP) or not (for example, the InOnly MEP).
- Producer endpoints—the MEP affects the producer endpoints that the exchange encounters along the route (for example, when an exchange passes through a
to()
node). For example, if the current MEP is InOnly, ato()
node would not expect to receive a reply from the endpoint. Sometimes you need to change the current MEP in order to customize the exchange's interaction with a producer endpoint. For more details, see Section 1.4, “Endpoints”.
- Exchange properties—a list of named properties containing metadata for the current message.
Message exchange patterns
Exchange
object makes it easy to generalize message processing to different message exchange patterns. For example, an asynchronous protocol might define an MEP that consists of a single message that flows from the consumer endpoint to the producer endpoint (an InOnly MEP). An RPC protocol, on the other hand, might define an MEP that consists of a request message and a reply message (an InOut MEP). Currently, Apache Camel supports the following MEPs:
InOnly
RobustInOnly
InOut
InOptionalOut
OutOnly
RobustOutOnly
OutIn
OutOptionalIn
org.apache.camel.ExchangePattern
.
Grouped exchanges
java.util.List
of Exchange
objects stored in the Exchange.GROUPED_EXCHANGE
exchange property. For an example of how to use grouped exchanges, see Section 8.5, “Aggregator”.
Processors
filter()
processor that takes an xpath()
predicate as its argument.
Expressions and predicates
foo
header is equal to the value bar
:
from("seda:a").filter(header("foo").isEqualTo("bar")).to("seda:b");
header("foo").isEqualTo("bar")
. To construct more sophisticated predicates and expressions, based on the message content, you can use one of the expression and predicate languages (see Expression and Predicate Languages).
1.3. Router Schema in a Spring XML File
Namespace
http://camel.apache.org/schema/spring
Specifying the schema location
http://camel.apache.org/schema/spring/camel-spring.xsd
, which references the latest version of the schema on the Apache Web site. For example, the root beans
element of an Apache Camel Spring file is normally configured as shown in Example 1.2, “ Specifying the Router Schema Location”.
Example 1.2. Specifying the Router Schema Location
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:camel="http://camel.apache.org/schema/spring"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd">
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
<!-- Define your routing rules here -->
</camelContext>
</beans>
Runtime schema location
camel-spring
JAR file. This ensures that the version of the schema used to parse the Spring file always matches the current runtime version. This is important, because the latest version of the schema posted up on the Apache Web site might not match the version of the runtime you are currently using.
Using an XML editor
xsi:schemaLocation
attribute. In order to be sure you are using the correct schema version whilst editing, it is usually a good idea to select a specific version of the camel-spring.xsd
file. For example, to edit a Spring file for the 2.3 version of Apache Camel, you could modify the beans element as follows:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:camel="http://camel.apache.org/schema/spring"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring-2.3.0.xsd">
...
camel-spring.xsd
, when you are finished editing. To see which schema versions are currently available for download, navigate to the Web page, http://camel.apache.org/schema/spring.
1.4. Endpoints
Overview
Endpoint URIs
scheme:contextPath[?queryOptions]
http
, and the contextPath provides URI details that are interpreted by the protocol. In addition, most schemes allow you to define query options, queryOptions, which are specified in the following format:
?option01=value01&option02=value02&...
http://www.google.com
C:\temp\src\data
directory:
file://C:/temp/src/data
timer://tickTock?period=1000
Working with Long Endpoint URIs
- Configure Endpoints Separately
- You can configure the endpoint separately, and from the routes refer to the endpoints using their shorthand IDs.
<camelContext ...> <endpoint id="foo" uri="ftp://foo@myserver"> <property name="password" value="secret"/> <property name="recursive" value="true"/> <property name="ftpClient.dataTimeout" value="30000"/> <property name="ftpClient.serverLanguageCode" value="fr"/> </endpoint> <route> <from uri="ref:foo"/> ... </route> </camelContext>
You can also configure some options in the URI and then use theproperty
attribute to specify additional options (or to override options from the URI).<endpoint id="foo" uri="ftp://foo@myserver?recursive=true"> <property name="password" value="secret"/> <property name="ftpClient.dataTimeout" value="30000"/> <property name="ftpClient.serverLanguageCode" value="fr"/> </endpoint>
- Split Endpoint Configuration Across New Lines
- You can split URI attributes using new lines.
<route> <from uri="ftp://foo@myserver?password=secret& recursive=true&ftpClient.dataTimeout=30000& ftpClientConfig.serverLanguageCode=fr"/> <to uri="bean:doSomething"/> </route>
NoteYou can specify one or more options on each line, each separated by&
.
Specifying time periods in a URI
[NHour(h|hour)][NMin(m|minute)][NSec(s|second)]
[]
, is optional and the notation, (A|B)
, indicates that A
and B
are alternatives.
timer
endpoint with a 45 minute period as follows:
from("timer:foo?period=45m") .to("log:foo");
from("timer:foo?period=1h15m") .to("log:foo"); from("timer:bar?period=2h30s") .to("log:bar"); from("timer:bar?period=3h45m58s") .to("log:bar");
Specifying raw values in URI options
RAW(RawValue)
. For example,
from("SourceURI")
.to("ftp:joe@myftpserver.com?password=RAW(se+re?t&23)&binary=true")
se+re?t&23
.
Case-insensitive enum options
enum
constants. For example, the level
option of the Log component, which can take the enum
values, INFO
, WARN
, ERROR
, and so on. This type conversion is case-insensitive, so any of the following alternatives could be used to set the logging level of a Log producer endpoint:
<to uri="log:foo?level=info"/> <to uri="log:foo?level=INfo"/> <to uri="log:foo?level=InFo"/>
Apache Camel components
<!-- Maven POM File --> <properties> <camel-version>2.15.1.redhat-620133</camel-version> ... </properties> <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-http</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
camel-core
artifact), so they are always available:
- Bean
- Browse
- Dataset
- Direct
- File
- Log
- Mock
- Properties
- Ref
- SEDA
- Timer
- VM
Consumer endpoints
from()
DSL command). In other words, the consumer endpoint is responsible for initiating processing in a route: it creates a new exchange instance (typically, based on some message that it has received or obtained), and provides a thread to process the exchange in the rest of the route.
payments
queue and processes them in the route:
from("jms:queue:payments") .process(SomeProcessor) .to("TargetURI");
<camelContext id="CamelContextID" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="jms:queue:payments"/> <process ref="someProcessorId"/> <to uri="TargetURI"/> </route> </camelContext>
from("quartz://secondTimer?trigger.repeatInterval=1000") .process(SomeProcessor) .to("TargetURI");
fromF()
Java DSL command. For example, to substitute the username and password into the URI for an FTP endpoint, you could write the route in Java, as follows:
fromF("ftp:%s@fusesource.com?password=%s", username, password) .process(SomeProcessor) .to("TargetURI");
%s
is replaced by the value of the username
string and the second occurrence of %s
is replaced by the password
string. This string formatting mechanism is implemented by String.format()
and is similar to the formatting provided by the C printf()
function. For details, see java.util.Formatter.
Producer endpoints
to()
DSL command). In other words, the producer endpoint receives an existing exchange object and sends the contents of the exchange to the specified endpoint.
from("SourceURI") .process(SomeProcessor) .to("jms:queue:orderForms");
<camelContext id="CamelContextID" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURI"/> <process ref="someProcessorId"/> <to uri="jms:queue:orderForms"/> </route> </camelContext>
from("SourceURI") .process(SomeProcessor) .to("http://www.google.com/search?hl=en&q=camel+router");
toF()
Java DSL command. For example, to substitute a custom Google query into the HTTP URI, you could write the route in Java, as follows:
from("SourceURI") .process(SomeProcessor) .toF("http://www.google.com/search?hl=en&q=%s", myGoogleQuery);
%s
is replaced by your custom query string, myGoogleQuery
. For details, see java.util.Formatter.
1.5. Processors
Overview
Java DSL | XML DSL | Description |
---|---|---|
aggregate() | aggregate |
Aggregator EIP: Creates an aggregator, which combines multiple incoming exchanges into a single exchange.
|
bean() , beanRef() | bean |
Process the current exchange by invoking a method on a Java object (or bean). See Section 2.4, “Bean Integration”.
|
choice() | choice |
Content Based Router EIP: Selects a particular sub-route based on the exchange content, using
when and otherwise clauses.
|
convertBodyTo() | convertBodyTo |
Converts the In message body to the specified type.
|
delay() | delay |
Delayer EIP: Delays the propagation of the exchange to the latter part of the route.
|
doTry() | doTry |
Creates a try/catch block for handling exceptions, using
doCatch , doFinally , and end clauses.
|
end() | N/A | Ends the current command block. |
enrich() ,enrichRef() | enrich |
Content Enricher EIP: Combines the current exchange with data requested from a specified producer endpoint URI.
|
filter() | filter |
Message Filter EIP: Uses a predicate expression to filter incoming exchanges.
|
idempotentConsumer() | idempotentConsumer |
Idempotent Consumer EIP: Implements a strategy to suppress duplicate messages.
|
inheritErrorHandler() | @inheritErrorHandler | Boolean option that can be used to disable the inherited error handler on a particular route node (defined as a sub-clause in the Java DSL and as an attribute in the XML DSL). |
inOnly() | inOnly |
Either sets the current exchange's MEP to InOnly (if no arguments) or sends the exchange as an InOnly to the specified endpoint(s).
|
inOut() | inOut |
Either sets the current exchange's MEP to InOut (if no arguments) or sends the exchange as an InOut to the specified endpoint(s).
|
loadBalance() | loadBalance |
Load Balancer EIP: Implements load balancing over a collection of endpoints.
|
log() | log | Logs a message to the console. |
loop() | loop |
Loop EIP: Repeatedly resends each exchange to the latter part of the route.
|
markRollbackOnly() | @markRollbackOnly | (Transactions) Marks the current transaction for rollback only (no exception is raised). In the XML DSL, this option is set as a boolean attribute on the rollback element. See "Transaction Guide". |
markRollbackOnlyLast() | @markRollbackOnlyLast | (Transactions) If one or more transactions have previously been associated with this thread and then suspended, this command marks the latest transaction for rollback only (no exception is raised). In the XML DSL, this option is set as a boolean attribute on the rollback element. See "Transaction Guide". |
marshal() | marshal |
Transforms into a low-level or binary format using the specified data format, in preparation for sending over a particular transport protocol.
|
multicast() | multicast |
Multicast EIP: Multicasts the current exchange to multiple destinations, where each destination gets its own copy of the exchange.
|
onCompletion() | onCompletion |
Defines a sub-route (terminated by
end() in the Java DSL) that gets executed after the main route has completed. For conditional execution, use the onWhen sub-clause. Can also be defined on its own line (not in a route).
|
onException() | onException |
Defines a sub-route (terminated by
end() in the Java DSL) that gets executed whenever the specified exception occurs. Usually defined on its own line (not in a route).
|
pipeline() | pipeline |
Pipes and Filters EIP: Sends the exchange to a series of endpoints, where the output of one endpoint becomes the input of the next endpoint. See also Section 2.1, “Pipeline Processing”.
|
policy() | policy |
Apply a policy to the current route (currently only used for transactional policies—see "Transaction Guide").
|
pollEnrich() ,pollEnrichRef() | pollEnrich |
Content Enricher EIP: Combines the current exchange with data polled from a specified consumer endpoint URI.
|
process() ,processRef | process |
Execute a custom processor on the current exchange. See the section called “Custom processor” and Part IV, “Programming EIP Components”.
|
recipientList() | recipientList |
Recipient List EIP: Sends the exchange to a list of recipients that is calculated at runtime (for example, based on the contents of a header).
|
removeHeader() | removeHeader |
Removes the specified header from the exchange's In message.
|
removeHeaders() | removeHeaders | Removes the headers matching the specified pattern from the exchange's In message. The pattern can have the form, prefix* —in which case it matches every name starting with prefix—otherwise, it is interpreted as a regular expression. |
removeProperty() | removeProperty |
Removes the specified exchange property from the exchange.
|
removeProperties() | removeProperties |
Removes the properties matching the specified pattern from the exchange. Takes a comma separated list of 1 or more strings as arguments. The first string is the pattern (see
removeHeaders() above). Subsequent strings specify exceptions - these properties remain.
|
resequence() | resequence |
Resequencer EIP: Re-orders incoming exchanges on the basis of a specified comparotor operation. Supports a batch mode and a stream mode.
|
rollback() | rollback |
(Transactions) Marks the current transaction for rollback only (also raising an exception, by default). See "Transaction Guide".
|
routingSlip() | routingSlip |
Routing Slip EIP: Routes the exchange through a pipeline that is constructed dynamically, based on the list of endpoint URIs extracted from a slip header.
|
sample() | sample | Creates a sampling throttler, allowing you to extract a sample of exchanges from the traffic on a route. |
setBody() | setBody |
Sets the message body of the exchange's In message.
|
setExchangePattern() | setExchangePattern |
Sets the current exchange's MEP to the specified value. See the section called “Message exchange patterns”.
|
setHeader() | setHeader |
Sets the specified header in the exchange's In message.
|
setOutHeader() | setOutHeader |
Sets the specified header in the exchange's Out message.
|
setProperty() | setProperty() |
Sets the specified exchange property.
|
sort() | sort |
Sorts the contents of the In message body (where a custom comparator can optionally be specified).
|
split() | split |
Splitter EIP: Splits the current exchange into a sequence of exchanges, where each split exchange contains a fragment of the original message body.
|
stop() | stop |
Stops routing the current exchange and marks it as completed.
|
threads() | threads |
Creates a thread pool for concurrent processing of the latter part of the route.
|
throttle() | throttle |
Throttler EIP: Limit the flow rate to the specified level (exchanges per second).
|
throwException() | throwException |
Throw the specified Java exception.
|
to() | to |
Send the exchange to one or more endpoints. See Section 2.1, “Pipeline Processing”.
|
toF() | N/A | Send the exchange to an endpoint, using string formatting. That is, the endpoint URI string can embed substitutions in the style of the C printf() function. |
transacted() | transacted |
Create a Spring transaction scope that encloses the latter part of the route. See "Transaction Guide".
|
transform() | transform |
Message Translator EIP: Copy the In message headers to the Out message headers and set the Out message body to the specified value.
|
unmarshal() | unmarshal |
Transforms the In message body from a low-level or binary format to a high-level format, using the specified data format.
|
validate() | validate | Takes a predicate expression to test whether the current message is valid. If the predicate returns false , throws a PredicateValidationException exception. |
wireTap() | wireTap |
Wire Tap EIP: Sends a copy of the current exchange to the specified wire tap URI, using the
ExchangePattern.InOnly MEP.
|
Some sample processors
Choice
choice()
processor is a conditional statement that is used to route incoming messages to alternative producer endpoints. Each alternative producer endpoint is preceded by a when()
method, which takes a predicate argument. If the predicate is true, the following target is selected, otherwise processing proceeds to the next when()
method in the rule. For example, the following choice()
processor directs incoming messages to either Target1, Target2, or Target3, depending on the values of Predicate1 and Predicate2:
from("SourceURL") .choice() .when(Predicate1).to("Target1") .when(Predicate2).to("Target2") .otherwise().to("Target3");
<camelContext id="buildSimpleRouteWithChoice" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURL"/> <choice> <when> <!-- First predicate --> <simple>header.foo = 'bar'</simple> <to uri="Target1"/> </when> <when> <!-- Second predicate --> <simple>header.foo = 'manchu'</simple> <to uri="Target2"/> </when> <otherwise> <to uri="Target3"/> </otherwise> </choice> </route> </camelContext>
endChoice()
command. Some of the standard Apache Camel processors enable you to specify extra parameters using special sub-clauses, effectively opening an extra level of nesting which is usually terminated by the end()
command. For example, you could specify a load balancer clause as loadBalance().roundRobin().to("mock:foo").to("mock:bar").end()
, which load balances messages between the mock:foo
and mock:bar
endpoints. If the load balancer clause is embedded in a choice condition, however, it is necessary to terminate the clause using the endChoice()
command, as follows:
from("direct:start") .choice() .when(bodyAs(String.class).contains("Camel")) .loadBalance().roundRobin().to("mock:foo").to("mock:bar").endChoice() .otherwise() .to("mock:result");
Filter
filter()
processor can be used to prevent uninteresting messages from reaching the producer endpoint. It takes a single predicate argument: if the predicate is true, the message exchange is allowed through to the producer; if the predicate is false, the message exchange is blocked. For example, the following filter blocks a message exchange, unless the incoming message contains a header, foo
, with value equal to bar
:
from("SourceURL").filter(header("foo").isEqualTo("bar")).to("TargetURL");
<camelContext id="filterRoute" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURL"/> <filter> <simple>header.foo = 'bar'</simple> <to uri="TargetURL"/> </filter> </route> </camelContext>
Throttler
throttle()
processor ensures that a producer endpoint does not get overloaded. The throttler works by limiting the number of messages that can pass through per second. If the incoming messages exceed the specified rate, the throttler accumulates excess messages in a buffer and transmits them more slowly to the producer endpoint. For example, to limit the rate of throughput to 100 messages per second, you can define the following rule:
from("SourceURL").throttle(100).to("TargetURL");
<camelContext id="throttleRoute" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURL"/> <throttle maximumRequestsPerPeriod="100" timePeriodMillis="1000"> <to uri="TargetURL"/> </throttle> </route> </camelContext>
Custom processor
org.apache.camel.Processor
interface and overrides the process()
method. The following custom processor, MyProcessor
, removes the header named foo
from incoming messages:
Example 1.3. Implementing a Custom Processor Class
public class MyProcessor implements org.apache.camel.Processor { public void process(org.apache.camel.Exchange exchange) { inMessage = exchange.getIn(); if (inMessage != null) { inMessage.removeHeader("foo"); } } };
process()
method, which provides a generic mechanism for inserting processors into rules. For example, the following rule invokes the processor defined in Example 1.3, “Implementing a Custom Processor Class”:
org.apache.camel.Processor myProc = new MyProcessor(); from("SourceURL").process(myProc).to("TargetURL");
Chapter 2. Basic Principles of Route Building
Abstract
2.1. Pipeline Processing
Overview
ls | more
is an example of a command that pipes a directory listing, ls
, to the page-scrolling utility, more
. The basic idea of a pipeline is that the output of one command is fed into the input of the next. The natural analogy in the case of a route is for the Out message from one processor to be copied to the In message of the next processor.
Processor nodes
org.apache.camel.Processor
interface. In other words, processors make up the basic building blocks of a DSL route. For example, DSL commands such as filter()
, delayer()
, setBody()
, setHeader()
, and to()
all represent processors. When considering how processors connect together to build up a route, it is important to distinguish two different processing approaches.
null
in this case.
Figure 2.1. Processor Modifying an In Message
setHeader()
command that modifies the current In message by adding (or modifying) the BillingSystem
heading:
from("activemq:orderQueue") .setHeader("BillingSystem", xpath("/order/billingSystem")) .to("activemq:billingQueue");
Figure 2.2. Processor Creating an Out Message
transform()
command that creates an Out message with a message body containing the string, DummyBody
:
from("activemq:orderQueue") .transform(constant("DummyBody")) .to("activemq:billingQueue");
constant("DummyBody")
represents a constant expression. You cannot pass the string, DummyBody
, directly, because the argument to transform()
must be an expression type.
Pipeline for InOnly exchanges
Figure 2.3. Sample Pipeline for InOnly Exchanges
userdataQueue
queue, pipes the message through a Velocity template (to produce a customer address in text format), and then sends the resulting text address to the queue, envelopeAddressQueue
:
from("activemq:userdataQueue") .to(ExchangePattern.InOut, "velocity:file:AdressTemplate.vm") .to("activemq:envelopeAddresses");
velocity:file:AdressTemplate.vm
, specifies the location of a Velocity template file, file:AdressTemplate.vm
, in the file system. The to()
command changes the exchange pattern to InOut before sending the exchange to the Velocity endpoint and then changes it back to InOnly afterwards. For more details of the Velocity endpoint, see chapter "Velocity" in "Apache Camel Component Reference".
Pipeline for InOut exchanges
Figure 2.4. Sample Pipeline for InOut Exchanges
from("jetty:http://localhost:8080/foo") .to("cxf:bean:addAccountDetails") .to("cxf:bean:getCreditRating") .to("cxf:bean:processTransaction");
cxf:bean:addAccountDetails
, cxf:bean:getCreditRating
, and cxf:bean:processTransaction
. The final Web service, processTransaction
, generates a response (Out message) that is sent back through the JETTY endpoint.
from("jetty:http://localhost:8080/foo") .pipeline("cxf:bean:addAccountDetails", "cxf:bean:getCreditRating", "cxf:bean:processTransaction");
Pipeline for InOptionalOut exchanges
null
Out message is copied to the In message of the next node in the pipeline. By contrast, in the case of an InOut exchange, a null
Out message is discarded and the original In message from the current node would be copied to the In message of the next node instead.
2.2. Multiple Inputs
Overview
from(EndpointURL)
syntax in the Java DSL. But what if you need to define multiple inputs for your route? Apache Camel provides several alternatives for specifying multiple inputs to a route. The approach to take depends on whether you want the exchanges to be processed independently of each other or whether you want the exchanges from different inputs to be combined in some way (in which case, you should use the the section called “Content enricher pattern”).
Multiple independent inputs
from()
DSL command, for example:
from("URI1", "URI2", "URI3").to("DestinationUri");
from("URI1").from("URI2").from("URI3").to("DestinationUri");
from("URI1").to("DestinationUri"); from("URI2").to("DestinationUri"); from("URI3").to("DestinationUri");
Segmented routes
Figure 2.5. Processing Multiple Inputs with Segmented Routes
activemq:Nyse
and activemq:Nasdaq
—and send the incoming exchanges to an internal endpoint, InternalUrl. The second route segment merges the incoming exchanges, taking them from the internal endpoint and sending them to the destination queue, activemq:USTxn
. The InternalUrl is the URL for an endpoint that is intended only for use within a router application. The following types of endpoints are suitable for internal use:
Direct endpoints
direct:EndpointID
, where the endpoint ID, EndpointID, is simply a unique alphanumeric string that identifies the endpoint instance.
activemq:Nyse
and activemq:Nasdaq
, and merge them into a single message queue, activemq:USTxn
, you can do this by defining the following set of routes:
from("activemq:Nyse").to("direct:mergeTxns"); from("activemq:Nasdaq").to("direct:mergeTxns"); from("direct:mergeTxns").to("activemq:USTxn");
Nyse
and Nasdaq
, and send them to the endpoint, direct:mergeTxns
. The last queue combines the inputs from the previous two queues and sends the combined message stream to the activemq:USTxn
queue.
to("direct:mergeTxns")
), the direct endpoint passes the exchange directly to all of the consumers endpoints that have the same endpoint ID (for example, from("direct:mergeTxns")
). Direct endpoints can only be used to communicate between routes that belong to the same CamelContext
in the same Java virtual machine (JVM) instance.
SEDA endpoints
- Processing of a SEDA endpoint is not synchronous. That is, when you send an exchange to a SEDA producer endpoint, control immediately returns to the preceding processor in the route.
- SEDA endpoints contain a queue buffer (of
java.util.concurrent.BlockingQueue
type), which stores all of the incoming exchanges prior to processing by the next route segment. - Each SEDA consumer endpoint creates a thread pool (the default size is 5) to process exchange objects from the blocking queue.
- The SEDA component supports the competing consumers pattern, which guarantees that each incoming exchange is processed only once, even if there are multiple consumers attached to a specific endpoint.
from("activemq:Nyse").to("seda:mergeTxns"); from("activemq:Nasdaq").to("seda:mergeTxns"); from("seda:mergeTxns").to("activemq:USTxn");
seda:mergeTxns
to activemq:USTxn
) is processed by a pool of five threads.
VM endpoints
CamelContext
, the VM component enables you to link together routes from distinct Apache Camel applications, as long as they are running within the same Java virtual machine.
from("activemq:Nyse").to("vm:mergeTxns"); from("activemq:Nasdaq").to("vm:mergeTxns");
from("vm:mergeTxns").to("activemq:USTxn");
Content enricher pattern
src/data/ratings
. You can combine the incoming credit request with data from the ratings file using the pollEnrich()
pattern and a GroupedExchangeAggregationStrategy
aggregation strategy, as follows:
from("jms:queue:creditRequests") .pollEnrich("file:src/data/ratings?noop=true", new GroupedExchangeAggregationStrategy()) .bean(new MergeCreditRequestAndRatings(), "merge") .to("jms:queue:reformattedRequests");
GroupedExchangeAggregationStrategy
class is a standard aggregation strategy from the org.apache.camel.processor.aggregate
package that adds each new exchange to a java.util.List
instance and stores the resulting list in the Exchange.GROUPED_EXCHANGE
exchange property. In this case, the list contains two elements: the original exchange (from the creditRequests
JMS queue); and the enricher exchange (from the file endpoint).
public class MergeCreditRequestAndRatings {
public void merge(Exchange ex) {
// Obtain the grouped exchange
List<Exchange> list = ex.getProperty(Exchange.GROUPED_EXCHANGE
, List.class);
// Get the exchanges from the grouped exchange
Exchange originalEx = list.get(0);
Exchange ratingsEx = list.get(1);
// Merge the exchanges
...
}
}
2.3. Exception Handling
Abstract
doTry
, doCatch
, and doFinally
; or you can specify what action to take for each exception type and apply this rule to all routes in a RouteBuilder
using onException
; or you can specify what action to take for all exception types and apply this rule to all routes in a RouteBuilder
using errorHandler
.
2.3.1. onException Clause
Overview
onException
clause is a powerful mechanism for trapping exceptions that occur in one or more routes: it is type-specific, enabling you to define distinct actions to handle different exception types; it allows you to define actions using essentially the same (actually, slightly extended) syntax as a route, giving you considerable flexibility in the way you handle exceptions; and it is based on a trapping model, which enables a single onException
clause to deal with exceptions occurring at any node in any route.
Trapping exceptions using onException
onException
clause is a mechanism for trapping, rather than catching exceptions. That is, once you define an onException
clause, it traps exceptions that occur at any point in a route. This contrasts with the Java try/catch mechanism, where an exception is caught, only if a particular code fragment is explicitly enclosed in a try block.
onException
clause is that the Apache Camel runtime implicitly encloses each route node in a try block. This is why the onException
clause is able to trap exceptions at any point in the route. But this wrapping is done for you automatically; it is not visible in the route definitions.
Java DSL example
onException
clause applies to all of the routes defined in the RouteBuilder
class. If a ValidationException
exception occurs while processing either of the routes (from("seda:inputA")
or from("seda:inputB")
), the onException
clause traps the exception and redirects the current exchange to the validationFailed
JMS queue (which serves as a deadletter queue).
// Java public class MyRouteBuilder extends RouteBuilder { public void configure() { onException(ValidationException.class) .to("activemq:validationFailed"); from("seda:inputA") .to("validation:foo/bar.xsd", "activemq:someQueue"); from("seda:inputB").to("direct:foo") .to("rnc:mySchema.rnc", "activemq:anotherQueue"); } }
XML DSL example
onException
element to define the exception clause, as follows:
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:camel="http://camel.apache.org/schema/spring" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd"> <camelContext xmlns="http://camel.apache.org/schema/spring"> <onException> <exception>com.mycompany.ValidationException</exception> <to uri="activemq:validationFailed"/> </onException> <route> <from uri="seda:inputA"/> <to uri="validation:foo/bar.xsd"/> <to uri="activemq:someQueue"/> </route> <route> <from uri="seda:inputB"/> <to uri="rnc:mySchema.rnc"/> <to uri="activemq:anotherQueue"/> </route> </camelContext> </beans>
Trapping multiple exceptions
onException
clauses to trap exceptions in a RouteBuilder
scope. This enables you to take different actions in response to different exceptions. For example, the following series of onException
clauses defined in the Java DSL define different deadletter destinations for ValidationException
, ValidationException
, and Exception
:
onException(ValidationException.class).to("activemq:validationFailed"); onException(java.io.IOException.class).to("activemq:ioExceptions"); onException(Exception.class).to("activemq:exceptions");
onException
clauses in the XML DSL as follows:
<onException> <exception>com.mycompany.ValidationException</exception> <to uri="activemq:validationFailed"/> </onException> <onException> <exception>java.io.IOException</exception> <to uri="activemq:ioExceptions"/> </onException> <onException> <exception>java.lang.Exception</exception> <to uri="activemq:exceptions"/> </onException>
onException
clause. In the Java DSL, you can group multiple exceptions as follows:
onException(ValidationException.class, BuesinessException.class) .to("activemq:validationFailed");
exception
element inside the onException
element, as follows:
<onException> <exception>com.mycompany.ValidationException</exception> <exception>com.mycompany.BuesinessException</exception> <to uri="activemq:validationFailed"/> </onException>
onException
clauses is significant. Apache Camel initially attempts to match the thrown exception against the first clause. If the first clause fails to match, the next onException
clause is tried, and so on until a match is found. Each matching attempt is governed by the following algorithm:
- If the thrown exception is a chained exception (that is, where an exception has been caught and rethrown as a different exception), the most nested exception type serves initially as the basis for matching. This exception is tested as follows:
- If the exception-to-test has exactly the type specified in the
onException
clause (tested usinginstanceof
), a match is triggered. - If the exception-to-test is a sub-type of the type specified in the
onException
clause, a match is triggered.
- If the most nested exception fails to yield a match, the next exception in the chain (the wrapping exception) is tested instead. The testing continues up the chain until either a match is triggered or the chain is exhausted.
Deadletter channel
onException
usage have so far all exploited the deadletter channel pattern. That is, when an onException
clause traps an exception, the current exchange is routed to a special destination (the deadletter channel). The deadletter channel serves as a holding area for failed messages that have not been processed. An administrator can inspect the messages at a later time and decide what action needs to be taken.
Use original message
useOriginalMessage()
DSL command, as follows:
onException(ValidationException.class) .useOriginalMessage() .to("activemq:validationFailed");
useOriginalMessage
attribute on the onException
element, as follows:
<onException useOriginalMessage="true"> <exception>com.mycompany.ValidationException</exception> <to uri="activemq:validationFailed"/> </onException>
useOriginalMessage()
. But if the setAllowUseOriginalMessage()
option is set to false
on the Camel context, the original message will not be accessible and you cannot call useOriginalMessage()
(for example, you might want to choose this behaviour to optimize performance when processing large messages).
Redelivery policy
-
maximumRedeliveries()
- Specifies the maximum number of times redelivery can be attempted (default is
0
). A negative value means redelivery is always attempted (equivalent to an infinite value). -
retryWhile()
- Specifies a predicate (of
Predicate
type), which determines whether Apache Camel ought to continue redelivering. If the predicate evaluates totrue
on the current exchange, redelivery is attempted; otherwise, redelivery is stopped and no further redelivery attempts are made.This option takes precedence over themaximumRedeliveries()
option.
onException
clause. For example, you can specify a maximum of six redeliveries, after which the exchange is sent to the validationFailed
deadletter queue, as follows:
onException(ValidationException.class) .maximumRedeliveries(6) .retryAttemptedLogLevel(org.apache.camel.LogginLevel.WARN) .to("activemq:validationFailed");
redeliveryPolicy
element. For example, the preceding route can be expressed in XML DSL as follows:
<onException useOriginalMessage="true"> <exception>com.mycompany.ValidationException</exception> <redeliveryPolicy maximumRedeliveries="6"/> <to uri="activemq:validationFailed"/> </onException>
redeliveryPolicyProfile
instance. You can then reference the redeliveryPolicyProfile
instance using the onException
element's redeliverPolicyRef
attribute. For example, the preceding route can be expressed as follows:
<redeliveryPolicyProfile id="redelivPolicy" maximumRedeliveries="6" retryAttemptedLogLevel="WARN"/> <onException useOriginalMessage="true" redeliveryPolicyRef="redelivPolicy"> <exception>com.mycompany.ValidationException</exception> <to uri="activemq:validationFailed"/> </onException>
redeliveryPolicyProfile
is useful, if you want to re-use the same redelivery policy in multiple onException
clauses.
Conditional trapping
onException
can be made conditional by specifying the onWhen
option. If you specify the onWhen
option in an onException
clause, a match is triggered only when the thrown exception matches the clause and the onWhen
predicate evaluates to true
on the current exchange.
onException
clause triggers, only if the thrown exception matches MyUserException
and the user
header is non-null in the current exchange:
// Java // Here we define onException() to catch MyUserException when // there is a header[user] on the exchange that is not null onException(MyUserException.class) .onWhen(header("user").isNotNull()) .maximumRedeliveries(2) .to(ERROR_USER_QUEUE); // Here we define onException to catch MyUserException as a kind // of fallback when the above did not match. // Noitce: The order how we have defined these onException is // important as Camel will resolve in the same order as they // have been defined onException(MyUserException.class) .maximumRedeliveries(2) .to(ERROR_QUEUE);
onException
clauses can be expressed in the XML DSL as follows:
<redeliveryPolicyProfile id="twoRedeliveries" maximumRedeliveries="2"/> <onException redeliveryPolicyRef="twoRedeliveries"> <exception>com.mycompany.MyUserException</exception> <onWhen> <simple>${header.user} != null</simple> </onWhen> <to uri="activemq:error_user_queue"/> </onException> <onException redeliveryPolicyRef="twoRedeliveries"> <exception>com.mycompany.MyUserException</exception> <to uri="activemq:error_queue"/> </onException>
Handling exceptions
onException
clause is triggered, the behavior is essentially the same, except that the onException
clause performs some processing before the thrown exception is propagated back.
onException
provides various options to modify the exception handling behavior, as follows:
- the section called “Suppressing exception rethrow”—you have the option of suppressing the rethrown exception after the
onException
clause has completed. In other words, in this case the exception does not propagate back to the consumer endpoint at the start of the route. - the section called “Continuing processing”—you have the option of resuming normal processing of the exchange from the point where the exception originally occurred. Implicitly, this approach also suppresses the rethrown exception.
- the section called “Sending a response”—in the special case where the consumer endpoint at the start of the route expects a reply (that is, having an InOut MEP), you might prefer to construct a custom fault reply message, rather than propagating the exception back to the consumer endpoint.
Suppressing exception rethrow
handled()
option to true
in the Java DSL, as follows:
onException(ValidationException.class) .handled(true) .to("activemq:validationFailed");
handled()
option can be of boolean type, of Predicate
type, or of Expression
type (where any non-boolean expression is interpreted as true
, if it evaluates to a non-null value).
handled
element, as follows:
<onException> <exception>com.mycompany.ValidationException</exception> <handled> <constant>true</constant> </handled> <to uri="activemq:validationFailed"/> </onException>
Continuing processing
continued
option to true
in the Java DSL, as follows:
onException(ValidationException.class) .continued(true);
continued()
option can be of boolean type, of Predicate
type, or of Expression
type (where any non-boolean expression is interpreted as true
, if it evaluates to a non-null value).
continued
element, as follows:
<onException> <exception>com.mycompany.ValidationException</exception> <continued> <constant>true</constant> </continued> </onException>
Sending a response
handled
option; and populate the exchange's Out message slot with a custom fault message.
Sorry
, whenever the MyFunctionalException
exception occurs:
// we catch MyFunctionalException and want to mark it as handled (= no failure returned to client) // but we want to return a fixed text response, so we transform OUT body as Sorry. onException(MyFunctionalException.class) .handled(true) .transform().constant("Sorry");
exceptionMessage()
builder method. For example, you can send a reply containing just the text of the exception message whenever the MyFunctionalException
exception occurs, as follows:
// we catch MyFunctionalException and want to mark it as handled (= no failure returned to client) // but we want to return a fixed text response, so we transform OUT body and return the exception message onException(MyFunctionalException.class) .handled(true) .transform(exceptionMessage());
exception.message
variable. For example, you could embed the current exception text in a reply message, as follows:
// we catch MyFunctionalException and want to mark it as handled (= no failure returned to client) // but we want to return a fixed text response, so we transform OUT body and return a nice message // using the simple language where we want insert the exception message onException(MyFunctionalException.class) .handled(true) .transform().simple("Error reported: ${exception.message} - cannot process this message.");
onException
clause can be expressed in XML DSL as follows:
<onException> <exception>com.mycompany.MyFunctionalException</exception> <handled> <constant>true</constant> </handled> <transform> <simple>Error reported: ${exception.message} - cannot process this message.</simple> </transform> </onException>
Exception thrown while handling an exception
onException
clause) is handled in a special way. Such an exception is handled by the special fallback exception handler, which handles the exception as follows:
- All existing exception handlers are ignored and processing fails immediately.
- The new exception is logged.
- The new exception is set on the exchange object.
onException
clause getting locked into an infinite loop.
Scopes
onException
clauses can be effective in either of the following scopes:
- RouteBuilder scope—
onException
clauses defined as standalone statements inside aRouteBuilder.configure()
method affect all of the routes defined in thatRouteBuilder
instance. On the other hand, theseonException
clauses have no effect whatsoever on routes defined inside any otherRouteBuilder
instance. TheonException
clauses must appear before the route definitions.All of the examples up to this point are defined using theRouteBuilder
scope. - Route scope—
onException
clauses can also be embedded directly within a route. These onException clauses affect only the route in which they are defined.
Route scope
onException
clause anywhere inside a route definition, but you must terminate the embedded onException
clause using the end()
DSL command.
onException
clause in the Java DSL, as follows:
// Java from("direct:start") .onException(OrderFailedException.class) .maximumRedeliveries(1) .handled(true) .beanRef("orderService", "orderFailed") .to("mock:error") .end() .beanRef("orderService", "handleOrder") .to("mock:result");
onException
clause in the XML DSL, as follows:
<route errorHandlerRef="deadLetter"> <from uri="direct:start"/> <onException> <exception>com.mycompany.OrderFailedException</exception> <redeliveryPolicy maximumRedeliveries="1"/> <handled> <constant>true</constant> </handled> <bean ref="orderService" method="orderFailed"/> <to uri="mock:error"/> </onException> <bean ref="orderService" method="handleOrder"/> <to uri="mock:result"/> </route>
2.3.2. Error Handler
Overview
errorHandler()
clause provides similar features to the onException
clause, except that this mechanism is not able to discriminate between different exception types. The errorHandler()
clause is the original exception handling mechanism provided by Apache Camel and was available before the onException
clause was implemented.
Java DSL example
errorHandler()
clause is defined in a RouteBuilder
class and applies to all of the routes in that RouteBuilder
class. It is triggered whenever an exception of any kind occurs in one of the applicable routes. For example, to define an error handler that routes all failed exchanges to the ActiveMQ deadLetter
queue, you can define a RouteBuilder
as follows:
public class MyRouteBuilder extends RouteBuilder { public void configure() { errorHandler(deadLetterChannel("activemq:deadLetter")); // The preceding error handler applies // to all of the following routes: from("activemq:orderQueue") .to("pop3://fulfillment@acme.com"); from("file:src/data?noop=true") .to("file:target/messages"); // ... } }
XML DSL example
camelContext
scope using the errorHandler
element. For example, to define an error handler that routes all failed exchanges to the ActiveMQ deadLetter
queue, you can define an errorHandler
element as follows:
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:camel="http://camel.apache.org/schema/spring" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd"> <camelContext xmlns="http://camel.apache.org/schema/spring"> <errorHandler type="DeadLetterChannel" deadLetterUri="activemq:deadLetter"/> <route> <from uri="activemq:orderQueue"/> <to uri="pop3://fulfillment@acme.com"/> </route> <route> <from uri="file:src/data?noop=true"/> <to uri="file:target/messages"/> </route> </camelContext> </beans>
Types of error handler
Java DSL Builder | XML DSL Type Attribute | Description |
---|---|---|
defaultErrorHandler() | DefaultErrorHandler | Propagates exceptions back to the caller and supports the redelivery policy, but it does not support a dead letter queue. |
deadLetterChannel() | DeadLetterChannel | Supports the same features as the default error handler and, in addition, supports a dead letter queue. |
loggingErrorChannel() | LoggingErrorChannel | Logs the exception text whenever an exception occurs. |
noErrorHandler() | NoErrorHandler | Dummy handler implementation that can be used to disable the error handler. |
TransactionErrorHandler | An error handler for transacted routes. A default transaction error handler instance is automatically used for a route that is marked as transacted. |
2.3.3. doTry, doCatch, and doFinally
Overview
doTry
, doCatch
, and doFinally
clauses, which handle exceptions in a similar way to Java's try
, catch
, and finally
blocks.
Similarities between doCatch and Java catch
doCatch()
clause in a route definition behaves in an analogous way to the catch()
statement in Java code. In particular, the following features are supported by the doCatch()
clause:
- Multiple doCatch clauses—you can have multiple
doCatch
clauses within a singledoTry
block. ThedoCatch
clauses are tested in the order they appear, just like Javacatch()
statements. Apache Camel executes the firstdoCatch
clause that matches the thrown exception.NoteThis algorithm is different from the exception matching algorithm used by theonException
clause—see Section 2.3.1, “onException Clause” for details. - Rethrowing exceptions—you can rethrow the current exception from within a
doCatch
clause using thehandled
sub-clause (see the section called “Rethrowing exceptions in doCatch”).
Special features of doCatch
doCatch()
clause, however, that have no analogue in the Java catch()
statement. The following features are specific to doCatch()
:
- Catching multiple exceptions—the
doCatch
clause allows you to specify a list of exceptions to catch, in contrast to the Javacatch()
statement, which catches only one exception (see the section called “Example”). - Conditional catching—you can catch an exception conditionally, by appending an
onWhen
sub-clause to thedoCatch
clause (see the section called “Conditional exception catching using onWhen”).
Example
doTry
block in the Java DSL, where the doCatch()
clause will be executed, if either the IOException
exception or the IllegalStateException
exception are raised, and the doFinally()
clause is always executed, irrespective of whether an exception is raised or not.
from("direct:start") .doTry() .process(new ProcessorFail()) .to("mock:result") .doCatch(IOException.class, IllegalStateException.class) .to("mock:catch") .doFinally() .to("mock:finally") .end();
<route> <from uri="direct:start"/> <!-- here the try starts. its a try .. catch .. finally just as regular java code --> <doTry> <process ref="processorFail"/> <to uri="mock:result"/> <doCatch> <!-- catch multiple exceptions --> <exception>java.io.IOException</exception> <exception>java.lang.IllegalStateException</exception> <to uri="mock:catch"/> </doCatch> <doFinally> <to uri="mock:finally"/> </doFinally> </doTry> </route>
Rethrowing exceptions in doCatch
doCatch()
clause by calling the handled()
sub-clause with its argument set to false
, as follows:
from("direct:start")
.doTry()
.process(new ProcessorFail())
.to("mock:result")
.doCatch(IOException.class)
// mark this as NOT handled, eg the caller will also get the exception
.handled(false)
.to("mock:io")
.doCatch(Exception.class)
// and catch all other exceptions
.to("mock:error")
.end();
IOException
is caught by doCatch()
, the current exchange is sent to the mock:io
endpoint, and then the IOException
is rethrown. This gives the consumer endpoint at the start of the route (in the from()
command) an opportunity to handle the exception as well.
<route> <from uri="direct:start"/> <doTry> <process ref="processorFail"/> <to uri="mock:result"/> <doCatch> <exception>java.io.IOException</exception> <!-- mark this as NOT handled, eg the caller will also get the exception --> <handled> <constant>false</constant> </handled> <to uri="mock:io"/> </doCatch> <doCatch> <!-- and catch all other exceptions they are handled by default (ie handled = true) --> <exception>java.lang.Exception</exception> <to uri="mock:error"/> </doCatch> </doTry> </route>
Conditional exception catching using onWhen
doCatch()
clause is that you can conditionalize the catching of exceptions based on an expression that is evaluated at run time. In other words, if you catch an exception using a clause of the form, doCatch(ExceptionList).doWhen(Expression)
, an exception will only be caught, if the predicate expression, Expression, evaluates to true
at run time.
doTry
block will catch the exceptions, IOException
and IllegalStateException
, only if the exception message contains the word, Severe
:
from("direct:start")
.doTry()
.process(new ProcessorFail())
.to("mock:result")
.doCatch(IOException.class, IllegalStateException.class)
.onWhen(exceptionMessage().contains("Severe"))
.to("mock:catch")
.doCatch(CamelExchangeException.class)
.to("mock:catchCamel")
.doFinally()
.to("mock:finally")
.end();
<route> <from uri="direct:start"/> <doTry> <process ref="processorFail"/> <to uri="mock:result"/> <doCatch> <exception>java.io.IOException</exception> <exception>java.lang.IllegalStateException</exception> <onWhen> <simple>${exception.message} contains 'Severe'</simple> </onWhen> <to uri="mock:catch"/> </doCatch> <doCatch> <exception>org.apache.camel.CamelExchangeException</exception> <to uri="mock:catchCamel"/> </doCatch> <doFinally> <to uri="mock:finally"/> </doFinally> </doTry> </route>
Nested Conditions in doTry
dotry()
creates a try or catch block for handling exceptions and is useful for route specific error handling.
ChoiceDefinition
, you can use the following doTry
blocks:
from("direct:wayne-get-token").setExchangePattern(ExchangePattern.InOut) .doTry() .to("https4://wayne-token-service") .choice() .when().simple("${header.CamelHttpResponseCode} == '200'") .convertBodyTo(String.class) .setHeader("wayne-token").groovy("body.replaceAll('\"','')") .log(">> Wayne Token : ${header.wayne-token}") .endChoice() doCatch(java.lang.Class (java.lang.Exception>) .log(">> Exception") .endDoTry(); from("direct:wayne-get-token").setExchangePattern(ExchangePattern.InOut) .doTry() .to("https4://wayne-token-service") .doCatch(Exception.class) .log(">> Exception") .endDoTry();
2.3.4. Propagating SOAP Exceptions
Overview
How to propagate stack trace information
dataFormat
to PAYLOAD
and set the faultStackTraceEnabled
property to true
in the cxfEndpoint
element, as follows:
<cxf:cxfEndpoint id="router" address="http://localhost:9002/TestMessage" wsdlURL="ship.wsdl" endpointName="s:TestSoapEndpoint" serviceName="s:TestService" xmlns:s="http://test"> <cxf:properties> <!-- enable sending the stack trace back to client; the default value is false--> <entry key="faultStackTraceEnabled" value="true" /> <entry key="dataFormat" value="PAYLOAD" /> </cxf:properties> </cxf:cxfEndpoint>
Caused by
). If you want to include the causing exception in the stack trace, set the exceptionMessageCauseEnabled
property to true
in the cxfEndpoint
element, as follows:
<cxf:cxfEndpoint id="router" address="http://localhost:9002/TestMessage"
wsdlURL="ship.wsdl"
endpointName="s:TestSoapEndpoint"
serviceName="s:TestService"
xmlns:s="http://test">
<cxf:properties>
<!-- enable to show the cause exception message and the default value is false -->
<entry key="exceptionMessageCauseEnabled" value="true" />
<!-- enable to send the stack trace back to client, the default value is false-->
<entry key="faultStackTraceEnabled" value="true" />
<entry key="dataFormat" value="PAYLOAD" />
</cxf:properties>
</cxf:cxfEndpoint>
exceptionMessageCauseEnabled
flag for testing and diagnostic purposes. It is normal practice for servers to conceal the original cause of an exception to make it harder for hostile users to probe the server.
2.4. Bean Integration
Overview
- Conventional method signatures — If the method signature conforms to certain conventions, the parameter binding can use Java reflection to determine what parameters to pass.
- Annotations and dependency injection — For a more flexible binding mechanism, employ Java annotations to specify what to inject into the method's arguments. This dependency injection mechanism relies on Spring 2.5 component scanning. Normally, if you are deploying your Apache Camel application into a Spring container, the dependency injection mechanism will work automatically.
- Explicitly specified parameters — You can specify parameters explicitly (either as constants or using the Simple language), at the point where the bean is invoked.
Bean registry
Registry plug-in strategy
Registry Implementation | Camel Component with Registry Plug-In |
---|---|
Spring bean registry | camel-spring |
Guice bean registry | camel-guice |
Blueprint bean registry | camel-blueprint |
OSGi service registry | deployed in OSGi container |
JNDI registry |
ApplicationContextRegistry
plug-in is automatically installed in the current CamelContext
instance.
CamelContext
automatically sets up a registry chain for resolving bean instances: the registry chain consists of the OSGi registry, followed by the Blueprint (or Spring) registry.
Accessing a bean created in Java
bean()
processor, which binds the inbound exchange to a method on the Java object. For example, to process inbound exchanges using the class, MyBeanProcessor
, define a route like the following:
from("file:data/inbound") .bean(MyBeanProcessor.class, "processBody") .to("file:data/outbound");
bean()
processor creates an instance of MyBeanProcessor
type and invokes the processBody()
method to process inbound exchanges. This approach is adequate if you only want to access the MyBeanProcessor
instance from a single route. However, if you want to access the same MyBeanProcessor
instance from multiple routes, use the variant of bean()
that takes the Object
type as its first argument. For example:
MyBeanProcessor myBean = new MyBeanProcessor(); from("file:data/inbound") .bean(myBean, "processBody") .to("file:data/outbound"); from("activemq:inboundData") .bean(myBean, "processBody") .to("activemq:outboundData");
Accessing overloaded bean methods
MyBeanBrocessor
class has two overloaded methods, processBody(String)
and processBody(String,String)
, you can invoke the latter overloaded method as follows:
from("file:data/inbound") .bean(MyBeanProcessor.class, "processBody(String,String)") .to("file:data/outbound");
*
. For example, to invoke a method named processBody
that takes two parameters, irrespective of the exact type of the parameters, invoke the bean()
processor as follows:
from("file:data/inbound") .bean(MyBeanProcessor.class, "processBody(*,*)") .to("file:data/outbound");
processBody(Exchange)
—or a fully qualified type name—for example, processBody(org.apache.camel.Exchange)
.
Specify parameters explicitly
- Boolean:
true
orfalse
. - Numeric:
123
,7
, and so on. - String:
'In single quotes'
or"In double quotes"
. - Null object:
null
.
from("file:data/inbound") .bean(MyBeanProcessor.class, "processBody(String, 'Sample string value', true, 7)") .to("file:data/outbound");
title
header to a bean method:
from("file:data/inbound") .bean(MyBeanProcessor.class, "processBodyAndHeader(${body},${header.title})") .to("file:data/outbound");
java.util.Map
:
from("file:data/inbound") .bean(MyBeanProcessor.class, "processBodyAndAllHeaders(${body},${header})") .to("file:data/outbound");
Basic method signatures
Method signature for processing message bodies
String
argument and returns a String
value. For example:
// Java package com.acme; public class MyBeanProcessor { public String processBody(String body) { // Do whatever you like to 'body'... return newBody; } }
Method signature for processing exchanges
org.apache.camel.Exchange
parameter and returns void
. For example:
// Java package com.acme; public class MyBeanProcessor { public void processExchange(Exchange exchange) { // Do whatever you like to 'exchange'... exchange.getIn().setBody("Here is a new message body!"); } }
Accessing a Spring bean from Spring XML
bean
element. The following example shows how to create an instance of MyBeanProcessor
:
<beans ...> ... <bean id="myBeanId" class="com.acme.MyBeanProcessor"/> </beans>
bean
element, see The IoC Container from the Spring reference guide.
beanRef()
processor invokes the MyBeanProcessor.processBody()
method on the specified bean instance. You can also invoke the bean from within a Spring XML route, using the Camel schema's bean
element. For example:
<camelContext id="CamelContextID" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="file:data/inbound"/> <bean ref="myBeanId" method="processBody"/> <to uri="file:data/outbound"/> </route> </camelContext>
cache
option to true
, which avoids looking up the registry every time a bean is used. For example, to enable caching, you can set the cache
attribute on the bean
element as follows:
<bean ref="myBeanId" method="processBody" cache="true"/>
Accessing a Spring bean from Java
bean
element, you can reference it from Java using the bean's ID (the value of the bean
element's id
attribute). For example, given the bean
element with ID equal to myBeanId
, you can reference the bean in a Java DSL route using the beanRef()
processor, as follows:
from("file:data/inbound").beanRef("myBeanId", "processBody").to("file:data/outbound");
@BeanInject
annotation as follows:
// Java import org.apache.camel.@BeanInject; ... public class MyRouteBuilder extends RouteBuilder { @BeanInject("myBeanId") com.acme.MyBeanProcessor bean; public void configure() throws Exception { .. } }
@BeanInject
annotation, Camel looks up the registry by type, but this only works if there is just a single bean of the given type. For example, to look up and inject the bean of com.acme.MyBeanProcessor
type:
@BeanInject com.acme.MyBeanProcessor bean;
Bean shutdown order in Spring XML
- Shut down the
camelContext
instance, followed by; - Shut down the used beans.
camelContext
appear in the Spring XML file. In order to avoid random errors due to incorrect shutdown order, therefore, the camelContext
is configured to shut down before any of the other beans in the Spring XML file. This is the default behaviour since Apache Camel 2.13.0.
shutdownEager
attribute on the camelContext
element to false
. In this case, you could potentially exercise more fine-grained control over shutdown order using the Spring depends-on
attribute.
Parameter binding annotations
Basic annotations
org.apache.camel
Java package that you can use to inject message data into the arguments of a bean method.
Annotation | Meaning | Parameter? |
---|---|---|
@Attachments | Binds to a list of attachments. | |
@Body | Binds to an inbound message body. | |
@Header | Binds to an inbound message header. | String name of the header. |
@Headers | Binds to a java.util.Map of the inbound message headers. | |
@OutHeaders | Binds to a java.util.Map of the outbound message headers. | |
@Property | Binds to a named exchange property. | String name of the property. |
@Properties | Binds to a java.util.Map of the exchange properties. |
processExchange()
method arguments.
// Java import org.apache.camel.*; public class MyBeanProcessor { public void processExchange( @Header(name="user") String user, @Body String body, Exchange exchange ) { // Do whatever you like to 'exchange'... exchange.getIn().setBody(body + "UserName = " + user); } }
org.apache.camel.Exchange
argument.
Expression language annotations
org.apache.camel.language
package (and sub-packages, for the non-core annotations) that you can use to inject message data into the arguments of a bean method.
Annotation | Description |
---|---|
@Bean | Injects a Bean expression. |
@Constant | Injects a Constant expression |
@EL | Injects an EL expression. |
@Groovy | Injects a Groovy expression. |
@Header | Injects a Header expression. |
@JavaScript | Injects a JavaScript expression. |
@OGNL | Injects an OGNL expression. |
@PHP | Injects a PHP expression. |
@Python | Injects a Python expression. |
@Ruby | Injects a Ruby expression. |
@Simple | Injects a Simple expression. |
@XPath | Injects an XPath expression. |
@XQuery | Injects an XQuery expression. |
@XPath
annotation to extract a username and a password from the body of an incoming message in XML format:
// Java import org.apache.camel.language.*; public class MyBeanProcessor { public void checkCredentials( @XPath("/credentials/username/text()") String user, @XPath("/credentials/password/text()") String pass ) { // Check the user/pass credentials... ... } }
@Bean
annotation is a special case, because it enables you to inject the result of invoking a registered bean. For example, to inject a correlation ID into a method argument, you can use the @Bean
annotation to invoke an ID generator class, as follows:
// Java import org.apache.camel.language.*; public class MyBeanProcessor { public void processCorrelatedMsg( @Bean("myCorrIdGenerator") String corrId, @Body String body ) { // Check the user/pass credentials... ... } }
myCorrIdGenerator
, is the bean ID of the ID generator instance. The ID generator class can be instantiated using the spring bean
element, as follows:
<beans ...> ... <bean id="myCorrIdGenerator" class="com.acme.MyIdGenerator"/> </beans>
MySimpleIdGenerator
class could be defined as follows:
// Java package com.acme; public class MyIdGenerator { private UserManager userManager; public String generate( @Header(name = "user") String user, @Body String payload ) throws Exception { User user = userManager.lookupUser(user); String userId = user.getPrimaryId(); String id = userId + generateHashCodeForPayload(payload); return id; } }
MyIdGenerator
. The only restriction on the generate()
method signature is that it must return the correct type to inject into the argument annotated by @Bean
. Because the @Bean
annotation does not let you specify a method name, the injection mechanism simply invokes the first method in the referenced bean that has the matching return type.
@Bean
, @Constant
, @Simple
, and @XPath
). For non-core components, however, you will have to make sure that you load the relevant component. For example, to use the OGNL script, you must load the camel-ognl
component.
Inherited annotations
Header
annotation and a Body
annotation, as follows:
// Java import org.apache.camel.*; public interface MyBeanProcessorIntf { void processExchange( @Header(name="user") String user, @Body String body, Exchange exchange ); }
MyBeanProcessor
, now inherit the annotations defined in the base interface, as follows:
// Java import org.apache.camel.*; public class MyBeanProcessor implements MyBeanProcessorIntf { public void processExchange( String user, // Inherits Header annotation String body, // Inherits Body annotation Exchange exchange ) { ... } }
Interface implementations
protected
, private
or in package-only
scope. If you try to invoke a method on an implementation class that is restricted in this way, the bean binding falls back to invoking the corresponding interface method, which is publicly accessible.
BeanIntf
interface:
// Java public interface BeanIntf { void processBodyAndHeader(String body, String title); }
BeanIntf
interface is implemented by the following protected BeanIntfImpl
class:
// Java protected class BeanIntfImpl implements BeanIntf { void processBodyAndHeader(String body, String title) { ... } }
BeanIntf.processBodyAndHeader
method:
from("file:data/inbound") .bean(BeanIntfImpl.class, "processBodyAndHeader(${body}, ${header.title})") .to("file:data/outbound");
Invoking static methods
changeSomething()
:
// Java ... public final class MyStaticClass { private MyStaticClass() { } public static String changeSomething(String s) { if ("Hello World".equals(s)) { return "Bye World"; } return null; } public void doSomething() { // noop } }
changeSomething
method, as follows:
from("direct:a")
.bean(MyStaticClass.class, "changeSomething")
.to("mock:a");
MyStaticClass
.
Invoking an OSGi service
org.fusesource.example.HelloWorldOsgiService
, you could invoke the sayHello
method using the following bean integration code:
from("file:data/inbound") .bean(org.fusesource.example.HelloWorldOsgiService.class, "sayHello") .to("file:data/outbound");
<to uri="bean:org.fusesource.example.HelloWorldOsgiService?method=sayHello"/>
2.5. Creating Exchange Instances
Overview
Exchange
object, the easiest approach is to invoke the methods of the ExchangeBuilder
class, as described here.
ExchangeBuilder class
ExchangeBuilder
class is as follows:
org.apache.camel.builder.ExchangeBuilder
ExchangeBuilder
exposes the static method, anExchange
, which you can use to start building an exchange object.
Example
Hello World!
, and with headers containing username and password credentials:
// Java import org.apache.camel.Exchange; import org.apache.camel.builder.ExchangeBuilder; ... Exchange exch = ExchangeBuilder.anExchange(camelCtx) .withBody("Hello World!") .withHeader("username", "jdoe") .withHeader("password", "pass") .build();
ExchangeBuilder methods
ExchangeBuilder
class supports the following methods:
ExchangeBuilder anExchange(CamelContext context)
- (static method) Initiate building an exchange object.
Exchange build()
- Build the exchange.
ExchangeBuilder withBody(Object body)
- Set the message body on the exchange (that is, sets the exchange's In message body).
ExchangeBuilder withHeader(String key, Object value)
- Set a header on the exchange (that is, sets a header on the exchange's In message).
ExchangeBuilder withPattern(ExchangePattern pattern)
- Sets the exchange pattern on the exchange.
ExchangeBuilder withProperty(String key, Object value)
- Sets a property on the exchange.
2.6. Transforming Message Content
Abstract
2.6.1. Simple Message Transformations
Overview
World!
, to the end of the incoming message body.
Example 2.1. Simple Transformation of Incoming Messages
from("SourceURL").setBody(body().append(" World!")).to("TargetURL");
setBody()
command replaces the content of the incoming message's body.
API for simple transformations
org.apache.camel.model.ProcessorDefinition
org.apache.camel.builder.Builder
org.apache.camel.builder.ValueBuilder
ProcessorDefinition class
org.apache.camel.model.ProcessorDefinition
class defines the DSL commands you can insert directly into a router rule—for example, the setBody()
command in Example 2.1, “Simple Transformation of Incoming Messages”. Table 2.5, “Transformation Methods from the ProcessorDefinition Class” shows the ProcessorDefinition
methods that are relevant to transforming message content:
Method | Description |
---|---|
Type convertBodyTo(Class type) | Converts the IN message body to the specified type. |
Type removeFaultHeader(String name) | Adds a processor which removes the header on the FAULT message. |
Type removeHeader(String name) | Adds a processor which removes the header on the IN message. |
Type removeProperty(String name) | Adds a processor which removes the exchange property. |
ExpressionClause<ProcessorDefinition<Type>> setBody() | Adds a processor which sets the body on the IN message. |
Type setFaultBody(Expression expression) | Adds a processor which sets the body on the FAULT message. |
Type setFaultHeader(String name, Expression expression) | Adds a processor which sets the header on the FAULT message. |
ExpressionClause<ProcessorDefinition<Type>> setHeader(String name) | Adds a processor which sets the header on the IN message. |
Type setHeader(String name, Expression expression) | Adds a processor which sets the header on the IN message. |
ExpressionClause<ProcessorDefinition<Type>> setOutHeader(String name) | Adds a processor which sets the header on the OUT message. |
Type setOutHeader(String name, Expression expression) | Adds a processor which sets the header on the OUT message. |
ExpressionClause<ProcessorDefinition<Type>> setProperty(String name) | Adds a processor which sets the exchange property. |
Type setProperty(String name, Expression expression) | Adds a processor which sets the exchange property. |
ExpressionClause<ProcessorDefinition<Type>> transform() | Adds a processor which sets the body on the OUT message. |
Type transform(Expression expression) | Adds a processor which sets the body on the OUT message. |
Builder class
org.apache.camel.builder.Builder
class provides access to message content in contexts where expressions or predicates are expected. In other words, Builder
methods are typically invoked in the arguments of DSL commands—for example, the body()
command in Example 2.1, “Simple Transformation of Incoming Messages”. Table 2.6, “Methods from the Builder Class” summarizes the static methods available in the Builder
class.
Method | Description |
---|---|
static <E extends Exchange> ValueBuilder<E> body() | Returns a predicate and value builder for the inbound body on an exchange. |
static <E extends Exchange,T> ValueBuilder<E> bodyAs(Class<T> type) | Returns a predicate and value builder for the inbound message body as a specific type. |
static <E extends Exchange> ValueBuilder<E> constant(Object value) | Returns a constant expression. |
static <E extends Exchange> ValueBuilder<E> faultBody() | Returns a predicate and value builder for the fault body on an exchange. |
static <E extends Exchange,T> ValueBuilder<E> faultBodyAs(Class<T> type) | Returns a predicate and value builder for the fault message body as a specific type. |
static <E extends Exchange> ValueBuilder<E> header(String name) | Returns a predicate and value builder for headers on an exchange. |
static <E extends Exchange> ValueBuilder<E> outBody() | Returns a predicate and value builder for the outbound body on an exchange. |
static <E extends Exchange> ValueBuilder<E> outBodyAs(Class<T> type) | Returns a predicate and value builder for the outbound message body as a specific type. |
static ValueBuilder property(String name) | Returns a predicate and value builder for properties on an exchange. |
static ValueBuilder regexReplaceAll(Expression content, String regex, Expression replacement) | Returns an expression that replaces all occurrences of the regular expression with the given replacement. |
static ValueBuilder regexReplaceAll(Expression content, String regex, String replacement) | Returns an expression that replaces all occurrences of the regular expression with the given replacement. |
static ValueBuilder sendTo(String uri) | Returns an expression processing the exchange to the given endpoint uri. |
static <E extends Exchange> ValueBuilder<E> systemProperty(String name) | Returns an expression for the given system property. |
static <E extends Exchange> ValueBuilder<E> systemProperty(String name, String defaultValue) | Returns an expression for the given system property. |
ValueBuilder class
org.apache.camel.builder.ValueBuilder
class enables you to modify values returned by the Builder
methods. In other words, the methods in ValueBuilder
provide a simple way of modifying message content. Table 2.7, “Modifier Methods from the ValueBuilder Class” summarizes the methods available in the ValueBuilder
class. That is, the table shows only the methods that are used to modify the value they are invoked on (for full details, see the API Reference documentation).
Method | Description |
---|---|
ValueBuilder<E> append(Object value) | Appends the string evaluation of this expression with the given value. |
Predicate contains(Object value) | Create a predicate that the left hand expression contains the value of the right hand expression. |
ValueBuilder<E> convertTo(Class type) | Converts the current value to the given type using the registered type converters. |
ValueBuilder<E> convertToString() | Converts the current value a String using the registered type converters. |
Predicate endsWith(Object value) | |
<T> T evaluate(Exchange exchange, Class<T> type) | |
Predicate in(Object... values) | |
Predicate in(Predicate... predicates) | |
Predicate isEqualTo(Object value) | Returns true, if the current value is equal to the given value argument. |
Predicate isGreaterThan(Object value) | Returns true, if the current value is greater than the given value argument. |
Predicate isGreaterThanOrEqualTo(Object value) | Returns true, if the current value is greater than or equal to the given value argument. |
Predicate isInstanceOf(Class type) | Returns true, if the current value is an instance of the given type. |
Predicate isLessThan(Object value) | Returns true, if the current value is less than the given value argument. |
Predicate isLessThanOrEqualTo(Object value) | Returns true, if the current value is less than or equal to the given value argument. |
Predicate isNotEqualTo(Object value) | Returns true, if the current value is not equal to the given value argument. |
Predicate isNotNull() | Returns true, if the current value is not null . |
Predicate isNull() | Returns true, if the current value is null . |
Predicate matches(Expression expression) | |
Predicate not(Predicate predicate) | Negates the predicate argument. |
ValueBuilder prepend(Object value) | Prepends the string evaluation of this expression to the given value. |
Predicate regex(String regex) | |
ValueBuilder<E> regexReplaceAll(String regex, Expression<E> replacement) | Replaces all occurrencies of the regular expression with the given replacement. |
ValueBuilder<E> regexReplaceAll(String regex, String replacement) | Replaces all occurrencies of the regular expression with the given replacement. |
ValueBuilder<E> regexTokenize(String regex) | Tokenizes the string conversion of this expression using the given regular expression. |
ValueBuilder sort(Comparator comparator) | Sorts the current value using the given comparator. |
Predicate startsWith(Object value) | Returns true, if the current value matches the string value of the value argument. |
ValueBuilder<E> tokenize() | Tokenizes the string conversion of this expression using the comma token separator. |
ValueBuilder<E> tokenize(String token) | Tokenizes the string conversion of this expression using the given token separator. |
2.6.2. Marshalling and Unmarshalling
Java DSL commands
marshal()
— Converts a high-level data format to a low-level data format.unmarshal
() — Converts a low-level data format to a high-level data format.
Data formats
- Java serialization
- JAXB
- XMLBeans
- XStream
Java serialization
from("SourceURL").unmarshal().serialization() .<FurtherProcessing>.to("TargetURL");
<camelContext id="serialization" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURL"/> <unmarshal> <serialization/> </unmarshal> <to uri="TargetURL"/> </route> </camelContext>
JAXB
org.apache.camel.spi.DataFormat jaxb = new org.apache.camel.model.dataformat.JaxbDataFormat("GeneratedPackageName"); from("SourceURL").unmarshal(jaxb) .<FurtherProcessing>.to("TargetURL");
<camelContext id="jaxb" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURL"/> <unmarshal> <jaxb prettyPrint="true" contextPath="GeneratedPackageName"/> </unmarshal> <to uri="TargetURL"/> </route> </camelContext>
XMLBeans
from("SourceURL").unmarshal().xmlBeans() .<FurtherProcessing>.to("TargetURL");
<camelContext id="xmlBeans" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURL"/> <unmarshal> <xmlBeans prettyPrint="true"/> </unmarshal> <to uri="TargetURL"/> </route> </camelContext>
XStream
from("SourceURL").unmarshal().xstream() .<FurtherProcessing>.to("TargetURL");
2.6.3. Endpoint Bindings
What is a binding?
DataFormatBinding
DataFormatBinding
class is useful for the specific case where you want to define a binding that marshals and unmarshals a particular data format (see Section 2.6.2, “Marshalling and Unmarshalling”). In this case, all that you need to do to create a binding is to create a DataFormatBinding
instance, passing a reference to the relevant data format in the constructor.
jaxb
) that is capable of marshalling and unmarshalling the JAXB data format when it is associated with an Apache Camel endpoint:
Example 2.2. JAXB Binding
<beans ... >
...
<bean id="jaxb" class="org.apache.camel.processor.binding.DataFormatBinding">
<constructor-arg ref="jaxbformat"/>
</bean>
<bean id="jaxbformat" class="org.apache.camel.model.dataformat.JaxbDataFormat">
<property name="prettyPrint" value="true"/>
<property name="contextPath" value="org.apache.camel.example"/>
</bean>
</beans>
Associating a binding with an endpoint
Binding URI
binding:NameOfBinding
, where NameOfBinding
is the bean ID of the binding (for example, the ID of a binding bean created in Spring XML).
<beans ...> ... <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="binding:jaxb:activemq:orderQueue"/> <to uri="binding:jaxb:activemq:otherQueue"/> </route> </camelContext> ... </beans>
BindingComponent
BindingComponent
class.
jaxb
binding with activemq
endpoints, you could define a new BindingComponent
instance as follows:
<beans ... >
...
<bean id="jaxbmq" class="org.apache.camel.component.binding.BindingComponent">
<constructor-arg ref="jaxb"/>
<constructor-arg value="activemq:foo."/>
</bean>
<bean id="jaxb" class="org.apache.camel.processor.binding.DataFormatBinding">
<constructor-arg ref="jaxbformat"/>
</bean>
<bean id="jaxbformat" class="org.apache.camel.model.dataformat.JaxbDataFormat">
<property name="prettyPrint" value="true"/>
<property name="contextPath" value="org.apache.camel.example"/>
</bean>
</beans>
jaxbmq
defines a URI prefix. You can now use the jaxbmq
ID as the scheme for an endpoint URI. For example, you can define the following route using this binding component:
<beans ...> ... <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="jaxbmq:firstQueue"/> <to uri="jaxbmq:otherQueue"/> </route> </camelContext> ... </beans>
<beans ...> ... <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="binding:jaxb:activemq:foo.firstQueue"/> <to uri="binding:jaxb:activemq:foo.otherQueue"/> </route> </camelContext> ... </beans>
org.apache.camel.spi.HasBinding
interface.
BindingComponent constructors
BindingComponent
class supports the following constructors:
public BindingComponent()
- No arguments form. Use property injection to configure the binding component instance.
public BindingComponent(Binding binding)
- Associate this binding component with the specified
Binding
object,binding
. public BindingComponent(Binding binding, String uriPrefix)
- Associate this binding component with the specified
Binding
object,binding
, and URI prefix,uriPrefix
. This is the most commonly used constructor. public BindingComponent(Binding binding, String uriPrefix, String uriPostfix)
- This constructor supports the additional URI post-fix,
uriPostfix
, argument, which is automatically appended to any URIs defined using this binding component.
Implementing a custom binding
DataFormatBinding
, which is used for marshalling and unmarshalling data formats, you can implement your own custom bindings. Define a custom binding as follows:
- Implement an
org.apache.camel.Processor
class to perform a transformation on messages incoming to a consumer endpoint (appearing in afrom
element). - Implement a complementary
org.apache.camel.Processor
class to perform the reverse transformation on messages outgoing from a producer endpoint (appearing in ato
element). - Implement the
org.apache.camel.spi.Binding
interface, which acts as a factory for the processor instances.
Binding interface
org.apache.camel.spi.Binding
interface, which you must implement to define a custom binding.
Example 2.3. The org.apache.camel.spi.Binding Interface
// Java package org.apache.camel.spi; import org.apache.camel.Processor; /** * Represents a <a href="http://camel.apache.org/binding.html">Binding</a> or contract * which can be applied to an Endpoint; such as ensuring that a particular * <a href="http://camel.apache.org/data-format.html">Data Format</a> is used on messages in and out of an endpoint. */ public interface Binding { /** * Returns a new {@link Processor} which is used by a producer on an endpoint to implement * the producer side binding before the message is sent to the underlying endpoint. */ Processor createProduceProcessor(); /** * Returns a new {@link Processor} which is used by a consumer on an endpoint to process the * message with the binding before its passed to the endpoint consumer producer. */ Processor createConsumeProcessor(); }
When to use bindings
2.7. Property Placeholders
Overview
{{remote.host}}
and {{remote.port}}
:
from("direct:start").to("http://{{remote.host}}:{{remote.port}}");
# Java properties file remote.host=myserver.com remote.port=8080
Property files
Key=Value
. Lines with #
or !
as the first non-blank character are treated as comments.
Example 2.4. Sample Property File
# Property placeholder settings # (in Java properties file format) cool.end=mock:result cool.result=result cool.concat=mock:{{cool.result}} cool.start=direct:cool cool.showid=true cheese.end=mock:cheese cheese.quote=Camel rocks cheese.type=Gouda bean.foo=foo bean.bar=bar
Resolving properties
-
classpath:PathName,PathName,...
- (Default) Specifies locations on the classpath, where PathName is a file pathname delimited using forward slashes.
-
file:PathName,PathName,...
- Specifies locations on the file system, where PathName is a file pathname delimited using forward slashes.
-
ref:BeanID
- Specifies the ID of a
java.util.Properties
object in the registry. -
blueprint:BeanID
- Specifies the ID of a
cm:property-placeholder
bean, which is used in the context of an OSGi blueprint file to access properties defined in the OSGi Configuration Admin service. For details, see the section called “Integration with OSGi blueprint property placeholders”.
com/fusesource/cheese.properties
property file and the com/fusesource/bar.properties
property file, both located on the classpath, you would use the following location string:
com/fusesource/cheese.properties,com/fusesource/bar.properties
classpath:
prefix in this example, because the classpath resolver is used by default.
Specifying locations using system properties and environment variables
${PropertyName}
. For example, if the root directory of Red Hat JBoss Fuse is stored in the Java system property, karaf.home
, you could embed that directory value in a file location, as follows:
file:${karaf.home}/etc/foo.properties
${env:VarName}
. For example, if the root directory of JBoss Fuse is stored in the environment variable, SMX_HOME
, you could embed that directory value in a file location, as follows:
file:${env:SMX_HOME}/etc/foo.properties
Configuring the properties component
// Java import org.apache.camel.component.properties.PropertiesComponent; ... PropertiesComponent pc = new PropertiesComponent(); pc.setLocation("com/fusesource/cheese.properties,com/fusesource/bar.properties"); context.addComponent("properties", pc);
addComponent()
call, the name of the properties component must be set to properties
.
propertyPlacholder
element, as follows:
<camelContext ...> <propertyPlaceholder id="properties" location="com/fusesource/cheese.properties,com/fusesource/bar.properties" /> </camelContext>
.properties
files when it is being initialized, you can set the ignoreMissingLocation
option to true
(normally, a missing .properties
file would result in an error being raised).
ignoreMissingLocation
option to true
.
Placeholder syntax
- In endpoint URIs and in Spring XML files—the placeholder is specified as
{{Key}}
. - When setting XML DSL attributes—
xs:string
attributes are set using the following syntax:AttributeName="{{Key}}"
Other attribute types (for example,xs:int
orxs:boolean
) must be set using the following syntax:prop:AttributeName="Key"
Whereprop
is associated with thehttp://camel.apache.org/schema/placeholder
namespace. - When setting Java DSL EIP options—to set an option on an Enterprise Integration Pattern (EIP) command in the Java DSL, add a
placeholder()
clause like the following to the fluent DSL:.placeholder("OptionName", "Key")
- In Simple language expressions—the placeholder is specified as
${properties:Key}
.
Substitution in endpoint URIs
{{Key}}
. For example, given the property settings shown in Example 2.4, “Sample Property File”, you could define a route as follows:
from("{{cool.start}}") .to("log:{{cool.start}}?showBodyType=false&showExchangeId={{cool.showid}}") .to("mock:{{cool.result}}");
properties
bean ID in the registry to find the property component. If you prefer, you can explicitly specify the scheme in the endpoint URIs. For example, by prefixing properties:
to each of the endpoint URIs, you can define the following equivalent route:
from("properties:{{cool.start}}") .to("properties:log:{{cool.start}}?showBodyType=false&showExchangeId={{cool.showid}}") .to("properties:mock:{{cool.result}}");
location
option as follows:
from("direct:start").to("properties:{{bar.end}}?location=com/mycompany/bar.properties");
Substitution in Spring XML files
{{Key}}
. For example, you could define a jmxAgent
element using property placeholders, as follows:
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <propertyPlaceholder id="properties" location="org/apache/camel/spring/jmx.properties"/> <!-- we can use property placeholders when we define the JMX agent --> <jmxAgent id="agent" registryPort="{{myjmx.port}}" usePlatformMBeanServer="{{myjmx.usePlatform}}" createConnector="true" statisticsLevel="RoutesOnly" /> <route> <from uri="seda:start"/> <to uri="mock:result"/> </route> </camelContext>
Substitution of XML DSL attribute values
xs:string
type—for example, <jmxAgent registryPort="{{myjmx.port}}" ...>
. But for attributes of any other type (for example, xs:int
or xs:boolean
), you must use the special syntax, prop:AttributeName="Key"
.
stop.flag
property to have the value, true
, you can use this property to set the stopOnException
boolean attribute, as follows:
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:prop="http://camel.apache.org/schema/placeholder" ... > <bean id="illegal" class="java.lang.IllegalArgumentException"> <constructor-arg index="0" value="Good grief!"/> </bean> <camelContext xmlns="http://camel.apache.org/schema/spring"> <propertyPlaceholder id="properties" location="classpath:org/apache/camel/component/properties/myprop.properties" xmlns="http://camel.apache.org/schema/spring"/> <route> <from uri="direct:start"/> <multicast prop:stopOnException="stop.flag"> <to uri="mock:a"/> <throwException ref="damn"/> <to uri="mock:b"/> </multicast> </route> </camelContext> </beans>
prop
prefix must be explicitly assigned to the http://camel.apache.org/schema/placeholder
namespace in your Spring file, as shown in the beans
element of the preceding example.
Substitution of Java DSL EIP options
placeholder("OptionName", "Key")
.
stop.flag
property to have the value, true
, you can use this property to set the stopOnException
option of the multicast EIP, as follows:
from("direct:start") .multicast().placeholder("stopOnException", "stop.flag") .to("mock:a").throwException(new IllegalAccessException("Damn")).to("mock:b");
Substitution in Simple language expressions
${properties:Key}
. For example, you can substitute the cheese.quote
placeholder inside a Simple expression, as follows:
from("direct:start") .transform().simple("Hi ${body} do you think ${properties:cheese.quote}?");
${properties:Key:DefaultVal}
. For example:
from("direct:start") .transform().simple("Hi ${body} do you think ${properties:cheese.quote:cheese is good}?");
${properties-location:Location:Key}
. For example, to substitute the bar.quote
placeholder using the settings from the com/mycompany/bar.properties
property file, you can define a Simple expression as follows:
from("direct:start") .transform().simple("Hi ${body}. ${properties-location:com/mycompany/bar.properties:bar.quote}.");
Using Property Placeholders in the XML DSL
xs:string
type attributes were used to support placeholders in the XML DSL. For example, the timeout attribute would be a xs:int
type. Therefore, you cannot set a string value as the placeholder key.
stopOnException
as the value of the placeholder with the key stop
. Also, in the properties file, define the value as
stop=true
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:prop="http://camel.apache.org/schema/placeholder" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd "> <!-- Notice in the declaration above, we have defined the prop prefix as the Camel placeholder namespace --> <bean id="damn" class="java.lang.IllegalArgumentException"> <constructor-arg index="0" value="Damn"/> </bean> <camelContext xmlns="http://camel.apache.org/schema/spring"> <propertyPlaceholder id="properties" location="classpath:org/apache/camel/component/properties/myprop.properties" xmlns="http://camel.apache.org/schema/spring"/> <route> <from uri="direct:start"/> <!-- use prop namespace, to define a property placeholder, which maps to option stopOnException={{stop}} --> <multicast prop:stopOnException="stop"> <to uri="mock:a"/> <throwException ref="damn"/> <to uri="mock:b"/> </multicast> </route> </camelContext> </beans>
Integration with OSGi blueprint property placeholders
Implicit blueprint integration
camelContext
element inside an OSGi blueprint file, the Apache Camel property placeholder mechanism automatically integrates with the blueprint property placeholder mechanism. That is, placeholders obeying the Apache Camel syntax (for example, {{cool.end}}
) that appear within the scope of camelContext
are implicitly resolved by looking up the blueprint property placeholder mechanism.
{{result}}
:
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:cm="http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.0.0" xsi:schemaLocation=" http://www.osgi.org/xmlns/blueprint/v1.0.0 http://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd"> <!-- OSGI blueprint property placeholder --> <cm:property-placeholder id="myblueprint.placeholder" persistent-id="camel.blueprint"> <!-- list some properties for this test --> <cm:default-properties> <cm:property name="result" value="mock:result"/> </cm:default-properties> </cm:property-placeholder> <camelContext xmlns="http://camel.apache.org/schema/blueprint"> <!-- in the route we can use {{ }} placeholders which will look up in blueprint, as Camel will auto detect the OSGi blueprint property placeholder and use it --> <route> <from uri="direct:start"/> <to uri="mock:foo"/> <to uri="{{result}}"/> </route> </camelContext> </blueprint>
cm:property-placeholder
bean. In the preceding example, the cm:property-placeholder
bean is associated with the camel.blueprint
persistent ID, where a persistent ID is the standard way of referencing a group of related properties from the OSGi Configuration Admin service. In other words, the cm:property-placeholder
bean provides access to all of the properties defined under the camel.blueprint
persistent ID. It is also possible to specify default values for some of the properties (using the nested cm:property
elements).
cm:property-placeholder
in the bean registry. If it finds such an instance, it automatically integrates the Apache Camel placeholder mechanism, so that placeholders like, {{result}}
, are resolved by looking up the key in the blueprint property placeholder mechanism (in this example, through the myblueprint.placeholder
bean).
${Key}
. Hence, outside the scope of a camelContext
element, the placeholder syntax you must use is ${Key}
. Whereas, inside the scope of a camelContext
element, the placeholder syntax you must use is {{Key}}
.
Explicit blueprint integration
propertyPlaceholder
element and specify the resolver locations explicitly.
propertyPlaceholder
instance:
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:cm="http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.0.0" xsi:schemaLocation=" http://www.osgi.org/xmlns/blueprint/v1.0.0 http://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd"> <!-- OSGI blueprint property placeholder --> <cm:property-placeholder id="myblueprint.placeholder" persistent-id="camel.blueprint"> <!-- list some properties for this test --> <cm:default-properties> <cm:property name="result" value="mock:result"/> </cm:default-properties> </cm:property-placeholder> <camelContext xmlns="http://camel.apache.org/schema/blueprint"> <!-- using Camel properties component and refer to the blueprint property placeholder by its id --> <propertyPlaceholder id="properties" location="blueprint:myblueprint.placeholder"/> <!-- in the route we can use {{ }} placeholders which will lookup in blueprint --> <route> <from uri="direct:start"/> <to uri="mock:foo"/> <to uri="{{result}}"/> </route> </camelContext> </blueprint>
propertyPlaceholder
element specifies explicitly which cm:property-placeholder
bean to use by setting the location to blueprint:myblueprint.placeholder
. That is, the blueprint:
resolver explicitly references the ID, myblueprint.placeholder
, of the cm:property-placeholder
bean.
cm:property-placeholder
bean defined in the blueprint file and you need to specify which one to use. It also makes it possible to source properties from multiple locations, by specifying a comma-separated list of locations. For example, if you wanted to look up properties both from the cm:property-placeholder
bean and from the properties file, myproperties.properties
, on the classpath, you could define the propertyPlaceholder
element as follows:
<propertyPlaceholder id="properties" location="blueprint:myblueprint.placeholder,classpath:myproperties.properties"/>
Integration with Spring property placeholders
org.apache.camel.spring.spi.BridgePropertyPlaceholderConfigurer
.
BridgePropertyPlaceholderConfigurer
, which replaces both Apache Camel's propertyPlaceholder
element and Spring's ctx:property-placeholder
element in the Spring XML file. You can then refer to the configured properties using either the Spring ${PropName}
syntax or the Apache Camel {{PropName}}
syntax.
cheese.properties
file:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:osgix="http://www.springframework.org/schema/osgi-compendium" xmlns:ctx="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/osgi http://www.springframework.org/schema/osgi/spring-osgi.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/osgi-compendium http://www.springframework.org/schema/osgi-compendium/spring-osgi-compendium.xsd "> <!-- Bridge Spring property placeholder with Camel --> <!-- Do not use <ctx:property-placeholder ... > at the same time --> <bean id="bridgePropertyPlaceholder" class="org.apache.camel.spring.spi.BridgePropertyPlaceholderConfigurer"> <property name="location" value="classpath:org/apache/camel/component/properties/cheese.properties"/> </bean> <!-- A bean that uses Spring property placeholder --> <!-- The ${hi} is a spring property placeholder --> <bean id="hello" class="org.apache.camel.component.properties.HelloBean"> <property name="greeting" value="${hi}"/> </bean> <camelContext xmlns="http://camel.apache.org/schema/spring"> <!-- Use Camel's property placeholder {{ }} style --> <route> <from uri="direct:{{cool.bar}}"/> <bean ref="hello"/> <to uri="{{cool.end}}"/> </route> </camelContext> </beans>
location
attribute of the BridgePropertyPlaceholderConfigurer
to point at a Spring properties file. The Spring properties file syntax is fully supported.
2.8. Threading Model
Java thread pool API
ExecutorService
interface, which represents a thread pool. Using the concurrency API, you can create many different kinds of thread pool, covering a wide range of scenarios.
Apache Camel thread pool API
org.apache.camel.spi.ExecutorServiceManager
type) for all of the thread pools in your Apache Camel application. Centralising the creation of thread pools in this way provides several advantages, including:
- Simplified creation of thread pools, using utility classes.
- Integrating thread pools with graceful shutdown.
- Threads automatically given informative names, which is beneficial for logging and management.
Component threading model
ExecutorServiceManager
object.
Processor threading model
Processor | Java DSL | XML DSL |
---|---|---|
aggregate |
parallelProcessing() executorService() executorServiceRef() |
@parallelProcessing @executorServiceRef |
multicast |
parallelProcessing() executorService() executorServiceRef() |
@parallelProcessing @executorServiceRef |
recipientList |
parallelProcessing() executorService() executorServiceRef() |
@parallelProcessing @executorServiceRef |
split |
parallelProcessing() executorService() executorServiceRef() |
@parallelProcessing @executorServiceRef |
threads |
executorService() executorServiceRef() poolSize() maxPoolSize() keepAliveTime() timeUnit() maxQueueSize() rejectedPolicy() |
@executorServiceRef @poolSize @maxPoolSize @keepAliveTime @timeUnit @maxQueueSize @rejectedPolicy |
wireTap |
wireTap(String uri, ExecutorService executorService) wireTap(String uri, String executorServiceRef) |
@executorServiceRef |
threads DSL options
threads
processor is a general-purpose DSL command, which you can use to introduce a thread pool into a route. It supports the following options to customize the thread pool:
poolSize()
- Minimum number of threads in the pool (and initial pool size).
maxPoolSize()
- Maximum number of threads in the pool.
keepAliveTime()
- If any threads are idle for longer than this period of time (specified in seconds), they are terminated.
timeUnit()
- Time unit for keep alive, specified using the
java.util.concurrent.TimeUnit
type. maxQueueSize()
- Maximum number of pending tasks that this thread pool can store in its incoming task queue.
rejectedPolicy()
- Specifies what course of action to take, if the incoming task queue is full. See Table 2.10, “Thread Pool Builder Options”
executorServiceRef
option (for example, you cannot use these options to override the settings in the thread pool referenced by an executorServiceRef
option). Apache Camel validates the DSL to enforce this.
Creating a default thread pool
parallelProcessing
option, using the parallelProcessing()
sub-clause, in the Java DSL, or the parallelProcessing
attribute, in the XML DSL.
from("direct:start") .multicast().parallelProcessing() .to("mock:first") .to("mock:second") .to("mock:third");
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <multicast parallelProcessing="true"> <to uri="mock:first"/> <to uri="mock:second"/> <to uri="mock:third"/> </multicast> </route> </camelContext>
Default thread pool profile settings
Thread Option | Default Value |
---|---|
maxQueueSize | 1000 |
poolSize | 10 |
maxPoolSize | 20 |
keepAliveTime | 60 (seconds) |
rejectedPolicy | CallerRuns |
Changing the default thread pool profile
poolSize
option and the maxQueueSize
option in the default thread pool profile, as follows:
// Java import org.apache.camel.spi.ExecutorServiceManager; import org.apache.camel.spi.ThreadPoolProfile; ... ExecutorServiceManager manager = context.getExecutorServiceManager(); ThreadPoolProfile defaultProfile = manager.getDefaultThreadPoolProfile(); // Now, customize the profile settings. defaultProfile.setPoolSize(3); defaultProfile.setMaxQueueSize(100); ...
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
<threadPoolProfile
id="changedProfile"
defaultProfile="true"
poolSize="3"
maxQueueSize="100"/>
...
</camelContext>
defaultProfile
attribute to true
in the preceding XML DSL example, otherwise the thread pool profile would be treated like a custom thread pool profile (see the section called “Creating a custom thread pool profile”), instead of replacing the default thread pool profile.
Customizing a processor's thread pool
executorService
or executorServiceRef
options (where these options are used instead of the parallelProcessing
option). There are two approaches you can use to customize a processor's thread pool, as follows:
- Specify a custom thread pool—explicitly create an
ExecutorService
(thread pool) instance and pass it to theexecutorService
option. - Specify a custom thread pool profile—create and register a custom thread pool factory. When you reference this factory using the
executorServiceRef
option, the processor automatically uses the factory to create a custom thread pool instance.
executorServiceRef
option, the threading-aware processor first tries to find a custom thread pool with that ID in the registry. If no thread pool is registered with that ID, the processor then attempts to look up a custom thread pool profile in the registry and uses the custom thread pool profile to instantiate a custom thread pool.
Creating a custom thread pool
- Use the
org.apache.camel.builder.ThreadPoolBuilder
utility to build the thread pool class. - Use the
org.apache.camel.spi.ExecutorServiceManager
instance from the currentCamelContext
to create the thread pool class.
ThreadPoolBuilder
is actually defined using the ExecutorServiceManager
instance. Normally, the ThreadPoolBuilder
is preferred, because it offers a simpler approach. But there is at least one kind of thread (the ScheduledExecutorService
) that can only be created by accessing the ExecutorServiceManager
instance directory.
ThreadPoolBuilder
class, which you can set when defining a new custom thread pool.
Builder Option | Description |
---|---|
maxQueueSize() | Sets the maximum number of pending tasks that this thread pool can store in its incoming task queue. A value of -1 specifies an unbounded queue. Default value is taken from default thread pool profile. |
poolSize() | Sets the minimum number of threads in the pool (this is also the initial pool size). Default value is taken from default thread pool profile. |
maxPoolSize() | Sets the maximum number of threads that can be in the pool. Default value is taken from default thread pool profile. |
keepAliveTime() | If any threads are idle for longer than this period of time (specified in seconds), they are terminated. This allows the thread pool to shrink when the load is light. Default value is taken from default thread pool profile. |
rejectedPolicy() |
Specifies what course of action to take, if the incoming task queue is full. You can specify four possible values:
|
build() | Finishes building the custom thread pool and registers the new thread pool under the ID specified as the argument to build() . |
ThreadPoolBuilder
, as follows:
// Java import org.apache.camel.builder.ThreadPoolBuilder; import java.util.concurrent.ExecutorService; ... ThreadPoolBuilder poolBuilder = new ThreadPoolBuilder(context); ExecutorService customPool = poolBuilder.poolSize(5).maxPoolSize(5).maxQueueSize(100).build("customPool"); ... from("direct:start") .multicast().executorService(customPool) .to("mock:first") .to("mock:second") .to("mock:third");
customPool
, directly to the executorService()
option, you can look up the thread pool in the registry, by passing its bean ID to the executorServiceRef()
option, as follows:
// Java from("direct:start") .multicast().executorServiceRef("customPool") .to("mock:first") .to("mock:second") .to("mock:third");
ThreadPoolBuilder
using the threadPool
element. You can then reference the custom thread pool using the executorServiceRef
attribute to look up the thread pool by ID in the Spring registry, as follows:
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <threadPool id="customPool" poolSize="5" maxPoolSize="5" maxQueueSize="100" /> <route> <from uri="direct:start"/> <multicast executorServiceRef="customPool"> <to uri="mock:first"/> <to uri="mock:second"/> <to uri="mock:third"/> </multicast> </route> </camelContext>
Creating a custom thread pool profile
customProfile
, and reference it from within a route, as follows:
// Java import org.apache.camel.spi.ThreadPoolProfile; import org.apache.camel.impl.ThreadPoolProfileSupport; ... // Create the custom thread pool profile ThreadPoolProfile customProfile = new ThreadPoolProfileSupport("customProfile"); customProfile.setPoolSize(5); customProfile.setMaxPoolSize(5); customProfile.setMaxQueueSize(100); context.getExecutorServiceManager().registerThreadPoolProfile(customProfile); ... // Reference the custom thread pool profile in a route from("direct:start") .multicast().executorServiceRef("customProfile") .to("mock:first") .to("mock:second") .to("mock:third");
threadPoolProfile
element to create a custom pool profile (where you let the defaultProfile
option default to false
, because this is not a default thread pool profile). You can create a custom thread pool profile with the bean ID, customProfile
, and reference it from within a route, as follows:
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <threadPoolProfile id="customProfile" poolSize="5" maxPoolSize="5" maxQueueSize="100" /> <route> <from uri="direct:start"/> <multicast executorServiceRef="customProfile"> <to uri="mock:first"/> <to uri="mock:second"/> <to uri="mock:third"/> </multicast> </route> </camelContext>
Sharing a thread pool between components
scheduledExecutorService
property, which you can use to specify the component's ExecutorService
object.
Customizing thread names
setThreadNamePattern
method on the ExecutorServiceStrategy
class or the ExecutorServiceManager
class. Alternatively, an easier way to set the thread name pattern is to set the threadNamePattern
property on the CamelContext
object.
#camelId#
- The name of the current
CamelContext
. #counter#
- A unique thread identifier, implemented as an incrementing counter.
#name#
- The regular Camel thread name.
#longName#
- The long thread name—which can include endpoint parameters and so on.
Camel (#camelId#) thread #counter# - #name#
threadNamePattern
attribute on a Camel context using XML DSL:
<camelContext xmlns="http://camel.apache.org/schema/spring"
threadNamePattern="Riding the thread #counter#" >
<route>
<from uri="seda:start"/>
<to uri="log:result"/>
<to uri="mock:result"/>
</route>
</camelContext>
2.9. Controlling Start-Up and Shutdown of Routes
Overview
CamelContext
instance) starts up and routes are automatically shut down when your Apache Camel application shuts down. For non-critical deployments, the details of the shutdown sequence are usually not very important. But in a production environment, it is often crucial that existing tasks should run to completion during shutdown, in order to avoid data loss. You typically also want to control the order in which routes shut down, so that dependencies are not violated (which would prevent existing tasks from running to completion).
Setting the route ID
myCustomerRouteId
, to a route by invoking the routeId()
command as follows:
from("SourceURI").routeId("myCustomRouteId").process(...).to(TargetURI);
route
element's id
attribute, as follows:
<camelContext id="CamelContextID" xmlns="http://camel.apache.org/schema/spring">
<route id="myCustomRouteId" >
<from uri="SourceURI"/>
<process ref="someProcessorId"/>
<to uri="TargetURI"/>
</route>
</camelContext>
Disabling automatic start-up of routes
autoStartup
command, either with a boolean
argument (true
or false
) or a String
argument (true
or false
). For example, you can disable automatic start-up of a route in the Java DSL, as follows:
from("SourceURI") .routeId("nonAuto") .autoStartup(false) .to(TargetURI);
autoStartup
attribute to false
on the route
element, as follows:
<camelContext id="CamelContextID" xmlns="http://camel.apache.org/schema/spring"> <route id="nonAuto" autoStartup="false"> <from uri="SourceURI"/> <to uri="TargetURI"/> </route> </camelContext>
Manually starting and stopping routes
startRoute()
and stopRoute()
methods on the CamelContext
instance. For example, to start the route having the route ID, nonAuto
, invoke the startRoute()
method on the CamelContext
instance, context
, as follows:
// Java context.startRoute("nonAuto");
nonAuto
, invoke the stopRoute()
method on the CamelContext
instance, context
, as follows:
// Java context.stopRoute("nonAuto");
Startup order of routes
startupOrder()
command, which takes a positive integer value as its argument. The route with the lowest integer value starts first, followed by the routes with successively higher startup order values.
seda:buffer
endpoint. You can ensure that the first route segment starts after the second route segment by assigning startup orders (2 and 1 respectively), as follows:
Example 2.5. Startup Order in Java DSL
from("jetty:http://fooserver:8080") .routeId("first") .startupOrder(2) .to("seda:buffer"); from("seda:buffer") .routeId("second") .startupOrder(1) .to("mock:result"); // This route's startup order is unspecified from("jms:queue:foo").to("jms:queue:bar");
route
element's startupOrder
attribute, as follows:
Example 2.6. Startup Order in XML DSL
<route id="first" startupOrder="2"> <from uri="jetty:http://fooserver:8080"/> <to uri="seda:buffer"/> </route> <route id="second" startupOrder="1"> <from uri="seda:buffer"/> <to uri="mock:result"/> </route> <!-- This route's startup order is unspecified --> <route> <from uri="jms:queue:foo"/> <to uri="jms:queue:bar"/> </route>
Shutdown sequence
CamelContext
instance is shutting down, Apache Camel controls the shutdown sequence using a pluggable shutdown strategy. The default shutdown strategy implements the following shutdown sequence:
- Routes are shut down in the reverse of the start-up order.
- Normally, the shutdown strategy waits until the currently active exchanges have finshed processing. The treatment of running tasks is configurable, however.
- Overall, the shutdown sequence is bound by a timeout (default, 300 seconds). If the shutdown sequence exceeds this timeout, the shutdown strategy will force shutdown to occur, even if some tasks are still running.
Shutdown order of routes
startupOrder()
command (in Java DSL) or startupOrder
attribute (in XML DSL), the first route to shut down is the route with the highest integer value assigned by the start-up order and the last route to shut down is the route with the lowest integer value assigned by the start-up order.
first
, and the second route segment to be shut down is the route with the ID, second
. This example illustrates a general rule, which you should observe when shutting down routes: the routes that expose externally-accessible consumer endpoints should be shut down first, because this helps to throttle the flow of messages through the rest of the route graph.
shutdownRoute(Defer)
, which enables you to specify that a route must be amongst the last routes to shut down (overriding the start-up order value). But you should rarely ever need this option. This option was mainly needed as a workaround for earlier versions of Apache Camel (prior to 2.3), for which routes would shut down in the same order as the start-up order.
Shutting down running tasks in a route
shutdownRunningTask
option, which can take either of the following values:
-
ShutdownRunningTask.CompleteCurrentTaskOnly
- (Default) Usually, a route operates on just a single message at a time, so you can safely shut down the route after the current task has completed.
-
ShutdownRunningTask.CompleteAllTasks
- Specify this option in order to shut down batch consumers gracefully. Some consumer endpoints (for example, File, FTP, Mail, iBATIS, and JPA) operate on a batch of messages at a time. For these endpoints, it is more appropriate to wait until all of the messages in the current batch have completed.
CompleteAllTasks
option, as shown in the following Java DSL fragment:
// Java
public void configure() throws Exception {
from("file:target/pending")
.routeId("first").startupOrder(2)
.shutdownRunningTask(ShutdownRunningTask.CompleteAllTasks)
.delay(1000).to("seda:foo");
from("seda:foo")
.routeId("second").startupOrder(1)
.to("mock:bar");
}
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
<!-- let this route complete all its pending messages when asked to shut down -->
<route id="first"
startupOrder="2"
shutdownRunningTask="CompleteAllTasks">
<from uri="file:target/pending"/>
<delay><constant>1000</constant></delay>
<to uri="seda:foo"/>
</route>
<route id="second" startupOrder="1">
<from uri="seda:foo"/>
<to uri="mock:bar"/>
</route>
</camelContext>
Shutdown timeout
setTimeout()
method on the shutdown strategy. For example, you can change the timeout value to 600 seconds, as follows:
// Java // context = CamelContext instance context.getShutdownStrategy().setTimeout(600);
Integration with custom components
org.apache.camel.Service
interface), you can ensure that your custom code receives a shutdown notification by implementing the org.apache.camel.spi.ShutdownPrepared
interface. This gives the component an opportunity execute custom code in preparation for shutdown.
2.10. Scheduled Route Policy
2.10.1. Overview of Scheduled Route Policies
Overview
Scheduling tasks
- Start a route—start the route at the time (or times) specified. This event only has an effect, if the route is currently in a stopped state, awaiting activation.
- Stop a route—stop the route at the time (or times) specified. This event only has an effect, if the route is currently active.
- Suspend a route—temporarily de-activate the consumer endpoint at the start of the route (as specified in
from()
). The rest of the route is still active, but clients will not be able to send new messages into the route. - Resume a route—re-activate the consumer endpoint at the start of the route, returning the route to a fully active state.
Quartz component
2.10.2. Simple Scheduled Route Policy
Overview
org.apache.camel.routepolicy.quartz.SimpleScheduledRoutePolicy
Dependency
camel-quartz
. For example, if you are using Maven as your build system, you would need to add a dependency on the camel-quartz
artifact.
Java DSL example
startTime
, is defined to be 3 seconds after the current time. The policy is also configured to start the route a second time, 3 seconds after the initial start time, which is configured by setting routeStartRepeatCount
to 1 and routeStartRepeatInterval
to 3000 milliseconds.
routePolicy()
DSL command in the route.
Example 2.7. Java DSL Example of Simple Scheduled Route
// Java
SimpleScheduledRoutePolicy policy = new SimpleScheduledRoutePolicy();
long startTime = System.currentTimeMillis() + 3000L;
policy.setRouteStartDate(new Date(startTime));
policy.setRouteStartRepeatCount(1);
policy.setRouteStartRepeatInterval(3000);
from("direct:start")
.routeId("test")
.routePolicy(policy)
.to("mock:success");
routePolicy()
with multiple arguments.
XML DSL example
routePolicyRef
attribute on the route
element.
Example 2.8. XML DSL Example of Simple Scheduled Route
<bean id="date" class="java.util.Data"/>
<bean id="startPolicy" class="org.apache.camel.routepolicy.quartz.SimpleScheduledRoutePolicy">
<property name="routeStartDate" ref="date"/>
<property name="routeStartRepeatCount" value="1"/>
<property name="routeStartRepeatInterval" value="3000"/>
</bean>
<camelContext xmlns="http://camel.apache.org/schema/spring">
<route id="myroute" routePolicyRef="startPolicy">
<from uri="direct:start"/>
<to uri="mock:success"/>
</route>
</camelContext>
routePolicyRef
as a comma-separated list of bean IDs.
Defining dates and times
java.util.Date
type.The most flexible way to define a Date
instance is through the java.util.GregorianCalendar class. Use the convenient constructors and methods of the GregorianCalendar
class to define a date and then obtain a Date
instance by calling GregorianCalendar.getTime()
.
GregorianCalendar
constructor as follows:
// Java import java.util.GregorianCalendar; import java.util.Calendar; ... GregorianCalendar gc = new GregorianCalendar( 2011, Calendar.JANUARY, 1, 12, // hourOfDay 0, // minutes 0 // seconds ); java.util.Date triggerDate = gc.getTime();
GregorianCalendar
class also supports the definition of times in different time zones. By default, it uses the local time zone on your computer.
Graceful shutdown
Logging Inflight Exchanges on Timeout
org.apache.camel.impl.DefaultShutdownStrategy
, then it logs the same inflight exchange information.
2015-01-12 13:23:23,656 [- ShutdownTask] INFO DefaultShutdownStrategy - There are 1 inflight exchanges: InflightExchange: [exchangeId=ID-davsclaus-air-62213-1421065401253-0-3, fromRouteId=route1, routeId=route1, nodeId=delay1, elapsed=2007, duration=2017]
context.getShutdownStrategegy().setLogInflightExchangesOnTimeout(false);
Scheduling tasks
Starting a route
Parameter | Type | Default | Description |
---|---|---|---|
routeStartDate | java.util.Date | None | Specifies the date and time when the route is started for the first time. |
routeStartRepeatCount | int | 0 | When set to a non-zero value, specifies how many times the route should be started. |
routeStartRepeatInterval | long | 0 | Specifies the time interval between starts, in units of milliseconds. |
Stopping a route
Parameter | Type | Default | Description |
---|---|---|---|
routeStopDate | java.util.Date | None | Specifies the date and time when the route is stopped for the first time. |
routeStopRepeatCount | int | 0 | When set to a non-zero value, specifies how many times the route should be stopped. |
routeStopRepeatInterval | long | 0 | Specifies the time interval between stops, in units of milliseconds. |
routeStopGracePeriod | int | 10000 | Specifies how long to wait for the current exchange to finish processing (grace period) before forcibly stopping the route. Set to 0 for an infinite grace period. |
routeStopTimeUnit | long | TimeUnit.MILLISECONDS | Specifies the time unit of the grace period. |
Suspending a route
Parameter | Type | Default | Description |
---|---|---|---|
routeSuspendDate | java.util.Date | None | Specifies the date and time when the route is suspended for the first time. |
routeSuspendRepeatCount | int | 0 | When set to a non-zero value, specifies how many times the route should be suspended. |
routeSuspendRepeatInterval | long | 0 | Specifies the time interval between suspends, in units of milliseconds. |
Resuming a route
Parameter | Type | Default | Description |
---|---|---|---|
routeResumeDate | java.util.Date | None | Specifies the date and time when the route is resumed for the first time. |
routeResumeRepeatCount | int | 0 | When set to a non-zero value, specifies how many times the route should be resumed. |
routeResumeRepeatInterval | long | 0 | Specifies the time interval between resumes, in units of milliseconds. |
2.10.3. Cron Scheduled Route Policy
Overview
org.apache.camel.routepolicy.quartz.CronScheduledRoutePolicy
Dependency
camel-quartz
. For example, if you are using Maven as your build system, you would need to add a dependency on the camel-quartz
artifact.
Java DSL example
*/3 * * * * ?
, which triggers a start event every 3 seconds.
routePolicy()
DSL command in the route.
Example 2.9. Java DSL Example of a Cron Scheduled Route
// Java CronScheduledRoutePolicy policy = new CronScheduledRoutePolicy(); policy.setRouteStartTime("*/3 * * * * ?"); from("direct:start") .routeId("test") .routePolicy(policy) .to("mock:success");;
routePolicy()
with multiple arguments.
XML DSL example
routePolicyRef
attribute on the route
element.
Example 2.10. XML DSL Example of a Cron Scheduled Route
<bean id="date" class="org.apache.camel.routepolicy.quartz.SimpleDate"/> <bean id="startPolicy" class="org.apache.camel.routepolicy.quartz.CronScheduledRoutePolicy"> <property name="routeStartTime" value="*/3 * * * * ?"/> </bean> <camelContext xmlns="http://camel.apache.org/schema/spring"> <route id="testRoute" routePolicyRef="startPolicy"> <from uri="direct:start"/> <to uri="mock:success"/> </route> </camelContext>
routePolicyRef
as a comma-separated list of bean IDs.
Defining cron expressions
cron
utility, which schedules jobs to run in the background on a UNIX system. A cron expression is effectively a syntax for wildcarding dates and times that enables you to specify either a single event or multiple events that recur periodically.
Seconds Minutes Hours DayOfMonth Month DayOfWeek [Year]
Year
field is optional and usually omitted, unless you want to define an event that occurs once and once only. Each field consists of a mixture of literals and special characters. For example, the following cron expression specifies an event that fires once every day at midnight:
0 0 24 * * ?
*
character is a wildcard that matches every value of a field. Hence, the preceding expression matches every day of every month. The ?
character is a dummy placeholder that means ignore this field. It always appears either in the DayOfMonth
field or in the DayOfWeek
field, because it is not logically consistent to specify both of these fields at the same time. For example, if you want to schedule an event that fires once a day, but only from Monday to Friday, use the following cron expression:
0 0 24 ? * MON-FRI
MON-FRI
. You can also use the forward slash character, /
, to specify increments. For example, to specify that an event fires every 5 minutes, use the following cron expression:
0 0/5 * * * ?
Scheduling tasks
Starting a route
Parameter | Type | Default | Description |
---|---|---|---|
routeStartString | String | None | Specifies a cron expression that triggers one or more route start events. |
Stopping a route
Parameter | Type | Default | Description |
---|---|---|---|
routeStopTime | String | None | Specifies a cron expression that triggers one or more route stop events. |
routeStopGracePeriod | int | 10000 | Specifies how long to wait for the current exchange to finish processing (grace period) before forcibly stopping the route. Set to 0 for an infinite grace period. |
routeStopTimeUnit | long | TimeUnit.MILLISECONDS | Specifies the time unit of the grace period. |
Suspending a route
Parameter | Type | Default | Description |
---|---|---|---|
routeSuspendTime | String | None | Specifies a cron expression that triggers one or more route suspend events. |
Resuming a route
Parameter | Type | Default | Description |
---|---|---|---|
routeResumeTime | String | None | Specifies a cron expression that triggers one or more route resume events. |
2.10.4. Route Policy Factory
Using Route Policy Factory
org.apache.camel.spi.RoutePolicyFactory
as a factory for creating a RoutePolicy
instance for each route. This can be used when you want to use the same kind of route policy for every route. Then you need to only configure the factory once, and every route created will have the policy assigned.
context.addRoutePolicyFactory(new MyRoutePolicyFactory());
<bean>
with the factory
<bean id="myRoutePolicyFactory" class="com.foo.MyRoutePolicyFactory"/>
/** * Creates a new {@link org.apache.camel.spi.RoutePolicy} which will be assigned to the given route. * * @param camelContext the camel context * @param routeId the route id * @param route the route definition * @return the created {@link org.apache.camel.spi.RoutePolicy}, or <tt>null</tt> to not use a policy for this route */ RoutePolicy createRoutePolicy(CamelContext camelContext, String routeId, RouteDefinition route);
addRoutePolicyFactory
again, or declare the other factories as <bean>
in XML.
2.11. Metrics
Overview
- Add camel-metrics component
- Enable route metrics in XML or Java code
Metrics Route Policy
MetricsRoutePolicy
on a per route basis.
MetricsRoutePolicy
to be assigned as the route's policy. This is shown below:
from("file:src/data?noop=true").routePolicy(new MetricsRoutePolicy()).to("jms:incomingOrders");
<bean>
which is specified as the route's policy; for example:
<bean id="policy" class="org.apache.camel.component.metrics.routepolicy.MetricsRoutePolicy"/> <camelContext xmlns="http://camel.apache.org/schema/spring"> <route routePolicyRef="policy"> <from uri="file:src/data?noop=true"/> [...]
Metrics Route Policy Factory
RoutePolicy
for each route which exposes route utilization statistics using Codahale metrics. This factory can be used in Java and XML as the examples below demonstrate.
CamelContext
as shown below:
context.addRoutePolicyFactory(new MetricsRoutePolicyFactory());
<bean>
as follows:
<!-- use camel-metrics route policy to gather metrics for all routes --> <bean id="metricsRoutePolicyFactory" class="org.apache.camel.component.metrics.routepolicy.MetricsRoutePolicyFactory"/>
com.codahale.metrics.MetricRegistry
from the org.apache.camel.component.metrics.routepolicy.MetricsRegistryService
as shown below:
MetricRegistryService registryService = context.hasService(MetricsRegistryService.class); if (registryService != null) { MetricsRegistry registry = registryService.getMetricsRegistry(); ... }
Options
MetricsRoutePolicyFactory
and MetricsRoutePolicy
supports the following options:
Name | Default | Description |
---|---|---|
durationUnit
|
TimeUnit.MILLISECONDS
|
The unit to use for duration in the metrics reporter or when dumping the statistics as json. |
jmxDomain
|
org.apache.camel.metrics
|
The JXM domain name. |
metricsRegistry
|
Allow to use a shared com.codahale.metrics.MetricRegistry . If none is provided then Camel will create a shared instance used by the this CamelContext.
|
|
prettyPrint
|
false
|
Whether to use pretty print when outputting statistics in json format. |
rateUnit
|
TimeUnit.SECONDS
|
The unit to use for rate in the metrics reporter or when dumping the statistics as json. |
useJmx
|
false
|
Whether to report fine grained statistics to JMX by using the
com.codahale.metrics.JmxReporter .
Notice that if JMX is enabled on CamelContext then a
MetricsRegistryService mbean is enlisted under the services type in the JMX tree. That mbean has a single operation to output the statistics using json. Setting useJmx to true is only needed if you want fine grained mbeans per statistics type.
|
2.12. JMX Naming
Overview
CamelContext
bean as it appears in JMX, by defining a management name pattern for it. For example, you can customise the name pattern of an XML CamelContext
instance, as follows:
<camelContext id="myCamel" managementNamePattern="#name#">
...
</camelContext>
CamelContext
bean, Apache Camel reverts to a default naming strategy.
Default naming strategy
CamelContext
bean deployed in an OSGi bundle is equal to the OSGi symbolic name of the bundle. For example, if the OSGi symbolic name is MyCamelBundle
, the JMX name would be MyCamelBundle
. In cases where there is more than one CamelContext
in the bundle, the JMX name is disambiguated by adding a counter value as a suffix. For example, if there are multiple Camel contexts in the MyCamelBundle
bundle, the corresponding JMX MBeans are named as follows:
MyCamelBundle-1 MyCamelBundle-2 MyCamelBundle-3 ...
Customising the JMX naming strategy
CamelContext
bean will have the same JMX name between runs. If you want to have greater consistency between runs, you can control the JMX name more precisely by defining a JMX name pattern for the CamelContext
instances.
Specifying a name pattern in Java
CamelContext
in Java, call the setNamePattern
method, as follows:
// Java context.getManagementNameStrategy().setNamePattern("#name#");
Specifying a name pattern in XML
CamelContext
in XML, set the managementNamePattern
attribute on the camelContext
element, as follows:
<camelContext id="myCamel" managementNamePattern="#name#">
Name pattern tokens
Token | Description |
---|---|
#camelId# | Value of the id attribute on the CamelContext bean. |
#name# | Same as #camelId# . |
#counter# | An incrementing counter (starting at 1 ). |
#bundleId# | The OSGi bundle ID of the deployed bundle (OSGi only). |
#symbolicName# | The OSGi symbolic name (OSGi only). |
#version# | The OSGi bundle version (OSGi only). |
Examples
<camelContext id="fooContext" managementNamePattern="FooApplication-#name#"> ... </camelContext> <camelContext id="myCamel" managementNamePattern="#bundleID#-#symbolicName#-#name#"> ... </camelContext>
Ambiguous names
<camelContext id="foo" managementNamePattern="SameOldSameOld"> ... </camelContext> ... <camelContext id="bar" managementNamePattern="SameOldSameOld"> ... </camelContext>
2.13. Performance and Optimization
Avoid unnecessary message copying
allowUseOriginalMessage
option to false
on the CamelContext
object. For example, in Blueprint XML you can set this option as follows:
<camelContext xmlns="http://camel.apache.org/schema/blueprint"
allowUseOriginalMessage="false">
...
</camelContext>
allowUseOriginalMessage
to false
, if the following conditions are satisfied:
- You do not set
useOriginalMessage=true
on any of the error handlers or on theonException
element. - You do not use the
getOriginalMessage
method anywhere in your Java application code.
Chapter 3. Introducing Enterprise Integration Patterns
Abstract
3.1. Overview of the Patterns
Enterprise Integration Patterns book
Messaging systems
Icon | Name | Use Case |
---|---|---|
Message | How can two applications connected by a message channel exchange a piece of information? | |
Message Channel | How does one application communicate with another application using messaging? | |
Message Endpoint | How does an application connect to a messaging channel to send and receive messages? | |
Pipes and Filters | How can we perform complex processing on a message while still maintaining independence and flexibility? | |
Message Router | How can you decouple individual processing steps so that messages can be passed to different filters depending on a set of defined conditions? | |
Message Translator | How do systems using different data formats communicate with each other using messaging? |
Messaging channels
Icon | Name | Use Case |
---|---|---|
Point to Point Channel | How can the caller be sure that exactly one receiver will receive the document or will perform the call? | |
Publish Subscribe Channel | How can the sender broadcast an event to all interested receivers? | |
Dead Letter Channel | What will the messaging system do with a message it cannot deliver? | |
Guaranteed Delivery | How does the sender make sure that a message will be delivered, even if the messaging system fails? | |
Message Bus | What is an architecture that enables separate, decoupled applications to work together, such that one or more of the applications can be added or removed without affecting the others? |
Message construction
Icon | Name | Use Case |
---|---|---|
Correlation Identifier | How does a requestor identify the request that generated the received reply? | |
Return Address | How does a replier know where to send the reply? |
Message routing
Icon | Name | Use Case |
---|---|---|
Content Based Router | How do we handle a situation where the implementation of a single logical function (e.g., inventory check) is spread across multiple physical systems? | |
Message Filter | How does a component avoid receiving uninteresting messages? | |
Recipient List | How do we route a message to a list of dynamically specified recipients? | |
Splitter | How can we process a message if it contains multiple elements, each of which might have to be processed in a different way? | |
Aggregator | How do we combine the results of individual, but related messages so that they can be processed as a whole? | |
Resequencer | How can we get a stream of related, but out-of-sequence, messages back into the correct order? | |
Composed Message Processor | How can you maintain the overall message flow when processing a message consisting of multiple elements, each of which may require different processing? | |
Scatter-Gather | How do you maintain the overall message flow when a message needs to be sent to multiple recipients, each of which may send a reply? | |
Routing Slip | How do we route a message consecutively through a series of processing steps when the sequence of steps is not known at design-time, and might vary for each message? | |
Throttler | How can I throttle messages to ensure that a specific endpoint does not get overloaded, or that we don't exceed an agreed SLA with some external service? | |
Delayer | How can I delay the sending of a message? | |
Load Balancer | How can I balance load across a number of endpoints? | |
Multicast | How can I route a message to a number of endpoints at the same time? | |
Loop | How can I repeat processing a message in a loop? | |
Sampling | How can I sample one message out of many in a given period to avoid downstream route does not get overloaded? |
Message transformation
Icon | Name | Use Case |
---|---|---|
Content Enricher | How do we communicate with another system if the message originator does not have all the required data items available? | |
Content Filter | How do you simplify dealing with a large message, when you are interested in only a few data items? | |
Claim Check | How can we reduce the data volume of message sent across the system without sacrificing information content? | |
Normalizer | How do you process messages that are semantically equivalent, but arrive in a different format? | |
Sort | How can I sort the body of a message? |
Messaging endpoints
Icon | Name | Use Case |
---|---|---|
Messaging Mapper | How do you move data between domain objects and the messaging infrastructure while keeping the two independent of each other? | |
Event Driven Consumer | How can an application automatically consume messages as they become available? | |
Polling Consumer | How can an application consume a message when the application is ready? | |
Competing Consumers | How can a messaging client process multiple messages concurrently? | |
Message Dispatcher | How can multiple consumers on a single channel coordinate their message processing? | |
Selective Consumer | How can a message consumer select which messages it wants to receive? | |
Durable Subscriber | How can a subscriber avoid missing messages when it's not listening for them? | |
Idempotent Consumer | How can a message receiver deal with duplicate messages? | |
Transactional Client | How can a client control its transactions with the messaging system? | |
Messaging Gateway | How do you encapsulate access to the messaging system from the rest of the application? | |
Service Activator | How can an application design a service to be invoked both via various messaging technologies and via non-messaging techniques? |
System management
Icon | Name | Use Case |
---|---|---|
Wire Tap | How do you inspect messages that travel on a point-to-point channel? |
Chapter 4. Defining REST Services
Abstract
4.1. Overview of REST in Camel
Overview
What is REST?
GET
, POST
, PUT
, and DELETE
.
A sample REST invocation
localhost:9091
, you could navigate to a URL like the following in your browser:
http://localhost:9091/say/hello/Garp
Hello Garp
curl
command-line utility), is one of the many reasons why the REST protocol has rapidly gained popularity.
REST wrapper layers
- REST DSL
- The REST DSL (in
camel-core
) is a facade or wrapper layer that provides a simplified builder API for defining REST services. The REST DSL does not itself provide a REST implementation: it must be combined with an underlying REST implementation. For example, the following Java code shows how to define a simple Hello World service using the REST DSL:rest("/say") .get("/hello/{name}").route().transform().simple("Hello ${header.name}");
For more details, see Section 4.2, “Defining Services with REST DSL”. - Rest component
- The Rest component (in
camel-core
) is a wrapper layer that enables you to define REST services using a URI syntax. Like the REST DSL, the Rest component does not itself provide a REST implementation: it must be combined with an underlying REST implementation. For example, the following Java code shows how to define a simple Hello World service using the Rest component:from("rest:get:say:/hello/{name}").transform().simple("Hello ${header.name}");
For more details, see Rest.
REST implementations
- Restlet component
- The Restlet component (in
camel-restlet
) is a REST implementation that can, in principle, be layered above different transport protocols (although this component is only tested against the HTTP protocol). This component also provides an integration with the Restlet Framework, which is a commercial framework for developing REST services in Java. For example, the following Java code shows how to define a simple Hello World service using the Restlet component:from("restlet:http://0.0.0.0:9091/say/hello/{name}?restletMethod=get") .transform().simple("Hello ${header.name}");
For more details, see Restlet. - Servlet component
- The Servlet component (in
camel-servlet
) is a component that binds a Java servlet to a Camel route. In other words, the Servlet component enables you to package and deploy a Camel route as if it was a standard Java servlet. The Servlet component is therefore particularly useful, if you need to deploy a Camel route inside a servlet container (for example, into an Apache Tomcat HTTP server or into a JBoss Enterprise Application Platform container).The Servlet component on its own, however, does not provide any convenient REST API for defining REST services. The easiest way to use the Servlet component, therefore, is to combine it with the REST DSL, so that you can define REST services with a user-friendly API.For more details, see Servlet.
JAX-RS REST implementation
- @Path
- Annotation that can map a context path to a Java class or map a sub-path to a particular Java method.
- @GET, @POST, @PUT, @DELETE
- Annotations that map a HTTP method to a Java method.
- @PathParam
- Annotation that either maps a URI parameter to a Java method argument, or injects a URI parameter into a field.
- @QueryParam
- Annotation that either maps a query parameter to a Java method argument, or injects a query parameter into a field.
4.2. Defining Services with REST DSL
REST DSL is a facade
Advantages of the REST DSL
- A modern easy-to-use syntax for defining REST services.
- Compatible with multiple different Apache Camel components.
- Swagger integration (through the
camel-swagger
component).
Components that integrate with REST DSL
- Servlet component (
camel-servlet
). - Netty HTTP component (
camel-netty-http
). - Netty4 HTTP component (
camel-netty4-http
). - Jetty component (
camel-jetty
). - Restlet component (
camel-restlet
).
camel-core
) is not a REST implementation. Like the REST DSL, the Rest component is a facade, providing a simplified syntax to define REST services using a URI syntax. The Rest component also requires an underlying REST implementation.
Configuring REST DSL to use a REST implementation
restConfiguration()
builder (in Java DSL) or the restConfiguration
element (in XML DSL). For example, to configure REST DSL to use the Restlet component, you would use a builder expression like the following in the Java DSL:
restConfiguration().component("restlet").port(9091);
camelContext
) in the XML DSL:
<restConfiguration component="restlet" port="9091"/>
Syntax
rest("BasePath").Option()+. .Verb("Path").Option()+.[to() | route().CamelRoute.endRest()] .Verb("Path").Option()+.[to() | route().CamelRoute.endRest()] ... .Verb("Path").Option()+.[to() | route().CamelRoute];
CamelRoute
is an optional embedded Camel route (defined using the standard Java DSL syntax for routes).
rest()
keyword, followed by one or more verb clauses that handle specific URL path segments. The HTTP verb can be one of get()
, head()
, put()
, post()
, delete()
, or verb()
. Each verb clause can use either of the following syntaxes:
- Verb clause ending in
to()
keyword. For example:get("...").Option()+.to("...")
- Verb clause ending in
route()
keyword (for embedding a Camel route). For example:get("...").Option()+.route("...").CamelRoute.endRest()
REST DSL with Java
RouteBuilder.configure()
method, just like you do for regular Apache Camel routes. For example, to define a simple Hello World service using the REST DSL with the Restlet component, define the following Java code:
restConfiguration().component("restlet").port(9091); rest("/say") .get("/hello").to("direct:hello") .get("/bye").to("direct:bye"); from("direct:hello") .transform().constant("Hello World"); from("direct:bye") .transform().constant("Bye World");
-
restConfiguration()
- Configures the REST DSL to use a specific REST implementation (Restlet).
-
rest()
- Defines a service using the REST DSL. Each of the verb clauses are terminated by a
to()
keyword, which forwards the incoming message to adirect
endpoint (thedirect
component splices routes together within the same application). -
from()
- Defines a regular Camel route.
REST DSL with XML
rest
element as a child of the camelContext
element. For example, to define a simple Hello World service using the REST DSL with the Restlet component, define the following XML code (in Blueprint):
<camelContext xmlns="http://camel.apache.org/schema/blueprint"> <restConfiguration component="restlet" port="9091"/> <rest path="/say"> <get uri="/hello"> <to uri="direct:hello"/> </get> <get uri="/bye"> <to uri="direct:bye"/> </get> </rest> <route> <from uri="direct:hello"/> <transform> <constant>Hello World</constant> </transform> </route> <route> <from uri="direct:bye"/> <transform> <constant>Bye World</constant> </transform> </route> </camelContext>
Specifying a base path
rest()
keyword (Java DSL) or the path
attribute of the rest
element (XML DSL) allows you to define a base path, which is then prefixed to the paths in all of the verb clauses. For example, given the following snippet of Java DSL:
rest("/say")
.get("/hello").to("direct:hello")
.get("/bye").to("direct:bye");
<rest path="/say">
<get uri="/hello">
<to uri="direct:hello"/>
</get>
<get uri="/bye" consumes="application/json">
<to uri="direct:bye"/>
</get>
</rest>
/say/hello /say/bye
rest() .get("/say/hello").to("direct:hello") .get("/say/bye").to("direct:bye");
URI templates
rest("/say") .get("/hello/{name}").to("direct:hello") .get("/bye/{name}").to("direct:bye"); from("direct:hello") .transform().simple("Hello ${header.name}"); from("direct:bye") .transform().simple("Bye ${header.name}");
{name}
path segment and copies this captured text into the name
message header. If you invoke the service by sending a GET HTTP Request with the URL ending in /say/hello/Joe
, the HTTP Response is Hello Joe
.
Embedded route syntax
to()
keyword (Java DSL) or the to
element (XML DSL), you have the option of embedding an Apache Camel route directly into the REST DSL, using the route()
keyword (Java DSL) or the route
element (XML DSL). The route()
keyword enables you to embed a route into a verb clause, with the following syntax:
RESTVerbClause.route("...").CamelRoute.endRest()
endRest()
keyword (Java DSL only) is a necessary punctuation mark that enables you to separate the verb clauses (when there is more than one verb clause in the rest()
builder).
rest("/say") .get("/hello").route().transform().constant("Hello World").endRest() .get("/bye").route().transform().constant("Bye World");
<camelContext xmlns="http://camel.apache.org/schema/blueprint"> ... <rest path="/say"> <get uri="/hello"> <route> <transform> <constant>Hello World</constant> </transform> </route> </get> <get uri="/bye"> <route> <transform> <constant>Bye World</constant> </transform> </route> </get> </rest> </camelContext>
onException()
) or interceptors (using intercept()
) in the current CamelContext
, these exception clauses and interceptors are also active in the embedded routes.
Specifying the content type of requests and responses
consumes()
and produces()
options in Java, or the consumes
and produces
attributes in XML. For example, some common content types (officially known as Internet media types) are the following:
text/plain
text/html
text/xml
application/json
application/xml
text/plain
HTTP requests, and to send only text/html
HTTP responses, you would use Java code like the following:
rest("/email") .post("/to/{recipient}").consumes("text/plain").produces("text/html").to("direct:foo");
consumes
and produces
attributes, as follows:
<camelContext xmlns="http://camel.apache.org/schema/blueprint"> ... <rest path="/email"> <post uri="/to/{recipient}" consumes="text/plain" produces="text/html"> <to "direct:foo"/> </get> </rest> </camelContext>
consumes()
or produces()
as a comma-separated list. For example, consumes("text/plain, application/json")
.
Additional HTTP methods
get()
, head()
, put()
, post()
, delete()
. To access additional HTTP methods, you can use the generic keyword, verb()
, in Java DSL and the generic element, verb
, in XML DSL.
rest("/say") .verb("TRACE", "/hello").route().transform();
transform()
copies the body of the IN message to the body of the OUT message, thus echoing the HTTP request.
<camelContext xmlns="http://camel.apache.org/schema/blueprint"> ... <rest path="/say"> <verb uri="/hello" method="TRACE"> <route> <transform/> </route> </get> </camelContext>
Defining custom HTTP error messages
- Specify the HTTP error code by setting the
Exchange.HTTP_RESPONSE_CODE
header key to the error code value (for example,400
,404
, and so on). This setting indicates to the REST DSL that you want to send an error message reply, instead of a regular response. - Populate the message body with your custom error message.
- Set the
Content-Type
header, if required. - If your REST service is configured to marshal to and from Java objects (that is,
bindingMode
is enabled), you should ensure that theskipBindingOnErrorCode
option is enabled (which it is, by default). This is to ensure that the REST DSL does not attempt to unmarshal the message body when sending the response.For more details about object binding, see Section 4.3, “Marshalling to and from Java Objects”.
// Java // Configure the REST DSL, with JSON binding mode restConfiguration().component("restlet").host("localhost").port(portNum).bindingMode(RestBindingMode.json); // Define the service with REST DSL rest("/users/") .post("lives").type(UserPojo.class).outType(CountryPojo.class) .route() .choice() .when().simple("${body.id} < 100") .bean(new UserErrorService(), "idTooLowError") .otherwise() .bean(new UserService(), "livesWhere");
UserErrorService
bean, which is implemented as follows:
// Java public class UserErrorService { public void idTooLowError(Exchange exchange) { exchange.getIn().setBody("id value is too low"); exchange.getIn().setHeader(Exchange.CONTENT_TYPE, "text/plain"); exchange.getIn().setHeader(Exchange.HTTP_RESPONSE_CODE, 400); } }
UserErrorService
bean we define the custom error message and set the HTTP error code to 400
.
Wrapping a JsonParserException in a custom HTTP error message
JsonParserException
exception. For example, you can conveniently exploit the Camel exception handling mechanism to create a custom HTTP error message, with HTTP error code 400, as follows:
// Java onException(JsonParseException.class) .handled(true) .setHeader(Exchange.HTTP_RESPONSE_CODE, constant(400)) .setHeader(Exchange.CONTENT_TYPE, constant("text/plain")) .setBody().constant("Invalid json data");
REST DSL options
rest()
), as follows:
rest("/email").consumes("text/plain").produces("text/html")
.post("/to/{recipient}").to("direct:foo")
.get("/for/{username}").to("direct:bar");
rest("/email") .post("/to/{recipient}").consumes("text/plain").produces("text/html").to("direct:foo") .get("/for/{username}").consumes("text/plain").produces("text/html").to("direct:bar");
Java DSL | XML DSL | Description |
---|---|---|
bindingMode() | @bindingMode | Specifies the binding mode, which can be used to marshal incoming messages to Java objects (and, optionally, unmarshal Java objects to outgoing messages). Can have the following values: off (default), auto , json , xml , json_xml . |
consumes() | @consumes | Restricts the verb clause to accept only the specified Internet media type (MIME type) in a HTTP Request. Typical values are: text/plain , text/http , text/xml , application/json , application/xml . |
customId() | @customId | Defines a custom ID for JMX management. |
description() | description | Document the REST service or verb clause. Useful for JMX management and tooling. |
enableCORS() | @enableCORS | If true , enables CORS (cross-origin resource sharing) headers in the HTTP response. Default is false . |
id() | @id | Defines a unique ID for the REST service, which is useful to define for JMX management and other tooling. |
method() | @method | Specifies the HTTP method processed by this verb clause. Usually used in conjunction with the generic verb() keyword. |
outType() | @outType | When object binding is enabled (that is, when bindingMode option is enabled), this option specifies the Java type that represents a HTTP Response message. |
produces() | produces | Restricts the verb clause to produce only the specified Internet media type (MIME type) in a HTTP Response. Typical values are: text/plain , text/http , text/xml , application/json , application/xml . |
type() | @type | When object binding is enabled (that is, when bindingMode option is enabled), this option specifies the Java type that represents a HTTP Request message. |
VerbURIArgument | @uri | Specifies a path segment or URI template as an argument to a verb. For example, get(VerbURIArgument) . |
BasePathArgument | @path | Specifies the base path in the rest() keyword (Java DSL) or in the rest element (XML DSL). |
4.3. Marshalling to and from Java Objects
Marshalling Java objects for transmission over HTTP
- JSON
- JSON (JavaScript object notation) is a lightweight data format that can easily be mapped to and from Java objects. The JSON syntax is compact, lightly typed, and easy for humans to read and write. For all of these reasons, JSON has become popular as a message format for REST services.For example, the following JSON code could represent a
User
bean with two property fields,id
andname
:{ "id" : 1234, "name" : "Jane Doe" }
- JAXB
- JAXB (Java Architecture for XML Binding) is an XML-based data format that can easily be mapped to and from Java objects. In order to marshal the XML to a Java object, you must also annotate the Java class that you want to use.For example, the following JAXB code could represent a
User
bean with two property fields,id
andname
:<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <User> <Id>1234</Id> <Name>Jane Doe</Name> </User>
Integration of JSON and JAXB with the REST DSL
- Marshalling to and from Java objects is performed automatically (given the appropriate configuration).
- The REST DSL can automatically detect the data format (either JSON or JAXB) and perform the appropriate conversion.
- The REST DSL provides an abstraction layer, so that the code you write is not specific to a particular JSON or JAXB implementation. So you can switch the implementation later on, with minimum impact to your application code.
Supported data format components
- JSON
- Jackson data format (
camel-jackson
) (default) - GSon data format (
camel-gson
) - XStream data format (
camel-xstream
)
- JAXB
- JAXB data format (
camel-jaxb
)
How to enable object marshalling
- Enable binding mode, by setting the
bindingMode
option (there are several levels at which you can set the binding mode—for details, see the section called “Configuring the binding mode”). - Specify the Java type to convert to (or from), on the incoming message with the
type
option (required), and on the outgoing message with theoutType
option (optional). - If you want to convert your Java object to and from the JAXB data format, you must remember to annotate the Java class with the appropriate JAXB annotations.
- Specify the underlying data format implementation (or implementations), using the
jsonDataFormat
option and/or thexmlDataFormat
option (which can be specified on therestConfiguration
builder). - If your route provides a return value in JAXB format, you are normally expected to set the Out message of the exchange body to be an instance of a class with JAXB annotations (a JAXB element). If you prefer to provide the JAXB return value directly in XML format, however, set the
dataFormatProperty
with the key,xml.out.mustBeJAXBElement
, tofalse
(which can be specified on therestConfiguration
builder). For example, in the XML DSL syntax:<restConfiguration ...> <dataFormatProperty key="xml.out.mustBeJAXBElement" value="false"/> ... </restConfiguration>
- Add the required dependencies to your project build file. For example, if you are using the Maven build system and you are using the Jackson data format, you would add the following dependency to your Maven POM file:
<?xml version="1.0" encoding="UTF-8"?> <project ...> ... <dependencies> ... <!-- use for json binding --> <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-jackson</artifactId> </dependency> ... </dependencies> </project>
- When deploying your application to the OSGi container, remember to install the requisite feature for your chosen data format. For example, if you are using the Jackson data format (the default), you would install the
camel-jackson
feature, by entering the following Karaf console command:JBossFuse:karaf@root> features:install camel-jackson
Alternatively, if you are deploying into a Fabric environment, you would add the feature to a Fabric profile. For example, if you are using the profile,MyRestProfile
, you could add the feature by entering the following console command:JBossFuse:karaf@root> fabric:profile-edit --features camel-jackson MyRestProfile
Configuring the binding mode
bindingMode
option is off
by default, so you must configure it explicitly, in order to enable marshalling of Java objects. TABLE shows the list of supported binding modes.
Binding Mode | Description |
---|---|
off |
Binding is turned off (default).
|
auto |
Binding is enabled for JSON and/or XML. In this mode, Camel auto-selects either JSON or XML (JAXB), based on the format of the incoming message. You are not required to enable both kinds of data format, however: either a JSON implementation, an XML implementation, or both can be provided on the classpath.
|
json |
Binding is enabled for JSON only. A JSON implementation must be provided on the classpath (by default, Camel tries to enable the
camel-jackson implementation).
|
xml |
Binding is enabled for XML only. An XML implementation must be provided on the classpath (by default, Camel tries to enable the
camel-jaxb implementation).
|
json_xml |
Binding is enabled for both JSON and XML. In this mode, Camel auto-selects either JSON or XML (JAXB), based on the format of the incoming message. You are required to provide both kinds of data format on the classpath.
|
enum
type:
org.apache.camel.model.rest.RestBindingMode
bindingMode
, as follows:
- REST DSL configuration
- You can set the
bindingMode
option from therestConfiguration
builder, as follows:restConfiguration().component("servlet").port(8181).bindingMode(RestBindingMode.json);
- Service definition base part
- You can set the
bindingMode
option immediately following therest()
keyword (before the verb clauses), as follows:rest("/user").bindingMode(RestBindingMode.json).get("/{id}").VerbClause
- Verb clause
- You can set the
bindingMode
option in a verb clause, as follows:rest("/user") .get("/{id}").bindingMode(RestBindingMode.json).to("...");
Example
camel-example-servlet-rest-blueprint
example. You can find this example by installing the standalone Apache Camel distribution, apache-camel-2.15.1.redhat-620133.zip
, which is provided in the extras/
subdirectory of your JBoss Fuse installation.
ApacheCamelInstallDir/examples/camel-example-servlet-rest-blueprint
Configure the Servlet component as the REST implementation
camel-example-servlet-rest-blueprint
example, the underlying implementation of the REST DSL is provided by the Servlet component. The Servlet component is configured in the Blueprint XML file, as shown in Example 4.1, “Configure Servlet Component for REST DSL”.
Example 4.1. Configure Servlet Component for REST DSL
<?xml version="1.0" encoding="UTF-8"?> <blueprint ...> <!-- to setup camel servlet with OSGi HttpService --> <reference id="httpService" interface="org.osgi.service.http.HttpService"/> <bean class="org.apache.camel.component.servlet.osgi.OsgiServletRegisterer" init-method="register" destroy-method="unregister"> <property name="alias" value="/camel-example-servlet-rest-blueprint/rest"/> <property name="httpService" ref="httpService"/> <property name="servlet" ref="camelServlet"/> </bean> <bean id="camelServlet" class="org.apache.camel.component.servlet.CamelHttpTransportServlet"/> ... <camelContext xmlns="http://camel.apache.org/schema/blueprint"> <restConfiguration component="servlet" bindingMode="json" contextPath="/camel-example-servlet-rest-blueprint/rest" port="8181"> <dataFormatProperty key="prettyPrint" value="true"/> </restConfiguration> ... </camelContext> </blueprint>
- REST DSL layer
- The REST DSL layer is configured by the
restConfiguration
element, which integrates with the Servlet component by setting thecomponent
attribute to the value,servlet
. - Servlet component layer
- The Servlet component layer is implemented as an instance of the class,
CamelHttpTransportServlet
, where the example instance has the bean ID,camelServlet
. - HTTP container layer
- The Servlet component must be deployed into a HTTP container. The Karaf container is normally configured with a default HTTP container (a Jetty HTTP container), which listens for HTTP requests on the port, 8181. To deploy the Servlet component to the default Jetty container, you need to do the following:
- Get an OSGi reference to the
org.osgi.service.http.HttpService
OSGi service, where this service is a standardised OSGi interface that provides access to the default HTTP server in OSGi. - Create an instance of the utility class,
OsgiServletRegisterer
, to register the Servlet component in the HTTP container. TheOsgiServletRegisterer
class is a utility that simplifies managing the lifecycle of the Servlet component. When an instance of this class is created, it automatically calls theregisterServlet
method on theHttpService
OSGi service; and when the instance is destroyed, it automatically calls theunregister
method.
Required dependencies
- Servlet component
- Provides the underlying implementation of the REST DSL. This is specified in the Maven POM file, as follows:
<dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-servlet</artifactId> <version>${camel-version}</version> </dependency>
And before you deploy the application bundle to the OSGi container, you must install the Servlet component feature, as follows:JBossFuse:karaf@root> features:install camel-servlet
- Jackson data format
- Provides the JSON data format implementation. This is specified in the Maven POM file, as follows:
<dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-jackson</artifactId> <version>${camel-version}</version> </dependency>
And before you deploy the application bundle to the OSGi container, you must install the Jackson data format feature, as follows:JBossFuse:karaf@root> features:install camel-jackson
Java type for responses
User
type objects back and forth in HTTP Request and Response messages. The User
Java class is defined as shown in Example 4.2, “User Class for JSON Response”.
Example 4.2. User Class for JSON Response
// Java package org.apache.camel.example.rest; public class User { private int id; private String name; public User() { } public User(int id, String name) { this.id = id; this.name = name; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } }
User
class has a relatively simple representation in the JSON data format. For example, a typical instance of this class expressed in JSON format is:
{ "id" : 1234, "name" : "Jane Doe" }
Sample REST DSL route with JSON binding
Example 4.3. REST DSL Route with JSON Binding
<?xml version="1.0" encoding="UTF-8"?> <blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" ...> ... <!-- a bean for user services --> <bean id="userService" class="org.apache.camel.example.rest.UserService"/> <camelContext xmlns="http://camel.apache.org/schema/blueprint"> <restConfiguration component="servlet" bindingMode="json" contextPath="/camel-example-servlet-rest-blueprint/rest" port="8181"> <dataFormatProperty key="prettyPrint" value="true"/> </restConfiguration> <!-- defines the REST services using the base path, /user --> <rest path="/user" consumes="application/json" produces="application/json"> <description>User rest service</description> <!-- this is a rest GET to view a user with the given id --> <get uri="/{id}" outType="org.apache.camel.example.rest.User"> <description>Find user by id</description> <to uri="bean:userService?method=getUser(${header.id})"/> </get> <!-- this is a rest PUT to create/update a user --> <put type="org.apache.camel.example.rest.User"> <description>Updates or create a user</description> <to uri="bean:userService?method=updateUser"/> </put> <!-- this is a rest GET to find all users --> <get uri="/findAll" outType="org.apache.camel.example.rest.User[]"> <description>Find all users</description> <to uri="bean:userService?method=listUsers"/> </get> </rest> </camelContext> </blueprint>
REST operations
-
GET /camel-example-servlet-rest-blueprint/rest/user/{id}
- Get the details for the user identified by
{id}
, where the HTTP response is returned in JSON format. -
PUT /camel-example-servlet-rest-blueprint/rest/user
- Create a new user, where the user details are contained in the body of the PUT message, encoded in JSON format (to match the
User
object type). -
GET /camel-example-servlet-rest-blueprint/rest/user/findAll
- Get the details for all users, where the HTTP response is returned as an array of users, in JSON format.
URLs to invoke the REST service
-
http://localhost:8181
- In
restConfiguration
, the protocol defaults tohttp
and the port is set explicitly to8181
. -
/camel-example-servlet-rest-blueprint/rest
- Specified by the
contextPath
attribute of therestConfiguration
element. -
/user
- Specified by the
path
attribute of therest
element. -
/{id}
- Specified by the
uri
attribute of theget
verb element.
curl
utility, by entering the following command at the command line:
curl -X GET -H "Accept: application/json" http://localhost:8181/camel-example-servlet-rest-blueprint/rest/user/123
curl
, by entering the following sample commands:
curl -X GET -H "Accept: application/json" http://localhost:8181/camel-example-servlet-rest-blueprint/rest/user/findAll curl -X PUT -d "{ \"id\": 666, \"name\": \"The devil\"}" -H "Accept: application/json" http://localhost:8181/camel-example-servlet-rest-blueprint/rest/user
4.4. Configuring the REST DSL
Configuring with Java
restConfiguration()
builder API. For example, to configure the REST DSL to use the Servlet component as the underlying implementation:
restConfiguration().component("servlet").bindingMode("json").port("8181") .contextPath("/camel-example-servlet-rest-blueprint/rest");
Configuring with XML
restConfiguration
element. For example, to configure the REST DSL to use the Servlet component as the underlying implementation:
<?xml version="1.0" encoding="UTF-8"?> <blueprint ...> ... <camelContext xmlns="http://camel.apache.org/schema/blueprint"> ... <restConfiguration component="servlet" bindingMode="json" contextPath="/camel-example-servlet-rest-blueprint/rest" port="8181"> <dataFormatProperty key="prettyPrint" value="true"/> </restConfiguration> ... </camelContext> </blueprint>
Configuration options
restConfiguration()
builder (Java DSL) or the restConfiguration
element (XML DSL).
Java DSL | XML DSL | Description |
---|---|---|
component() | @component |
Specifies the Camel component to use as the REST transport (for example,
servlet , restlet ,, and so on). The value can either be the standard component name or the bean ID of a custom instance. If this option is not specified, Camel looks for an instance of RestConsumerFactory on the classpath or in the bean registry.
|
scheme() | @scheme |
The protocol to use for exposing the REST service. Depends on the underlying REST implementation, but
http and https are usually supported. Default is http .
|
host() | @host |
The hostname to use for exposing the REST service.
|
port() | @port |
The port number to use for exposing the REST service.
Note: This setting is ignored by the Servlet component, which uses the container's standard HTTP port instead. In the case of the Apache Karaf OSGi container, the standard HTTP port is normally 8181. It is good practice to set the port value nonetheless, for the sake of JMX and tooling.
|
contextPath() | @contextPath | Sets a leading context path for the REST services. This can be used with components such as Servlet, where the deployed Web application is deployed using a context-path setting. |
hostNameResolver() | @hostNameResolver |
If a hostname is not set explicitly, this resolver determines the host for the REST service. Possible values are
RestHostNameResolver.localHostName (Java DSL) or localHostName (XML DSL), which resolves to the host name format; and RestHostNameResolver.localIp (Java DSL) or localIp (XML DSL), which resolves to the dotted decimal IP address format. Default is localHostName .
|
bindingMode() | @bindingMode | Enables binding mode for JSON or XML format messages. Possible values are: off , auto , json , xml , or json_xml . Default is off . |
skipBindingOnErrorCode() | @skipBindingOnErrorCode |
Specifies whether to skip binding on output, if there is a custom HTTP error code header. This allows you to build custom error messages that do not bind to JSON or XML, as successful messages would otherwise do. Default is
true .
|
enableCORS() | @enableCORS | If true , enables CORS (cross-origin resource sharing) headers in the HTTP response. Default is false . |
jsonDataFormat() | @jsonDataFormat |
Specifies the component that Camel uses to implement the JSON data format. Possible values are:
json-jackson , json-gson , json-xstream . Default is json-jackson .
|
xmlDataFormat() | @xmlDataFormat |
Specifies the component that Camel uses to implement the XML data format. Possible value is:
jaxb . Default is jaxb .
|
componentProperty() | componentProperty | Enables you to set arbitrary component level properties on the underlying REST implementation. |
endpointProperty() | endpointProperty | Enables you to set arbitrary endpoint level properties on the underlying REST implementation. |
consumerProperty() | consumerProperty | Enables you to set arbitrary consumer endpoint properties on the underlying REST implementation. |
dataFormatProperty() | dataFormatProperty |
Enables you to set arbitrary properties on the underlying data format component (for example, Jackson or JAXB). From Camel 2.14.1 onwards, you can attach the following prefixes to the property keys:
To restrict the property setting to a specific format type (JSON or XML) and a particular message direction (IN or OUT).
|
corsHeaderProperty() | corsHeaders | Enables you to specify custom CORS headers, as key/value pairs. |
Default CORS headers
corsHeaderProperty
DSL command.
Header Key | Header Value |
---|---|
Access-Control-Allow-Origin | * |
Access-Control-Allow-Methods | GET , HEAD , POST , PUT , DELETE , TRACE , OPTIONS , CONNECT , PATCH
|
Access-Control-Allow-Headers | Origin , Accept , X-Requested-With , Content-Type , Access-Control-Request-Method , Access-Control-Request-Headers
|
Access-Control-Max-Age | 3600 |
Enabling or disabling Jackson JSON features
dataFormatProperty
option:
json.in.disableFeatures
json.in.enableFeatures
FAIL_ON_UNKNOWN_PROPERTIES
feature (which causes Jackson to fail if a JSON input has a property that cannot be mapped to a Java object):
restConfiguration().component("jetty") .host("localhost").port(getPort()) .bindingMode(RestBindingMode.json) .dataFormatProperty("json.in.disableFeatures", "FAIL_ON_UNKNOWN_PROPERTIES");
.dataFormatProperty("json.in.disableFeatures", "FAIL_ON_UNKNOWN_PROPERTIES,ADJUST_DATES_TO_CONTEXT_TIME_ZONE");
restConfiguration().component("jetty") .host("localhost").port(getPort()) .bindingMode(RestBindingMode.json) .dataFormatProperty("json.in.disableFeatures", "FAIL_ON_UNKNOWN_PROPERTIES,ADJUST_DATES_TO_CONTEXT_TIME_ZONE") .dataFormatProperty("json.in.enableFeatures", "FAIL_ON_NUMBERS_FOR_ENUMS,USE_BIG_DECIMAL_FOR_FLOATS");
<restConfiguration component="jetty" host="localhost" port="9090" bindingMode="json"> <dataFormatProperty key="json.in.disableFeatures" value="FAIL_ON_UNKNOWN_PROPERTIES,ADJUST_DATES_TO_CONTEXT_TIME_ZONE"/> <dataFormatProperty key="json.in.enableFeatures" value="FAIL_ON_NUMBERS_FOR_ENUMS,USE_BIG_DECIMAL_FOR_FLOATS"/> </restConfiguration>
enum
IDs from the following Jackson classes
4.5. Swagger Integration
Overview
camel-swagger
component enables users to create API docs for any REST-defined routes and endpoints in a CamelContext file. The camel-swagger
component creates a servlet integrated with the CamelContext that pulls the information from each REST endpoint to generate the API docs (JSON file).
camel-swagger
component to your pom.xml
file:
<dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-swagger</artifactId> <version>x.x.x</version> <!-- Use the same version as your Camel core version --> </dependency>
Configuring the camelContext
- The
service
element, which exposes the camel-swagger servlet and initializes its parameters.In the service element, add the servlet (org.apache.camel.component.swagger.DefaultCamelSwaggerServlet
) and theservice-properties
that configure the servlet's parameters.For details on servlet parameters, see chapter "Swagger" in "Apache Camel Component Reference". - Configure the REST implementationDefine the REST service within the
camelContext
element using therestConfiguration
andrest
elements.For details on configuring REST services in the CamelContext, see Section 4.2, “Defining Services with REST DSL”.
blueprint.xml
file; for example:
<?xml version="1.0" encoding="UTF-8"?> <blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.osgi.org/xmlns/blueprint/v1.0.0 http://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd http://camel.apache.org/schema/blueprint http://camel.apache.org/schema/blueprint/camel-blueprint.xsd"> <service interface="javax.servlet.http.HttpServlet"> <service-properties> <entry key="alias" value="/api-docs/*"/> <entry key="init-prefix" value="init."/> <entry key="init.base.path" value="//localhost:8080/"/> <entry key="init.api.path" value="//localhost:8181/api-docs"/> <entry key="init.api.title" value="Camel Rest Example API"/> <entry key="init.api.version" value="1.2"/> <entry key="init.api.description" value="Camel Rest Example with Swagger that provides an User REST service"/> </service-properties> <bean class="org.apache.camel.component.swagger.DefaultCamelSwaggerServlet" /> </service> <camelContext id="log-example-context" xmlns="http://camel.apache.org/schema/blueprint"> <restConfiguration component="jetty" port="8080"/> <rest path="/say"> <get uri="/hello"> <to uri="direct:hello"/> </get> <get uri="/bye" consumes="application/json"> <to uri="direct:bye"/> </get> <post uri="/bye"> <to uri="mock:update"/> </post> </rest> <route id="rte1-log-example"> <from uri="direct:hello"/> <transform> <constant>Hello World</constant> </transform> </route> <route id="rte2-log-example"> <from uri="direct:bye"/> <transform> <constant>Bye World</constant> </transform> </route> </camelContext> </blueprint>
-
service
- The
service
element exposes the camel swagger servlet (<bean class="org.apache.camel.component.swagger.DefaultCamelSwaggerServlet"/>
) and initializes several servlet properties. -
alias
- The
alias
property binds the camel swagger servlet to/api-docs/*
. -
init-prefix
- The
init-prefix
property sets the prefix for all camel swagger servlet properties toinit.
. This is analogous to usinginit-param
elements in theweb.xml
configuration for WAR implementations (see chapter "Swagger" in "Apache Camel Component Reference"). -
restConfiguration
- In the
camelContext
element, therestConfiguration
element specifies the REST implementation to use. In this case, it is Jetty web servlet on port 8080. -
rest
- In the
camelContext
element, therest
element defines a REST service and provides the base path (/say
) to it. In this case, the service consists of two REST endpoints,hello
andbye
, which are routed to their corresponding camel endpoints defined in theroute
elements.
Chapter 5. Messaging Systems
Abstract
5.1. Message
Overview
Figure 5.1. Message Pattern
Types of message
- In message — A message that travels through a route from a consumer endpoint to a producer endpoint (typically, initiating a message exchange).
- Out message — A message that travels through a route from a producer endpoint back to a consumer endpoint (usually, in response to an In message).
org.apache.camel.Message
interface.
Message structure
- Headers — Contains metadata or header data extracted from the message.
- Body — Usually contains the entire message in its original form.
- Attachments — Message attachments (required for integrating with certain messaging systems, such as JBI).
Correlating messages
Exchange objects
Accessing messages
header(String name)
,body()
— Returns the named header and the body of the current In message.outBody()
— Returns the body of the current Out message.
username
header, you can use the following Java DSL route:
from(SourceURL).setHeader("username", "John.Doe").to(TargetURL);
5.2. Message Channel
Overview
Figure 5.2. Message Channel Pattern
Message-oriented components
ActiveMQ
activemq:QueueName
activemq:topic:TopicName
Foo.Bar
, use the following endpoint URI:
activemq:Foo.Bar
JMS
jms:QueueName
jms:topic:TopicName
AMQP
amqp:QueueName
amqp:topic:TopicName
5.3. Message Endpoint
Overview
Figure 5.3. Message Endpoint Pattern
Types of endpoint
- Consumer endpoint — Appears at the start of a Apache Camel route and reads In messages from an incoming channel (equivalent to a receiver endpoint).
- Producer endpoint — Appears at the end of a Apache Camel route and writes In messages to an outgoing channel (equivalent to a sender endpoint). It is possible to define a route with multiple producer endpoints.
Endpoint URIs
- Endpoint URI for a consumer endpoint — Advertises a specific location (for example, to expose a service to which senders can connect). Alternatively, the URI can specify a message source, such as a message queue. The endpoint URI can include settings to configure the endpoint.
- Endpoint URI for a producer endpoint — Contains details of where to send messages and includes the settings to configure the endpoint. In some cases, the URI specifies the location of a remote receiver endpoint; in other cases, the destination can have an abstract form, such as a queue name.
ComponentPrefix:ComponentSpecificURI
Foo.Bar
, you can define an endpoint URI like the following:
jms:Foo.Bar
file://local/router/messages/foo
, directly to the producer endpoint, jms:Foo.Bar
, you can use the following Java DSL fragment:
from("file://local/router/messages/foo").to("jms:Foo.Bar");
<camelContext id="CamelContextID" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="file://local/router/messages/foo"/> <to uri="jms:Foo.Bar"/> </route> </camelContext>
5.4. Pipes and Filters
Overview
pipe
command). The advantage of the pipeline approach is that it enables you to compose services (some of which can be external to the Apache Camel application) to create more complex forms of message processing.
Figure 5.4. Pipes and Filters Pattern
Pipeline for the InOut exchange pattern
Figure 5.5. Pipeline for InOut Exchanges
from("jms:RawOrders").pipeline("cxf:bean:decrypt", "cxf:bean:authenticate", "cxf:bean:dedup", "jms:CleanOrders");
<camelContext id="buildPipeline" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="jms:RawOrders"/> <to uri="cxf:bean:decrypt"/> <to uri="cxf:bean:authenticate"/> <to uri="cxf:bean:dedup"/> <to uri="jms:CleanOrders"/> </route> </camelContext>
from
and to
elements is semantically equivalent to a pipeline. See the section called “Comparison of pipeline() and to() DSL commands”.
Pipeline for the InOnly and RobustInOnly exchange patterns
InOnly
and RobustInOnly
exchange patterns), a pipeline cannot be connected in the normal way. In this special case, the pipeline is constructed by passing a copy of the original In message to each of the endpoints in the pipeline, as shown in Figure 5.6, “Pipeline for InOnly Exchanges”. This type of pipeline is equivalent to a recipient list with fixed destinations(see Section 8.3, “Recipient List”).
Figure 5.6. Pipeline for InOnly Exchanges
Comparison of pipeline() and to() DSL commands
- Using the pipeline() processor command — Use the pipeline processor to construct a pipeline route as follows:
from(SourceURI).pipeline(FilterA, FilterB, TargetURI);
- Using the to() command — Use the
to()
command to construct a pipeline route as follows:from(SourceURI).to(FilterA, FilterB, TargetURI);
Alternatively, you can use the equivalent syntax:from(SourceURI).to(FilterA).to(FilterB).to(TargetURI);
to()
command syntax, because it is not always equivalent to a pipeline processor. In Java DSL, the meaning of to()
can be modified by the preceding command in the route. For example, when the multicast()
command precedes the to()
command, it binds the listed endpoints into a multicast pattern, instead of a pipeline pattern(see Section 8.11, “Multicast”).
5.5. Message Router
Overview
Figure 5.7. Message Router Pattern
choice()
processor, where each of the alternative target endpoints can be selected using a when()
subclause (for details of the choice processor, see Section 1.5, “Processors”).
Java DSL example
seda:a
, seda:b
, or seda:c
) depending on the contents of the foo
header:
from("seda:a").choice() .when(header("foo").isEqualTo("bar")).to("seda:b") .when(header("foo").isEqualTo("cheese")).to("seda:c") .otherwise().to("seda:d");
XML configuration example
<camelContext id="buildSimpleRouteWithChoice" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <choice> <when> <xpath>$foo = 'bar'</xpath> <to uri="seda:b"/> </when> <when> <xpath>$foo = 'cheese'</xpath> <to uri="seda:c"/> </when> <otherwise> <to uri="seda:d"/> </otherwise> </choice> </route> </camelContext>
Choice without otherwise
choice()
without an otherwise()
clause, any unmatched exchanges are dropped by default.
5.6. Message Translator
Overview
Figure 5.8. Message Translator Pattern
Bean integration
myMethodName()
, on the bean with ID, myTransformerBean
:
from("activemq:SomeQueue") .beanRef("myTransformerBean", "myMethodName") .to("mqseries:AnotherQueue");
myTransformerBean
bean is defined in either a Spring XML file or in JNDI. If, you omit the method name parameter from beanRef()
, the bean integration will try to deduce the method name to invoke by examining the message exchange.
Processor
instance to perform the transformation, as follows:
from("direct:start").process(new Processor() { public void process(Exchange exchange) { Message in = exchange.getIn(); in.setBody(in.getBody(String.class) + " World!"); } }).to("mock:result");
from("direct:start").setBody(body().append(" World!")).to("mock:result");
from("activemq:My.Queue"). to("velocity:com/acme/MyResponse.vm"). to("activemq:Another.Queue");
My.Queue
queue on ActiveMQ with a template generated response, then you could use a route like the following to send responses back to the JMSReplyTo
destination:
from("activemq:My.Queue"). to("velocity:com/acme/MyResponse.vm");
5.7. Message History
Overview
Limiting Character Length in Logs
[DEBUG ProducerCache - >>>> Endpoint[direct:start] Exchange[Message: 01234567890123456789... [Body clipped after 20 characters, total length is 1000]
- Customizing the Limit using Java DSL
- You can set the limit in Camel properties using Java DSL. For example,
context.getProperties().put(Exchange.LOG_DEBUG_BODY_MAX_CHARS, "500");
- Customizing the Limit using Spring DSL
- You can set the limit in Camel properties using Spring DSL. For example,
<camelContext> <properties> <property key="CamelLogDebugBodyMaxChars" value="500"/> </properties> </camelContext>
Chapter 6. Messaging Channels
Abstract
6.1. Point-to-Point Channel
Overview
Figure 6.1. Point to Point Channel Pattern
Components that support point-to-point channel
JMS
Foo.Bar
as follows:
jms:queue:Foo.Bar
queue:
, is optional, because the JMS component creates a queue endpoint by default. Therefore, you can also specify the following equivalent endpoint URI:
jms:Foo.Bar
ActiveMQ
Foo.Bar
as follows:
activemq:queue:Foo.Bar
SEDA
SedaQueue
as follows:
seda:SedaQueue
JPA
XMPP
6.2. Publish-Subscribe Channel
Overview
Figure 6.2. Publish Subscribe Channel Pattern
Components that support publish-subscribe channel
JMS
StockQuotes
as follows:
jms:topic:StockQuotes
ActiveMQ
StockQuotes
, as follows:
activemq:topic:StockQuotes
XMPP
Static subscription lists
Java DSL example
seda:a
, and three subscribers, seda:b
, seda:c
, and seda:d
:
from("seda:a").to("seda:b", "seda:c", "seda:d");
XML configuration example
<camelContext id="buildStaticRecipientList" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <to uri="seda:b"/> <to uri="seda:c"/> <to uri="seda:d"/> </route> </camelContext>
6.3. Dead Letter Channel
Overview
Figure 6.3. Dead Letter Channel Pattern
Creating a dead letter channel in Java DSL
errorHandler(deadLetterChannel("seda:errors")); from("seda:a").to("seda:b");
errorHandler()
method is a Java DSL interceptor, which implies that all of the routes defined in the current route builder are affected by this setting. The deadLetterChannel()
method is a Java DSL command that creates a new dead letter channel with the specified destination endpoint, seda:errors
.
errorHandler()
interceptor provides a catch-all mechanism for handling all error types. If you want to apply a more fine-grained approach to exception handling, you can use the onException
clauses instead(see the section called “onException clause”).
XML DSL example
<route errorHandlerRef="myDeadLetterErrorHandler"> ... </route> <bean id="myDeadLetterErrorHandler" class="org.apache.camel.builder.DeadLetterChannelBuilder"> <property name="deadLetterUri" value="jms:queue:dead"/> <property name="redeliveryPolicy" ref="myRedeliveryPolicyConfig"/> </bean> <bean id="myRedeliveryPolicyConfig" class="org.apache.camel.processor.RedeliveryPolicy"> <property name="maximumRedeliveries" value="3"/> <property name="redeliveryDelay" value="5000"/> </bean>
Redelivery policy
errorHandler(deadLetterChannel("seda:errors").maximumRedeliveries(2).useExponentialBackOff()); from("seda:a").to("seda:b");
RedeliveryPolicy
object). Table 6.1, “Redelivery Policy Settings” summarizes the methods that you can use to set redelivery policies.
Method Signature | Default | Description |
---|---|---|
allowRedeliveryWhileStopping() | true | Controls whether redelivery is attempted during graceful shutdown or while a route is stopping. A delivery that is already in progress when stopping is initiated will not be interrupted. |
backOffMultiplier(double multiplier) | 2 |
If exponential backoff is enabled, let
m be the backoff multiplier and let d be the initial delay. The sequence of redelivery attempts are then timed as follows:
d, m*d, m*m*d, m*m*m*d, ... |
collisionAvoidancePercent(double collisionAvoidancePercent) | 15 | If collision avoidance is enabled, let p be the collision avoidance percent. The collision avoidance policy then tweaks the next delay by a random amount, up to plus/minus p% of its current value. |
deadLetterHandleNewException | true | Camel 2.15: Specifies whether or not to handle an exception that occurs while processing a message in the dead letter channel. If true , the exception is handled and a logged at the WARN level (so that the dead letter channel is guaranteed to complete). If false , the exception is not handled, so the dead letter channel fails, and propagates the new exception. |
delayPattern(String delayPattern) | None | Apache Camel 2.0: |
disableRedelivery() | true | Apache Camel 2.0: Disables the redelivery feature. To enable redelivery, set maximumRedeliveries() to a positive integer value. |
handled(boolean handled) | true | Apache Camel 2.0: If true , the current exception is cleared when the message is moved to the dead letter channel; if false , the exception is propagated back to the client. |
initialRedeliveryDelay(long initialRedeliveryDelay) | 1000 | Specifies the delay (in milliseconds) before attempting the first redelivery. |
logNewException | true | Specifies whether to log at WARN level, when an exception is raised in the dead letter channel. |
logStackTrace(boolean logStackTrace) | false | Apache Camel 2.0: If true , the JVM stack trace is included in the error logs. |
maximumRedeliveries(int maximumRedeliveries) | 0 | Apache Camel 2.0: Maximum number of delivery attempts. |
maximumRedeliveryDelay(long maxDelay) | 60000 | Apache Camel 2.0: When using an exponential backoff strategy (see useExponentialBackOff() ), it is theoretically possible for the redelivery delay to increase without limit. This property imposes an upper limit on the redelivery delay (in milliseconds) |
onRedelivery(Processor processor) | None | Apache Camel 2.0: Configures a processor that gets called before every redelivery attempt. |
redeliveryDelay(long int) | 0 | Apache Camel 2.0: Specifies the delay (in milliseconds) between redelivery attempts. |
retriesExhaustedLogLevel(LoggingLevel logLevel) | LoggingLevel.ERROR | Apache Camel 2.0: Specifies the logging level at which to log delivery failure (specified as an org.apache.camel.LoggingLevel constant). |
retryAttemptedLogLevel(LoggingLevel logLevel) | LoggingLevel.DEBUG | Apache Camel 2.0: Specifies the logging level at which to redelivery attempts (specified as an org.apache.camel.LoggingLevel constant). |
useCollisionAvoidance() | false | Enables collision avoidence, which adds some randomization to the backoff timings to reduce contention probability. |
useOriginalMessage() | false | Apache Camel 2.0: If this feature is enabled, the message sent to the dead letter channel is a copy of the original message exchange, as it existed at the beginning of the route (in the from() node). |
useExponentialBackOff() | false | Enables exponential backoff. |
Redelivery headers
Header Name | Type | Description |
---|---|---|
CamelRedeliveryCounter | Integer | Apache Camel 2.0: Counts the number of unsuccessful delivery attempts. This value is also set in Exchange.REDELIVERY_COUNTER . |
CamelRedelivered | Boolean | Apache Camel 2.0: True, if one or more redelivery attempts have been made. This value is also set in Exchange.REDELIVERED . |
CamelRedeliveryMaxCounter | Integer | Apache Camel 2.6: Holds the maximum redelivery setting (also set in the Exchange.REDELIVERY_MAX_COUNTER exchange property). This header is absent if you use retryWhile or have unlimited maximum redelivery configured. |
Redelivery exchange properties
Exchange Property Name | Type | Description |
---|---|---|
Exchange.FAILURE_ROUTE_ID | String | Provides the route ID of the route that failed. The literal name of this property is CamelFailureRouteId . |
Using the original message
from("jms:queue:order:input") .to("bean:validateOrder"); .to("bean:transformOrder") .to("bean:handleOrder");
validateOrder
, transformOrder
, and handleOrder
. But when an error occurs, we do not know in which state the message is in. Did the error happen before the transformOrder
bean or after? We can ensure that the original message from jms:queue:order:input
is logged to the dead letter channel by enabling the useOriginalMessage
option as follows:
// will use original body errorHandler(deadLetterChannel("jms:queue:dead") .useOriginalMessage().maximumRedeliveries(5).redeliveryDelay(5000);
Redeliver delay pattern
delayPattern
option is used to specify delays for particular ranges of the redelivery count. The delay pattern has the following syntax: limit1:delay1;limit2:delay2;limit3:delay3;...
, where each delayN is applied to redeliveries in the range limitN <= redeliveryCount < limitN+1
5:1000;10:5000;20:20000
, which defines three groups and results in the following redelivery delays:
- Attempt number 1..4 = 0 milliseconds (as the first group starts with 5).
- Attempt number 5..9 = 1000 milliseconds (the first group).
- Attempt number 10..19 = 5000 milliseconds (the second group).
- Attempt number 20.. = 20000 milliseconds (the last group).
1:1000;5:5000
results in the following redelivery delays:
- Attempt number 1..4 = 1000 millis (the first group)
- Attempt number 5.. = 5000 millis (the last group)
1:5000;3:1000
, starts with a 5 second delay and then reduces the delay to 1 second.
Which endpoint failed?
// Java String lastEndpointUri = exchange.getProperty(Exchange.TO_ENDPOINT, String.class);
Exchange.TO_ENDPOINT
is a string constant equal to CamelToEndpoint
. This property is updated whenever Camel sends a message to any endpoint.
CamelFailureEndpoint
, which identifies the last destination the exchange was sent to before the error occcured. Hence, you can access the failure endpoint from within a dead letter queue using the following code:
// Java String failedEndpointUri = exchange.getProperty(Exchange.FAILURE_ENDPOINT, String.class);
Exchange.FAILURE_ENDPOINT
is a string constant equal to CamelFailureEndpoint
.
from("activemq:queue:foo") .to("http://someserver/somepath") .beanRef("foo");
foo
bean. In this case the Exchange.TO_ENDPOINT
property and the Exchange.FAILURE_ENDPOINT
property still contain the value.
onRedelivery processor
Processor
that is executed just before every redelivery attempt. This can be used for situations where you need to alter the message before it is redelivered.
MyRedeliverProcessor
before redelivering exchanges:
// we configure our Dead Letter Channel to invoke // MyRedeliveryProcessor before a redelivery is // attempted. This allows us to alter the message before errorHandler(deadLetterChannel("mock:error").maximumRedeliveries(5) .onRedelivery(new MyRedeliverProcessor()) // setting delay to zero is just to make unit teting faster .redeliveryDelay(0L));
MyRedeliveryProcessor
process is implemented as follows:
// This is our processor that is executed before every redelivery attempt
// here we can do what we want in the java code, such as altering the message
public class MyRedeliverProcessor implements Processor {
public void process(Exchange exchange) throws Exception {
// the message is being redelivered so we can alter it
// we just append the redelivery counter to the body
// you can of course do all kind of stuff instead
String body = exchange.getIn().getBody(String.class);
int count = exchange.getIn().getHeader(Exchange.REDELIVERY_COUNTER, Integer.class);
exchange.getIn().setBody(body + count);
// the maximum redelivery was set to 5
int max = exchange.getIn().getHeader(Exchange.REDELIVERY_MAX_COUNTER, Integer.class);
assertEquals(5, max);
}
}
Control redelivery during shutdown or stopping
allowRedeliveryWhileStopping
option to false
, as shown in the following example:
errorHandler(deadLetterChannel("jms:queue:dead")
.allowRedeliveryWhileStopping(false)
.maximumRedeliveries(20)
.redeliveryDelay(1000)
.retryAttemptedLogLevel(LoggingLevel.INFO));
allowRedeliveryWhileStopping
option is true
by default, for backwards compatibility reasons. During aggressive shutdown, however, redelivery is always suppressed, irrespective of this option setting (for example, after graceful shutdown has timed out).
onException clause
errorHandler()
interceptor in your route builder, you can define a series of onException()
clauses that define different redelivery policies and different dead letter channels for various exception types. For example, to define distinct behavior for each of the NullPointerException
, IOException
, and Exception
types, you can define the following rules in your route builder using Java DSL:
onException(NullPointerException.class) .maximumRedeliveries(1) .setHeader("messageInfo", "Oh dear! An NPE.") .to("mock:npe_error"); onException(IOException.class) .initialRedeliveryDelay(5000L) .maximumRedeliveries(3) .backOffMultiplier(1.0) .useExponentialBackOff() .setHeader("messageInfo", "Oh dear! Some kind of I/O exception.") .to("mock:io_error"); onException(Exception.class) .initialRedeliveryDelay(1000L) .maximumRedeliveries(2) .setHeader("messageInfo", "Oh dear! An exception.") .to("mock:error"); from("seda:a").to("seda:b");
to()
DSL command. You can also call other Java DSL commands in the onException()
clauses. For example, the preceding example calls setHeader()
to record some error details in a message header named, messageInfo
.
NullPointerException
and the IOException
exception types are configured specially. All other exception types are handled by the generic Exception
exception interceptor. By default, Apache Camel applies the exception interceptor that most closely matches the thrown exception. If it fails to find an exact match, it tries to match the closest base type, and so on. Finally, if no other interceptor matches, the interceptor for the Exception
type matches all remaining exceptions.
6.4. Guaranteed Delivery
Overview
Figure 6.4. Guaranteed Delivery Pattern
Components that support guaranteed delivery
JMS
deliveryPersistent
query option indicates whether or not persistent storage of messages is enabled. Usually it is unnecessary to set this option, because the default behavior is to enable persistent delivery. To configure all the details of guaranteed delivery, it is necessary to set configuration options on the JMS provider. These details vary, depending on what JMS provider you are using. For example, MQSeries, TibCo, BEA, Sonic, and others, all provide various qualities of service to support guaranteed delivery.
ActiveMQ
META-INF/spring/camel-context.xml
, you can configure the ActiveMQ component to connect to the central broker using the OpenWire/TCP protocol as follows:
<beans ... > ... <bean id="activemq" class="org.apache.activemq.camel.component.ActiveMQComponent"> <property name="brokerURL" value="tcp://somehost:61616"/> </bean> ... </beans>
camel-context.xml
configuration file, you can configure the ActiveMQ component to connect to all of the peers in group, GroupA
, as follows:
<beans ... > ... <bean id="activemq" class="org.apache.activemq.camel.component.ActiveMQComponent"> <property name="brokerURL" value="peer://GroupA/broker1"/> </bean> ... </beans>
broker1
is the broker name of the embedded broker (other peers in the group should use different broker names). One limiting feature of the Peer-to-Peer protocol is that it relies on IP multicast to locate the other peers in its group. This makes it unsuitable for use in wide area networks (and in some local area networks that do not have IP multicast enabled).
<beans ... > ... <bean id="activemq" class="org.apache.activemq.camel.component.ActiveMQComponent"> <property name="brokerURL" value="vm://broker1?brokerConfig=xbean:activemq.xml"/> </bean> ... </beans>
activemq.xml
is an ActiveMQ file which configures the embedded broker instance. Within the ActiveMQ configuration file, you can choose to enable one of the following persistence mechanisms:
- AMQ persistence(the default) — A fast and reliable message store that is native to ActiveMQ. For details, see amqPersistenceAdapter and AMQ Message Store.
- JDBC persistence — Uses JDBC to store messages in any JDBC-compatible database. For details, see jdbcPersistenceAdapter and ActiveMQ Persistence.
- Journal persistence — A fast persistence mechanism that stores messages in a rolling log file. For details, see journalPersistenceAdapter and ActiveMQ Persistence.
- Kaha persistence — A persistence mechanism developed specifically for ActiveMQ. For details, see kahaPersistenceAdapter and ActiveMQ Persistence.
ActiveMQ Journal
6.5. Message Bus
Overview
Figure 6.5. Message Bus Pattern
- Common communication infrastructure — The router itself provides the core of the common communication infrastructure in Apache Camel. However, in contrast to some message bus architectures, Apache Camel provides a heterogeneous infrastructure: messages can be sent into the bus using a wide variety of different transports and using a wide variety of different message formats.
- Adapters — Where necessary, Apache Camel can translate message formats and propagate messages using different transports. In effect, Apache Camel is capable of behaving like an adapter, so that external applications can hook into the message bus without refactoring their messaging protocols.In some cases, it is also possible to integrate an adapter directly into an external application. For example, if you develop an application using Apache CXF, where the service is implemented using JAX-WS and JAXB mappings, it is possible to bind a variety of different transports to the service. These transport bindings function as adapters.
Chapter 7. Message Construction
Abstract
7.1. Correlation Identifier
Overview
JMSCorrelationID
. You can add your own correlation identifier to any message exchange to help correlate messages together in a single conversation (or business process). A correlation identifier is usually stored in a Apache Camel message header.
Exchange.CORRELATION_ID
, which links back to the source Exchanges. For example, the Splitter, Multicast, Recipient List, and Wire Tap EIPs do this.
Figure 7.1. Correlation Identifier Pattern
7.2. Event Message
Event Message
Explicitly specifying InOnly
foo:bar?exchangePattern=InOnly
from("mq:someQueue"). inOnly(). bean(Foo.class);
from("mq:someQueue"). inOnly("mq:anotherQueue");
<route> <from uri="mq:someQueue"/> <inOnly uri="bean:foo"/> </route>
<route> <from uri="mq:someQueue"/> <inOnly uri="mq:anotherQueue"/> </route>
7.3. Return Address
Return Address
JMSReplyTo
header.
JMSReplyTo
.
Example
getMockEndpoint("mock:bar").expectedBodiesReceived("Bye World"); template.sendBodyAndHeader("direct:start", "World", "JMSReplyTo", "queue:bar");
from("direct:start").to("activemq:queue:foo?preserveMessageQos=true"); from("activemq:queue:foo").transform(body().prepend("Bye ")); from("activemq:queue:bar?disableReplyTo=true").to("mock:bar");
<route> <from uri="direct:start"/> <to uri="activemq:queue:foo?preserveMessageQos=true"/> </route> <route> <from uri="activemq:queue:foo"/> <transform> <simple>Bye ${in.body}</simple> </transform> </route> <route> <from uri="activemq:queue:bar?disableReplyTo=true"/> <to uri="mock:bar"/> </route>
Chapter 8. Message Routing
Abstract
8.1. Content-Based Router
Overview
Figure 8.1. Content-Based Router Pattern
Java DSL example
seda:a
, endpoint to either seda:b
, queue:c
, or seda:d
depending on the evaluation of various predicate expressions:
RouteBuilder builder = new RouteBuilder() { public void configure() { from("seda:a").choice() .when(header("foo").isEqualTo("bar")).to("seda:b") .when(header("foo").isEqualTo("cheese")).to("seda:c") .otherwise().to("seda:d"); } };
XML configuration example
<camelContext id="buildSimpleRouteWithChoice" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <choice> <when> <xpath>$foo = 'bar'</xpath> <to uri="seda:b"/> </when> <when> <xpath>$foo = 'cheese'</xpath> <to uri="seda:c"/> </when> <otherwise> <to uri="seda:d"/> </otherwise> </choice> </route> </camelContext>
8.2. Message Filter
Overview
filter()
Java DSL command. The filter()
command takes a single predicate argument, which controls the filter. When the predicate is true
, the incoming message is allowed to proceed, and when the predicate is false
, the incoming message is blocked.
Figure 8.2. Message Filter Pattern
Java DSL example
seda:a
, to endpoint, seda:b
, that blocks all messages except for those messages whose foo
header have the value, bar
:
RouteBuilder builder = new RouteBuilder() { public void configure() { from("seda:a").filter(header("foo").isEqualTo("bar")).to("seda:b"); } };
person
element whose name
attribute is equal to James
:
from("direct:start"). filter().xpath("/person[@name='James']"). to("mock:result");
XML configuration example
<camelContext id="simpleFilterRoute" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <filter> <xpath>$foo = 'bar'</xpath> <to uri="seda:b"/> </filter> </route> </camelContext>
<to uri="seda:b"/>
) before the closing </filter>
tag or the filter will not be applied (in 2.8+, omitting this will result in an error).
Filtering with beans
from("direct:start") .filter().method(MyBean.class, "isGoldCustomer").to("mock:result").end() .to("mock:end"); public static class MyBean { public boolean isGoldCustomer(@Header("level") String level) { return level.equals("gold"); } }
Using stop()
Bye
in the message body to propagate any further in the route. We prevent this in the when()
predicate using .stop()
.
from("direct:start")
.choice()
.when(bodyAs(String.class).contains("Hello")).to("mock:hello")
.when(bodyAs(String.class).contains("Bye")).to("mock:bye").stop()
.otherwise().to("mock:other")
.end()
.to("mock:result");
Knowing if Exchange was filtered or not
Exchannge.FILTER_MATCHED
which has the String value of CamelFilterMatched
. Its value is a boolean indicating true
or false
. If the value is true
then the Exchange was routed in the filter block.
8.3. Recipient List
Overview
Figure 8.3. Recipient List Pattern
Recipient list with fixed destinations
to()
Java DSL command.
Java DSL example
queue:a
, to a fixed list of destinations:
from("seda:a").to("seda:b", "seda:c", "seda:d");
XML configuration example
<camelContext id="buildStaticRecipientList" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <to uri="seda:b"/> <to uri="seda:c"/> <to uri="seda:d"/> </route> </camelContext>
Recipient list calculated at run time
recipientList()
processor, which takes a list of destinations as its sole argument. Because Apache Camel applies a type converter to the list argument, it should be possible to use most standard Java list types (for example, a collection, a list, or an array). For more details about type converters, see Section 42.3, “Built-In Type Converters”.
Java DSL example
recipientListHeader
, where the header value is a comma-separated list of endpoint URIs:
from("direct:a").recipientList(header("recipientListHeader").tokenize(","));
recipientList()
. For example:
from("seda:a").recipientList(header("recipientListHeader"));
XML configuration example
<camelContext id="buildDynamicRecipientList" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <recipientList delimiter=","> <header>recipientListHeader</header> </recipientList> </route> </camelContext>
Sending to multiple recipients in parallel
parallelProcessing
, which is similar to the corresponding feature in Splitter. Use the parallel processing feature to send the exchange to multiple recipients concurrently—for example:
from("direct:a").recipientList(header("myHeader")).parallelProcessing();
recipientList
tag—for example:
<route> <from uri="direct:a"/> <recipientList parallelProcessing="true"> <header>myHeader</header> </recipientList> </route>
Stop on exception
stopOnException
feature, which you can use to stop sending to any further recipients, if any recipient fails.
from("direct:a").recipientList(header("myHeader")).stopOnException();
recipientList
tag—for example:
<route> <from uri="direct:a"/> <recipientList stopOnException="true"> <header>myHeader</header> </recipientList> </route>
parallelProcessing
and stopOnException
in the same route.
Ignore invalid endpoints
ignoreInvalidEndpoints
option, which enables the recipient list to skip invalid endpoints (Routing Slip also supports this option). For example:
from("direct:a").recipientList(header("myHeader")).ignoreInvalidEndpoints();
ignoreInvalidEndpoints
attribute on the recipientList
tag, as follows
<route> <from uri="direct:a"/> <recipientList ignoreInvalidEndpoints="true"> <header>myHeader</header> </recipientList> </route>
myHeader
contains the two endpoints, direct:foo,xxx:bar
. The first endpoint is valid and works. The second is invalid and, therefore, ignored. Apache Camel logs at INFO
level whenever an invalid endpoint is encountered.
Using custom AggregationStrategy
AggregationStrategy
with the Recipient List, which is useful for aggregating replies from the recipients in the list. By default, Apache Camel uses the UseLatestAggregationStrategy
aggregation strategy, which keeps just the last received reply. For a more sophisticated aggregation strategy, you can define your own implementation of the AggregationStrategy
interface—see Aggregator EIP for details. For example, to apply the custom aggregation strategy, MyOwnAggregationStrategy
, to the reply messages, you can define a Java DSL route as follows:
from("direct:a") .recipientList(header("myHeader")).aggregationStrategy(new MyOwnAggregationStrategy()) .to("direct:b");
recipientList
tag, as follows:
<route> <from uri="direct:a"/> <recipientList strategyRef="myStrategy"> <header>myHeader</header> </recipientList> <to uri="direct:b"/> </route> <bean id="myStrategy" class="com.mycompany.MyOwnAggregationStrategy"/>
Using custom thread pool
parallelProcessing
. By default Camel uses a thread pool with 10 threads. Notice this is subject to change when we overhaul thread pool management and configuration later (hopefully in Camel 2.2).
Using method call as recipient list
from("activemq:queue:test").recipientList().method(MessageRouter.class, "routeTo");
MessageRouter
bean is defined as follows:
public class MessageRouter { public String routeTo() { String queueName = "activemq:queue:test2"; return queueName; } }
Bean as recipient list
@RecipientList
annotation to a methods that returns a list of recipients. For example:
public class MessageRouter { @RecipientList public String routeTo() { String queueList = "activemq:queue:test1,activemq:queue:test2"; return queueList; } }
recipientList
DSL command in the route. Define the route as follows:
from("activemq:queue:test").bean(MessageRouter.class, "routeTo");
Using timeout
parallelProcessing
, you can configure a total timeout
value in milliseconds. Camel will then process the messages in parallel until the timeout is hit. This allows you to continue processing if one message is slow.
recipientlist
header has the value, direct:a,direct:b,direct:c
, so that the message is sent to three recipients. We have a timeout of 250 milliseconds, which means only the last two messages can be completed within the timeframe. The aggregation therefore yields the string result, BC
.
from("direct:start") .recipientList(header("recipients"), ",") .aggregationStrategy(new AggregationStrategy() { public Exchange aggregate(Exchange oldExchange, Exchange newExchange) { if (oldExchange == null) { return newExchange; } String body = oldExchange.getIn().getBody(String.class); oldExchange.getIn().setBody(body + newExchange.getIn().getBody(String.class)); return oldExchange; } }) .parallelProcessing().timeout(250) // use end to indicate end of recipientList clause .end() .to("mock:result"); from("direct:a").delay(500).to("mock:A").setBody(constant("A")); from("direct:b").to("mock:B").setBody(constant("B")); from("direct:c").to("mock:C").setBody(constant("C"));
timeout
feature is also supported by splitter
and both multicast
and recipientList
.
AggregationStrategy
is not invoked. However you can implement a specialized version
// Java public interface TimeoutAwareAggregationStrategy extends AggregationStrategy { /** * A timeout occurred * * @param oldExchange the oldest exchange (is <tt>null</tt> on first aggregation as we only have the new exchange) * @param index the index * @param total the total * @param timeout the timeout value in millis */ void timeout(Exchange oldExchange, int index, int total, long timeout);
AggregationStrategy
if you really need to.
timeout
method in the TimeoutAwareAggregationStrategy
once, for the first index which caused the timeout.
Apply custom processing to the outgoing messages
recipientList
sends a message to one of the recipient endpoints, it creates a message replica, which is a shallow copy of the original message. If you want to perform some custom processing on each message replica before the replica is sent to its endpoint, you can invoke the onPrepare
DSL command in the recipientList
clause. The onPrepare
command inserts a custom processor just after the message has been shallow-copied and just before the message is dispatched to its endpoint. For example, in the following route, the CustomProc
processor is invoked on the message replica for each recipient endpoint:
from("direct:start") .recipientList().onPrepare(new CustomProc());
onPrepare
DSL command is to perform a deep copy of some or all elements of a message. This allows each message replica to be modified independently of the others. For example, the following CustomProc
processor class performs a deep copy of the message body, where the message body is presumed to be of type, BodyType
, and the deep copy is performed by the method, BodyType.deepCopy()
.
// Java import org.apache.camel.*; ... public class CustomProc implements Processor { public void process(Exchange exchange) throws Exception { BodyType body = exchange.getIn().getBody(BodyType.class); // Make a _deep_ copy of of the body object BodyType clone = BodyType.deepCopy(); exchange.getIn().setBody(clone); // Headers and attachments have already been // shallow-copied. If you need deep copies, // add some more code here. } }
Options
recipientList
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
delimiter
|
,
|
Delimiter used if the Expression returned multiple endpoints. |
strategyRef
|
Refers to an AggregationStrategy to be used to assemble the replies from the recipients, into a single outgoing message from the Recipient List. By default Camel will use the last reply as the outgoing message. | |
strategyMethodName
|
This option can be used to explicitly specify the method name to use, when using POJOs as the AggregationStrategy .
|
|
strategyMethodAllowNull
|
false
|
This option can be used, when using POJOs as the AggregationStrategy . If false , the aggregate method is not used, when there is no data to enrich. If true , null values are used for the oldExchange , when there is no data to enrich.
|
parallelProcessing
|
false
|
Camel 2.2: If enables then sending messages to the recipients occurs concurrently. Note the caller thread will still wait until all messages has been fully processed, before it continues. Its only the sending and processing the replies from the recipients which happens concurrently. |
parallelAggregate
|
false
|
If enabled, the aggregate method on AggregationStrategy can be called concurrently. Note that this requires the implementation of AggregationStrategy to be thread-safe. By default, this option is false , which means that Camel automatically synchronizes calls to the aggregate method. In some use-cases, however, you can improve performance by implementing AggregationStrategy as thread-safe and setting this option to true .
|
executorServiceRef
|
Camel 2.2: Refers to a custom Thread Pool to be used for parallel processing. Notice if you set this option, then parallel processing is automatic implied, and you do not have to enable that option as well. | |
stopOnException
|
false
|
Camel 2.2: Whether or not to stop continue processing immediately when an exception occurred. If disable, then Camel will send the message to all recipients regardless if one of them failed. You can deal with exceptions in the AggregationStrategy class where you have full control how to handle that. |
ignoreInvalidEndpoints
|
false
|
Camel 2.3: If an endpoint uri could not be resolved, should it be ignored. Otherwise Camel will thrown an exception stating the endpoint uri is not valid. |
streaming
|
false
|
Camel 2.5: If enabled then Camel will process replies out-of-order, eg in the order they come back. If disabled, Camel will process replies in the same order as the Expression specified. |
timeout
|
Camel 2.5: Sets a total timeout specified in millis. If the Recipient List hasn't been able to send and process all replies within the given timeframe, then the timeout triggers and the Recipient List breaks out and continues. Notice if you provide a TimeoutAwareAggregationStrategy then the timeout method is invoked before breaking out.
|
|
onPrepareRef
|
Camel 2.8: Refers to a custom Processor to prepare the copy of the Exchange each recipient will receive. This allows you to do any custom logic, such as deep-cloning the message payload if that's needed etc. | |
shareUnitOfWork
|
false
|
Camel 2.8: Whether the unit of work should be shared. See the same option on Splitter for more details. |
cacheSize
|
0
|
Camel 2.13.1/2.12.4: Allows to configure the cache size for the ProducerCache which caches producers for reuse in the routing slip. Will by default use the default cache size which is 0. Setting the value to -1 allows to turn off the cache all together. |
Using Exchange Pattern in Recipient List
from("file:inbox") // the exchange pattern is InOnly initially when using a file route .recipientList().constant("activemq:queue:inbox?exchangePattern=InOut") .to("file:outbox");
InOut
exchange pattern must get a response during the timeout. However, it fails if the response is not recieved.
8.4. Splitter
Overview
split()
Java DSL command.
Figure 8.4. Splitter Pattern
- Simple splitter—implements the splitter pattern on its own.
- Splitter/aggregator—combines the splitter pattern with the aggregator pattern, such that the pieces of the message are recombined after they have been processed.
Java DSL example
seda:a
to seda:b
that splits messages by converting each line of an incoming message into a separate outgoing message:
RouteBuilder builder = new RouteBuilder() { public void configure() { from("seda:a") .split(bodyAs(String.class).tokenize("\n")) .to("seda:b"); } };
bar
elements from an incoming message and insert them into separate outgoing messages:
from("activemq:my.queue") .split(xpath("//foo/bar")) .to("file://some/directory")
XML configuration example
<camelContext id="buildSplitter" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <split> <xpath>//foo/bar</xpath> <to uri="seda:b"/> </split> </route> </camelContext>
tokenize
element. In the following example, the message body is tokenized using the \n
separator character. To use a regular expression pattern, set regex=true
in the tokenize
element.
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <split> <tokenize token="\n"/> <to uri="mock:result"/> </split> </route> </camelContext>
Splitting into groups of lines
from("file:inbox") .split().tokenize("\n", 1000).streaming() .to("activemq:queue:order");
tokenize
specifies the number of lines that should be grouped into a single chunk. The streaming()
clause directs the splitter not to read the whole file at once (resulting in much better performance if the file is large).
<route> <from uri="file:inbox"/> <split streaming="true"> <tokenize token="\n" group="1000"/> <to uri="activemq:queue:order"/> </split> </route>
group
option is always of java.lang.String
type.
Splitter reply
Parallel execution
XPathBuilder xPathBuilder = new XPathBuilder("//foo/bar"); from("activemq:my.queue").split(xPathBuilder).parallelProcessing().to("activemq:my.parts");
ThreadPoolExecutor
used in the parallel splitter. For example, you can specify a custom executor in the Java DSL as follows:
XPathBuilder xPathBuilder = new XPathBuilder("//foo/bar"); ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(8, 16, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue()); from("activemq:my.queue") .split(xPathBuilder) .parallelProcessing() .executorService(threadPoolExecutor) .to("activemq:my.parts");
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:parallel-custom-pool"/> <split executorServiceRef="threadPoolExecutor"> <xpath>/invoice/lineItems</xpath> <to uri="mock:result"/> </split> </route> </camelContext> <bean id="threadPoolExecutor" class="java.util.concurrent.ThreadPoolExecutor"> <constructor-arg index="0" value="8"/> <constructor-arg index="1" value="16"/> <constructor-arg index="2" value="0"/> <constructor-arg index="3" value="MILLISECONDS"/> <constructor-arg index="4"><bean class="java.util.concurrent.LinkedBlockingQueue"/></constructor-arg> </bean>
Using a bean to perform splitting
method()
expression. The bean should return an iterable value such as: java.util.Collection
, java.util.Iterator
, or an array.
method()
expression that calls a method on the mySplitterBean
bean instance:
from("direct:body") // here we use a POJO bean mySplitterBean to do the split of the payload .split() .method("mySplitterBean", "splitBody") .to("mock:result"); from("direct:message") // here we use a POJO bean mySplitterBean to do the split of the message // with a certain header value .split() .method("mySplitterBean", "splitMessage") .to("mock:result");
mySplitterBean
is an instance of the MySplitterBean
class, which is defined as follows:
public class MySplitterBean { /** * The split body method returns something that is iteratable such as a java.util.List. * * @param body the payload of the incoming message * @return a list containing each part split */ public List<String> splitBody(String body) { // since this is based on an unit test you can of couse // use different logic for splitting as Apache Camel have out // of the box support for splitting a String based on comma // but this is for show and tell, since this is java code // you have the full power how you like to split your messages List<String> answer = new ArrayList<String>(); String[] parts = body.split(","); for (String part : parts) { answer.add(part); } return answer; } /** * The split message method returns something that is iteratable such as a java.util.List. * * @param header the header of the incoming message with the name user * @param body the payload of the incoming message * @return a list containing each part split */ public List<Message> splitMessage(@Header(value = "user") String header, @Body String body) { // we can leverage the Parameter Binding Annotations // http://camel.apache.org/parameter-binding-annotations.html // to access the message header and body at same time, // then create the message that we want, splitter will // take care rest of them. // *NOTE* this feature requires Apache Camel version >= 1.6.1 List<Message> answer = new ArrayList<Message>(); String[] parts = header.split(","); for (String part : parts) { DefaultMessage message = new DefaultMessage(); message.setHeader("user", part); message.setBody(body); answer.add(message); } return answer; } }
Exchange properties
header | type | description |
---|---|---|
CamelSplitIndex
|
int
|
Apache Camel 2.0: A split counter that increases for each Exchange being split. The counter starts from 0. |
CamelSplitSize
|
int
|
Apache Camel 2.0: The total number of Exchanges that was split. This header is not applied for stream based splitting. |
CamelSplitComplete
|
boolean
|
Apache Camel 2.4: Whether or not this Exchange is the last. |
Splitter/aggregator pattern
split()
DSL command lets you provide an AggregationStrategy
object as the second argument.
Java DSL example
from("direct:start") .split(body().tokenize("@"), new MyOrderStrategy()) // each split message is then send to this bean where we can process it .to("bean:MyOrderService?method=handleOrder") // this is important to end the splitter route as we do not want to do more routing // on each split message .end() // after we have split and handled each message we want to send a single combined // response back to the original caller, so we let this bean build it for us // this bean will receive the result of the aggregate strategy: MyOrderStrategy .to("bean:MyOrderService?method=buildCombinedResponse")
AggregationStrategy implementation
MyOrderStrategy
, used in the preceding route is implemented as follows:
/** * This is our own order aggregation strategy where we can control * how each split message should be combined. As we do not want to * lose any message, we copy from the new to the old to preserve the * order lines as long we process them */ public static class MyOrderStrategy implements AggregationStrategy { public Exchange aggregate(Exchange oldExchange, Exchange newExchange) { // put order together in old exchange by adding the order from new exchange if (oldExchange == null) { // the first time we aggregate we only have the new exchange, // so we just return it return newExchange; } String orders = oldExchange.getIn().getBody(String.class); String newLine = newExchange.getIn().getBody(String.class); LOG.debug("Aggregate old orders: " + orders); LOG.debug("Aggregate new order: " + newLine); // put orders together separating by semi colon orders = orders + ";" + newLine; // put combined order back on old to preserve it oldExchange.getIn().setBody(orders); // return old as this is the one that has all the orders gathered until now return oldExchange; } }
Stream based processing
from("direct:streaming") .split(body().tokenize(","), new MyOrderStrategy()) .parallelProcessing() .streaming() .to("activemq:my.parts") .end() .to("activemq:all.parts");
// Java import static org.apache.camel.builder.ExpressionBuilder.beanExpression; ... from("direct:streaming") .split(beanExpression(new MyCustomIteratorFactory(), "iterator")) .streaming().to("activemq:my.parts")
Stream based processing with XML
tokenizeXML
sub-command in streaming mode.
order
elements, you can split the file into order
elements using a route like the following:
from("file:inbox") .split().tokenizeXML("order").streaming() .to("activemq:queue:order");
<route> <from uri="file:inbox"/> <split streaming="true"> <tokenize token="order" xml="true"/> <to uri="activemq:queue:order"/> </split> </route>
tokenizeXML
. For example, to inherit namespace definitions from the enclosing orders
element:
from("file:inbox")
.split().tokenizeXML("order", "orders").streaming()
.to("activemq:queue:order");
inheritNamespaceTagName
attribute. For example:
<route>
<from uri="file:inbox"/>
<split streaming="true">
<tokenize token="order"
xml="true"
inheritNamespaceTagName="orders"/>
<to uri="activemq:queue:order"/>
</split>
</route>
Options
split
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
strategyRef
|
Refers to an AggregationStrategy to be used to assemble the replies from the sub-messages, into a single outgoing message from the Splitter. See the section titled What does the splitter return below for whats used by default. | |
strategyMethodName
|
This option can be used to explicitly specify the method name to use, when using POJOs as the AggregationStrategy .
|
|
strategyMethodAllowNull
|
false
|
This option can be used, when using POJOs as the AggregationStrategy . If false , the aggregate method is not used, when there is no data to enrich. If true , null values are used for the oldExchange , when there is no data to enrich.
|
parallelProcessing
|
false
|
If enables then processing the sub-messages occurs concurrently. Note the caller thread will still wait until all sub-messages has been fully processed, before it continues. |
parallelAggregate
|
false
|
If enabled, the aggregate method on AggregationStrategy can be called concurrently. Note that this requires the implementation of AggregationStrategy to be thread-safe. By default, this option is false , which means that Camel automatically synchronizes calls to the aggregate method. In some use-cases, however, you can improve performance by implementing AggregationStrategy as thread-safe and setting this option to true .
|
executorServiceRef
|
Refers to a custom Thread Pool to be used for parallel processing. Notice if you set this option, then parallel processing is automatic implied, and you do not have to enable that option as well. | |
stopOnException
|
false
|
Camel 2.2: Whether or not to stop continue processing immediately when an exception occurred. If disable, then Camel continue splitting and process the sub-messages regardless if one of them failed. You can deal with exceptions in the AggregationStrategy class where you have full control how to handle that. |
streaming
|
false
|
If enabled then Camel will split in a streaming fashion, which means it will split the input message in chunks. This reduces the memory overhead. For example if you split big messages its recommended to enable streaming. If streaming is enabled then the sub-message replies will be aggregated out-of-order, eg in the order they come back. If disabled, Camel will process sub-message replies in the same order as they where splitted. |
timeout
|
Camel 2.5: Sets a total timeout specified in millis. If the Recipient List hasn't been able to split and process all replies within the given timeframe, then the timeout triggers and the Splitter breaks out and continues. Notice if you provide a TimeoutAwareAggregationStrategy then the timeout method is invoked before breaking out.
|
|
onPrepareRef
|
Camel 2.8: Refers to a custom Processor to prepare the sub-message of the Exchange, before its processed. This allows you to do any custom logic, such as deep-cloning the message payload if that's needed etc. | |
shareUnitOfWork
|
false
|
Camel 2.8: Whether the unit of work should be shared. See further below for more details. |
8.5. Aggregator
Overview
Figure 8.5. Aggregator Pattern
- Correlation expression — Determines which messages should be aggregated together. The correlation expression is evaluated on each incoming message to produce a correlation key. Incoming messages with the same correlation key are then grouped into the same batch. For example, if you want to aggregate all incoming messages into a single message, you can use a constant expression.
- Completeness condition — Determines when a batch of messages is complete. You can specify this either as a simple size limit or, more generally, you can specify a predicate condition that flags when the batch is complete.
- Aggregation algorithm — Combines the message exchanges for a single correlation key into a single message exchange.
How the aggregator works
Figure 8.6. Aggregator Implementation
- The correlator is responsible for sorting exchanges based on the correlation key. For each incoming exchange, the correlation expression is evaluated, yielding the correlation key. For example, for the exchange shown in Figure 8.6, “Aggregator Implementation”, the correlation key evaluates to A.
- The aggregation strategy is responsible for merging exchanges with the same correlation key. When a new exchange, A, comes in, the aggregator looks up the corresponding aggregate exchange, A', in the aggregation repository and combines it with the new exchange.Until a particular aggregation cycle is completed, incoming exchanges are continuously aggregated with the corresponding aggregate exchange. An aggregation cycle lasts until terminated by one of the completion mechanisms.
- If a completion predicate is specified on the aggregator, the aggregate exchange is tested to determine whether it is ready to be sent to the next processor in the route. Processing continues as follows:
- If complete, the aggregate exchange is processed by the latter part of the route. There are two alternative models for this: synchronous (the default), which causes the calling thread to block, or asynchronous (if parallel processing is enabled), where the aggregate exchange is submitted to an executor thread pool (as shown in Figure 8.6, “Aggregator Implementation”).
- If not complete, the aggregate exchange is saved back to the aggregation repository.
- In parallel with the synchronous completion tests, it is possible to enable an asynchronous completion test by enabling either the
completionTimeout
option or thecompletionInterval
option. These completion tests run in a separate thread and, whenever the completion test is satisfied, the corresponding exchange is marked as complete and starts to be processed by the latter part of the route (either synchronously or asynchronously, depending on whether parallel processing is enabled or not). - If parallel processing is enabled, a thread pool is responsible for processing exchanges in the latter part of the route. By default, this thread pool contains ten threads, but you have the option of customizing the pool (the section called “Threading options”).
Java DSL example
StockSymbol
header value, using the UseLatestAggregationStrategy
aggregation strategy. For a given StockSymbol
value, if more than three seconds elapse since the last exchange with that correlation key was received, the aggregated exchange is deemed to be complete and is sent to the mock
endpoint.
from("direct:start") .aggregate(header("id"), new UseLatestAggregationStrategy()) .completionTimeout(3000) .to("mock:aggregated");
XML DSL example
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <aggregate strategyRef="aggregatorStrategy" completionTimeout="3000"> <correlationExpression> <simple>header.StockSymbol</simple> </correlationExpression> <to uri="mock:aggregated"/> </aggregate> </route> </camelContext> <bean id="aggregatorStrategy" class="org.apache.camel.processor.aggregate.UseLatestAggregationStrategy"/>
Specifying the correlation expression
aggregate()
DSL command. You are not limited to using the Simple expression language here. You can specify a correlation expression using any of the expression languages or scripting languages, such as XPath, XQuery, SQL, and so on.
from("direct:start") .aggregate(xpath("/stockQuote/@symbol"), new UseLatestAggregationStrategy()) .completionTimeout(3000) .to("mock:aggregated");
CamelExchangeException
by default. You can suppress this exception by setting the ignoreInvalidCorrelationKeys
option. For example, in the Java DSL:
from(...).aggregate(...).ignoreInvalidCorrelationKeys()
ignoreInvalidCorrelationKeys
option is set as an attribute, as follows:
<aggregate strategyRef="aggregatorStrategy" ignoreInvalidCorrelationKeys="true" ...> ... </aggregate>
Specifying the aggregation strategy
aggregate()
DSL command or specify it using the aggregationStrategy()
clause. For example, you can use the aggregationStrategy()
clause as follows:
from("direct:start") .aggregate(header("id")) .aggregationStrategy(new UseLatestAggregationStrategy()) .completionTimeout(3000) .to("mock:aggregated");
org.apache.camel.processor.aggregate
Java package):
UseLatestAggregationStrategy
- Return the last exchange for a given correlation key, discarding all earlier exchanges with this key. For example, this strategy could be useful for throttling the feed from a stock exchange, where you just want to know the latest price of a particular stock symbol.
UseOriginalAggregationStrategy
- Return the first exchange for a given correlation key, discarding all later exchanges with this key. You must set the first exchange by calling
UseOriginalAggregationStrategy.setOriginal()
before you can use this strategy. GroupedExchangeAggregationStrategy
- Concatenates all of the exchanges for a given correlation key into a list, which is stored in the
Exchange.GROUPED_EXCHANGE
exchange property. See the section called “Grouped exchanges”.
Implementing a custom aggregation strategy
org.apache.camel.processor.aggregate.AggregationStrategy
- The basic aggregation strategy interface.
org.apache.camel.processor.aggregate.TimeoutAwareAggregationStrategy
- Implement this interface, if you want your implementation to receive a notification when an aggregation cycle times out. The
timeout
notification method has the following signature:void timeout(Exchange oldExchange, int index, int total, long timeout)
org.apache.camel.processor.aggregate.CompletionAwareAggregationStrategy
- Implement this interface, if you want your implementation to receive a notification when an aggregation cycle completes normally. The notification method has the following signature:
void onCompletion(Exchange exchange)
StringAggregationStrategy
and ArrayListAggregationStrategy
::
//simply combines Exchange String body values using '+' as a delimiter class StringAggregationStrategy implements AggregationStrategy { public Exchange aggregate(Exchange oldExchange, Exchange newExchange) { if (oldExchange == null) { return newExchange; } String oldBody = oldExchange.getIn().getBody(String.class); String newBody = newExchange.getIn().getBody(String.class); oldExchange.getIn().setBody(oldBody + "+" + newBody); return oldExchange; } } //simply combines Exchange body values into an ArrayList<Object> class ArrayListAggregationStrategy implements AggregationStrategy { public Exchange aggregate(Exchange oldExchange, Exchange newExchange) { Object newBody = newExchange.getIn().getBody(); ArrayList<Object> list = null; if (oldExchange == null) { list = new ArrayList<Object>(); list.add(newBody); newExchange.getIn().setBody(list); return newExchange; } else { list = oldExchange.getIn().getBody(ArrayList.class); list.add(newBody); return oldExchange; } } }
AggregationStrategy.aggregate()
callback method is also invoked for the very first exchange. On the first invocation of the aggregate
method, the oldExchange
parameter is null
and the newExchange
parameter contains the first incoming exchange.
ArrayListAggregationStrategy
, define a route like the following:
from("direct:start") .aggregate(header("StockSymbol"), new ArrayListAggregationStrategy()) .completionTimeout(3000) .to("mock:result");
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <aggregate strategyRef="aggregatorStrategy" completionTimeout="3000"> <correlationExpression> <simple>header.StockSymbol</simple> </correlationExpression> <to uri="mock:aggregated"/> </aggregate> </route> </camelContext> <bean id="aggregatorStrategy" class="com.my_package_name.ArrayListAggregationStrategy"/>
Controlling the lifecycle of a custom aggregation strategy
org.apache.camel.Service
interface (in addition to the AggregationStrategy
interface) and provide implementations of the start()
and stop()
lifecycle methods. For example, the following code example shows an outline of an aggregation strategy with lifecycle support:
// Java import org.apache.camel.processor.aggregate.AggregationStrategy; import org.apache.camel.Service; import java.lang.Exception; ... class MyAggStrategyWithLifecycleControl implements AggregationStrategy, Service { public Exchange aggregate(Exchange oldExchange, Exchange newExchange) { // Implementation not shown... ... } public void start() throws Exception { // Actions to perform when the enclosing EIP starts up ... } public void stop() throws Exception { // Actions to perform when the enclosing EIP is stopping ... } }
Exchange properties
Header | Type | Description |
---|---|---|
Exchange.AGGREGATED_SIZE
|
int
|
The total number of exchanges aggregated into this exchange. |
Exchange.AGGREGATED_COMPLETED_BY
|
String
|
Indicates the mechanism responsible for completing the aggregate exchange. Possible values are: predicate , size , timeout , interval , or consumer .
|
Header | Type | Description |
---|---|---|
Exchange.REDELIVERY_COUNTER
|
int
|
Sequence number of the current redelivery attempt (starting at 1 ).
|
Specifying a completion condition
completionPredicate
- Evaluates a predicate after each exchange is aggregated in order to determine completeness. A value of
true
indicates that the aggregate exchange is complete. Alternatively, instead of setting this option, you can define a customAggregationStrategy
that implements thePredicate
interface, in which case theAggregationStrategy
will be used as the completion predicate. completionSize
- Completes the aggregate exchange after the specified number of incoming exchanges are aggregated.
completionTimeout
- (Incompatible with
completionInterval
) Completes the aggregate exchange, if no incoming exchanges are aggregated within the specified timeout.In other words, the timeout mechanism keeps track of a timeout for each correlation key value. The clock starts ticking after the latest exchange with a particular key value is received. If another exchange with the same key value is not received within the specified timeout, the corresponding aggregate exchange is marked complete and sent to the next node on the route. completionInterval
- (Incompatible with
completionTimeout
) Completes all outstanding aggregate exchanges, after each time interval (of specified length) has elapsed.The time interval is not tailored to each aggregate exchange. This mechanism forces simultaneous completion of all outstanding aggregate exchanges. Hence, in some cases, this mechanism could complete an aggregate exchange immediately after it started aggregating. completionFromBatchConsumer
- When used in combination with a consumer endpoint that supports the batch consumer mechanism, this completion option automatically figures out when the current batch of exchanges is complete, based on information it receives from the consumer endpoint. See the section called “Batch consumer”.
forceCompletionOnStop
- When this option is enabled, it forces completion of all outstanding aggregate exchanges when the current route context is stopped.
completionTimeout
and completionInterval
conditions, which cannot be simultaneously enabled. When conditions are used in combination, the general rule is that the first completion condition to trigger is the effective completion condition.
Specifying the completion predicate
- On the latest aggregate exchange—this is the default behavior.
- On the latest incoming exchange—this behavior is selected when you enable the
eagerCheckCompletion
option.
ALERT
message (as indicated by the value of a MsgType
header in the latest incoming exchange), you can define a route like the following:
from("direct:start") .aggregate( header("id"), new UseLatestAggregationStrategy() ) .completionPredicate( header("MsgType").isEqualTo("ALERT") ) .eagerCheckCompletion() .to("mock:result");
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <aggregate strategyRef="aggregatorStrategy" eagerCheckCompletion="true"> <correlationExpression> <simple>header.StockSymbol</simple> </correlationExpression> <completionPredicate> <simple>$MsgType = 'ALERT'</simple> </completionPredicate> <to uri="mock:result"/> </aggregate> </route> </camelContext> <bean id="aggregatorStrategy" class="org.apache.camel.processor.aggregate.UseLatestAggregationStrategy"/>
Specifying a dynamic completion timeout
timeout
header in each incoming exchange, you could define a route as follows:
from("direct:start") .aggregate(header("StockSymbol"), new UseLatestAggregationStrategy()) .completionTimeout(header("timeout")) .to("mock:aggregated");
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <aggregate strategyRef="aggregatorStrategy"> <correlationExpression> <simple>header.StockSymbol</simple> </correlationExpression> <completionTimeout> <header>timeout</header> </completionTimeout> <to uri="mock:aggregated"/> </aggregate> </route> </camelContext> <bean id="aggregatorStrategy" class="org.apache.camel.processor.UseLatestAggregationStrategy"/>
null
or 0
.
Specifying a dynamic completion size
mySize
header in each incoming exchange, you could define a route as follows:
from("direct:start") .aggregate(header("StockSymbol"), new UseLatestAggregationStrategy()) .completionSize(header("mySize")) .to("mock:aggregated");
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <aggregate strategyRef="aggregatorStrategy"> <correlationExpression> <simple>header.StockSymbol</simple> </correlationExpression> <completionSize> <header>mySize</header> </completionSize> <to uri="mock:aggregated"/> </aggregate> </route> </camelContext> <bean id="aggregatorStrategy" class="org.apache.camel.processor.UseLatestAggregationStrategy"/>
null
or 0
.
Forcing completion of a single group from within an AggregationStrategy
AggregationStrategy
class, there is a mechanism available to force the completion of the current message group, by setting the Exchange.AGGREGATION_COMPLETE_CURRENT_GROUP
exchange property to true
on the exchange returned from the AggregationStrategy.aggregate()
method. This mechanism only affects the current group: other message groups (with different correlation IDs) are not forced to complete. This mechanism overrides any other completion mechanisms, such as predicate, size, timeout, and so on.
AggregationStrategy
class completes the current group, if the message body size is larger than 5:
// Java public final class MyCompletionStrategy implements AggregationStrategy { @Override public Exchange aggregate(Exchange oldExchange, Exchange newExchange) { if (oldExchange == null) { return newExchange; } String body = oldExchange.getIn().getBody(String.class) + "+" + newExchange.getIn().getBody(String.class); oldExchange.getIn().setBody(body); if (body.length() >= 5) { oldExchange.setProperty(Exchange.AGGREGATION_COMPLETE_CURRENT_GROUP, true); } return oldExchange; } }
Forcing completion of all groups with a special message
Exchange.AGGREGATION_COMPLETE_ALL_GROUPS
- Set to
true
, to force completion of the current aggregation cycle. This message acts purely as a signal and is not included in any aggregation cycle. After processing this signal message, the content of the message is discarded. Exchange.AGGREGATION_COMPLETE_ALL_GROUPS_INCLUSIVE
- Set to
true
, to force completion of the current aggregation cycle. This message is included in the current aggregation cycle.
Enforcing unique correlation keys
closeCorrelationKeyOnCompletion
option. In order to suppress duplicate correlation key values, it is necessary for the aggregator to record previous correlation key values in a cache. The size of this cache (the number of cached correlation keys) is specified as an argument to the closeCorrelationKeyOnCompletion()
DSL command. To specify a cache of unlimited size, you can pass a value of zero or a negative integer. For example, to specify a cache size of 10000
key values:
from("direct:start") .aggregate(header("UniqueBatchID"), new MyConcatenateStrategy()) .completionSize(header("mySize")) .closeCorrelationKeyOnCompletion(10000) .to("mock:aggregated");
ClosedCorrelationKeyException
exception.
Grouped exchanges
org.apache.camel.impl.GroupedExchange
holder class. To enable grouped exchanges, specify the groupExchanges()
option, as shown in the following Java DSL route:
from("direct:start") .aggregate(header("StockSymbol")) .completionTimeout(3000) .groupExchanges() .to("mock:result");
mock:result
contains the list of aggregated exchanges in the message body. The following line of code shows how a subsequent processor can access the contents of the grouped exchange in the form of a list:
// Java List<Exchange> grouped = ex.getIn().getBody(List.class);
Batch consumer
CamelBatchSize
, CamelBatchIndex
, and CamelBatchComplete
properties on the incoming exchange). For example, to aggregate all of the files found by a File consumer endpoint, you could use a route like the following:
from("file://inbox") .aggregate(xpath("//order/@customerId"), new AggregateCustomerOrderStrategy()) .completionFromBatchConsumer() .to("bean:processOrder");
Persistent aggregation repository
camel-hawtdb
component in your Maven POM. You can then configure a route to use the HawtDB aggregation repository as follows:
public void configure() throws Exception { HawtDBAggregationRepository repo = new AggregationRepository("repo1", "target/data/hawtdb.dat"); from("direct:start") .aggregate(header("id"), new UseLatestAggregationStrategy()) .completionTimeout(3000) .aggregationRepository(repo) .to("mock:aggregated"); }
Figure 8.7. Recoverable Aggregation Repository
- The aggregator creates a dedicated recovery thread, which runs in the background, scanning the aggregation repository to find any failed exchanges.
- Each failed exchange is checked to see whether its current redelivery count exceeds the maximum redelivery limit. If it is under the limit, the recovery task resubmits the exchange for processing in the latter part of the route.
- If the current redelivery count is over the limit, the failed exchange is passed to the dead letter queue.
Threading options
parallelProcessing
option, as follows:
from("direct:start") .aggregate(header("id"), new UseLatestAggregationStrategy()) .completionTimeout(3000) .parallelProcessing() .to("mock:aggregated");
java.util.concurrent.ExecutorService
instance using the executorService
option (in which case it is unnecessary to enable the parallelProcessing
option).
Aggregating into a List
List
object. To facilitate this scenario, Apache Camel provides the AbstractListAggregationStrategy
abstract class, which you can quickly extend to create an aggregation strategy for this case. Incoming message bodies of type, T
, are aggregated into a completed exchange, with a message body of type List<T>
.
Integer
message bodies into a List<Integer>
object, you could use an aggregation strategy defined as follows:
import org.apache.camel.processor.aggregate.AbstractListAggregationStrategy; ... /** * Strategy to aggregate integers into a List<Integer>. */ public final class MyListOfNumbersStrategy extends AbstractListAggregationStrategy<Integer> { @Override public Integer getValue(Exchange exchange) { // the message body contains a number, so just return that as-is return exchange.getIn().getBody(Integer.class); } }
Aggregator options
Option | Default | Description |
---|---|---|
correlationExpression | Mandatory Expression which evaluates the correlation key to use for aggregation. The Exchange which has the same correlation key is aggregated together. If the correlation key could not be evaluated an Exception is thrown. You can disable this by using the ignoreBadCorrelationKeys option. | |
aggregationStrategy | Mandatory AggregationStrategy which is used to merge the incoming Exchange with the existing already merged exchanges. At first call the oldExchange parameter is null . On subsequent invocations the oldExchange contains the merged exchanges and newExchange is of course the new incoming Exchange. From Camel 2.9.2 onwards, the strategy can optionally be a TimeoutAwareAggregationStrategy implementation, which supports a timeout callback | |
strategyRef | A reference to lookup the AggregationStrategy in the Registry. | |
completionSize | Number of messages aggregated before the aggregation is complete. This option can be set as either a fixed value or using an Expression which allows you to evaluate a size dynamically - will use Integer as result. If both are set Camel will fallback to use the fixed value if the Expression result was null or 0 . | |
completionTimeout | Time in millis that an aggregated exchange should be inactive before its complete. This option can be set as either a fixed value or using an Expression which allows you to evaluate a timeout dynamically - will use Long as result. If both are set Camel will fallback to use the fixed value if the Expression result was null or 0 . You cannot use this option together with completionInterval, only one of the two can be used. | |
completionInterval | A repeating period in millis by which the aggregator will complete all current aggregated exchanges. Camel has a background task which is triggered every period. You cannot use this option together with completionTimeout, only one of them can be used. | |
completionPredicate | Specifies a predicate (of org.apache.camel.Predicate type), which signals when an aggregated exchange is complete. Alternatively, instead of setting this option, you can define a custom AggregationStrategy that implements the Predicate interface, in which case the AggregationStrategy will be used as the completion predicate. | |
completionFromBatchConsumer | false | This option is if the exchanges are coming from a Batch Consumer. Then when enabled the Aggregator will use the batch size determined by the Batch Consumer in the message header CamelBatchSize . See more details at Batch Consumer. This can be used to aggregate all files consumed from a File endpoint in that given poll. |
eagerCheckCompletion | false | Whether or not to eager check for completion when a new incoming Exchange has been received. This option influences the behavior of the completionPredicate option as the Exchange being passed in changes accordingly. When false the Exchange passed in the Predicate is the aggregated Exchange which means any information you may store on the aggregated Exchange from the AggregationStrategy is available for the Predicate. When true the Exchange passed in the Predicate is the incoming Exchange, which means you can access data from the incoming Exchange. |
forceCompletionOnStop | false | If true , complete all aggregated exchanges when the current route context is stopped. |
groupExchanges | false | If enabled then Camel will group all aggregated Exchanges into a single combined org.apache.camel.impl.GroupedExchange holder class that holds all the aggregated Exchanges. And as a result only one Exchange is being sent out from the aggregator. Can be used to combine many incoming Exchanges into a single output Exchange without coding a custom AggregationStrategy yourself. |
ignoreInvalidCorrelationKeys | false | Whether or not to ignore correlation keys which could not be evaluated to a value. By default Camel will throw an Exception, but you can enable this option and ignore the situation instead. |
closeCorrelationKeyOnCompletion | Whether or not late Exchanges should be accepted or not. You can enable this to indicate that if a correlation key has already been completed, then any new exchanges with the same correlation key be denied. Camel will then throw a closedCorrelationKeyException exception. When using this option you pass in a integer which is a number for a LRUCache which keeps that last X number of closed correlation keys. You can pass in 0 or a negative value to indicate a unbounded cache. By passing in a number you are ensured that cache wont grown too big if you use a log of different correlation keys. | |
discardOnCompletionTimeout | false | Camel 2.5: Whether or not exchanges which complete due to a timeout should be discarded. If enabled, then when a timeout occurs the aggregated message will not be sent out but dropped (discarded). |
aggregationRepository | Allows you to plug in you own implementation of org.apache.camel.spi.AggregationRepository which keeps track of the current inflight aggregated exchanges. Camel uses by default a memory based implementation. | |
aggregationRepositoryRef | Reference to lookup a aggregationRepository in the Registry. | |
parallelProcessing | false | When aggregated are completed they are being send out of the aggregator. This option indicates whether or not Camel should use a thread pool with multiple threads for concurrency. If no custom thread pool has been specified then Camel creates a default pool with 10 concurrent threads. |
executorService | If using parallelProcessing you can specify a custom thread pool to be used. In fact also if you are not using parallelProcessing this custom thread pool is used to send out aggregated exchanges as well. | |
executorServiceRef | Reference to lookup a executorService in the Registry | |
timeoutCheckerExecutorService | If using one of the completionTimeout , completionTimeoutExpression , or completionInterval options, a background thread is created to check for the completion for every aggregator. Set this option to provide a custom thread pool to be used rather than creating a new thread for every aggregator. | |
timeoutCheckerExecutorServiceRef | Reference to look up a timeoutCheckerExecutorService in the registry. | |
optimisticLocking | false | Turns on optimistic locking, which can be used in combination with an aggregation repository. |
optimisticLockRetryPolicy | Configures the retry policy for optimistic locking. |
8.6. Resequencer
Overview
Figure 8.8. Resequencer Pattern
- Batch resequencing — Collects messages into a batch, sorts the messages and sends them to their output.
- Stream resequencing — Re-orders (continuous) message streams based on the detection of gaps between messages.
Batch resequencing
TimeStamp
header, you can define the following route in Java DSL:
from("direct:start").resequence(header("TimeStamp")).to("mock:result");
batch()
DSL command, which takes a BatchResequencerConfig
instance as its sole argument. For example, to modify the preceding route so that the batch consists of messages collected in a 4000 millisecond time window, up to a maximum of 300 messages, you can define the Java DSL route as follows:
import org.apache.camel.model.config.BatchResequencerConfig; RouteBuilder builder = new RouteBuilder() { public void configure() { from("direct:start").resequence(header("TimeStamp")).batch(new BatchResequencerConfig(300,4000L)).to("mock:result"); } };
<camelContext id="resequencerBatch" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start" /> <resequence> <!-- batch-config can be omitted for default (batch) resequencer settings --> <batch-config batchSize="300" batchTimeout="4000" /> <simple>header.TimeStamp</simple> <to uri="mock:result" /> </resequence> </route> </camelContext>
Batch options
Java DSL | XML DSL | Default | Description |
---|---|---|---|
allowDuplicates() | batch-config/@allowDuplicates | false | If true , do not discard duplicate messages from the batch (where duplicate means that the message expression evaluates to the same value). |
reverse() | batch-config/@reverse | false | If true , put the messages in reverse order (where the default ordering applied to a message expression is based on Java's string lexical ordering, as defined by String.compareTo()). |
JMSPriority
, you would need to combine the options, allowDuplicates
and reverse
, as follows:
from("jms:queue:foo") // sort by JMSPriority by allowing duplicates (message can have same JMSPriority) // and use reverse ordering so 9 is first output (most important), and 0 is last // use batch mode and fire every 3th second .resequence(header("JMSPriority")).batch().timeout(3000).allowDuplicates().reverse() .to("mock:result");
Stream resequencing
stream()
to the resequence()
DSL command. For example, to resequence incoming messages based on the value of a sequence number in the seqnum
header, you define a DSL route as follows:
from("direct:start").resequence(header("seqnum")).stream().to("mock:result");
3
has a predecessor message with the sequence number 2
and a successor message with the sequence number 4
. The message sequence 2,3,5
has a gap because the successor of 3
is missing. The resequencer therefore must retain message 5
until message 4
arrives (or a timeout occurs).
StreamResequencerConfig
object as an argument to stream()
. For example, to configure a stream resequencer with a message capacity of 5000 and a timeout of 4000 milliseconds, you define a route as follows:
// Java import org.apache.camel.model.config.StreamResequencerConfig; RouteBuilder builder = new RouteBuilder() { public void configure() { from("direct:start").resequence(header("seqnum")). stream(new StreamResequencerConfig(5000, 4000L)). to("mock:result"); } };
long
, you would must define a custom comparator, as follows:
// Java ExpressionResultComparator<Exchange> comparator = new MyComparator(); StreamResequencerConfig config = new StreamResequencerConfig(5000, 4000L, comparator); from("direct:start").resequence(header("seqnum")).stream(config).to("mock:result");
<camelContext id="resequencerStream" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <resequence> <stream-config capacity="5000" timeout="4000"/> <simple>header.seqnum</simple> <to uri="mock:result" /> </resequence> </route> </camelContext>
Ignore invalid exchanges
CamelExchangeException
exception, if the incoming exchange is not valid—that is, if the sequencing expression cannot be evaluated for some reason (for example, due to a missing header). You can use the ignoreInvalidExchanges
option to ignore these exceptions, which means the resequencer will skip any invalid exchanges.
from("direct:start")
.resequence(header("seqno")).batch().timeout(1000)
// ignore invalid exchanges (they are discarded)
.ignoreInvalidExchanges()
.to("mock:result");
Reject old messages
rejectOld
option can be used to prevent messages being sent out of order, regardless of the mechanism used to resequence messages. When the rejectOld
option is enabled, the resequencer rejects an incoming message (by throwing a MessageRejectedException
exception), if the incoming messages is older (as defined by the current comparator) than the last delivered message.
from("direct:start")
.onException(MessageRejectedException.class).handled(true).to("mock:error").end()
.resequence(header("seqno")).stream().timeout(1000).rejectOld()
.to("mock:result");
8.7. Routing Slip
Overview
Figure 8.9. Routing Slip Pattern
The slip header
cxf:bean:decrypt,cxf:bean:authenticate,cxf:bean:dedup
The current endpoint property
Exchange.SLIP_ENDPOINT
) on the exchange which contains the current endpoint as it advanced though the slip. This enables you to find out how far the exchange has progressed through the slip.
Java DSL example
direct:a
endpoint and reads a routing slip from the aRoutingSlipHeader
header:
from("direct:b").routingSlip("aRoutingSlipHeader");
routingSlip()
. The following example defines a route that uses the aRoutingSlipHeader
header key for the routing slip and uses the #
character as the URI delimiter:
from("direct:c").routingSlip("aRoutingSlipHeader", "#");
XML configuration example
<camelContext id="buildRoutingSlip" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:c"/> <routingSlip uriDelimiter="#"> <headerName>aRoutingSlipHeader</headerName> </routingSlip> </route> </camelContext>
Ignore invalid endpoints
ignoreInvalidEndpoints
, which the Recipient List pattern also supports. You can use it to skip endpoints that are invalid. For example:
from("direct:a").routingSlip("myHeader").ignoreInvalidEndpoints();
ignoreInvalidEndpoints
attribute on the <routingSlip>
tag:
<route> <from uri="direct:a"/> <routingSlip ignoreInvalidEndpoints="true"> <headerName>myHeader</headerName> </routingSlip> </route>
myHeader
contains the two endpoints, direct:foo,xxx:bar
. The first endpoint is valid and works. The second is invalid and, therefore, ignored. Apache Camel logs at INFO
level whenever an invalid endpoint is encountered.
Options
routingSlip
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
uriDelimiter
|
,
|
Delimiter used if the Expression returned multiple endpoints. |
ignoreInvalidEndpoints
|
false
|
If an endpoint uri could not be resolved, should it be ignored. Otherwise Camel will thrown an exception stating the endpoint uri is not valid. |
cacheSize
|
0
|
Camel 2.13.1/2.12.4: Allows to configure the cache size for the ProducerCache which caches producers for reuse in the routing slip. Will by default use the default cache size which is 0. Setting the value to -1 allows to turn off the cache all together. |
8.8. Throttler
Overview
throttle()
Java DSL command.
Java DSL example
from("seda:a").throttle(100).to("seda:b");
timePeriodMillis()
DSL command. For example, to limit the flow rate to 3 messages per 30000 milliseconds, define a route as follows:
from("seda:a").throttle(3).timePeriodMillis(30000).to("mock:result");
XML configuration example
<camelContext id="throttleRoute" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <!-- throttle 3 messages per 30 sec --> <throttle timePeriodMillis="30000"> <constant>3</constant> <to uri="mock:result"/> </throttle> </route> </camelContext>
Dynamically changing maximum requests per period
java.lang.Long
type. In the example below we use a header from the message to determine the maximum requests per period. If the header is absent, then the Throttler uses the old value. So that allows you to only provide a header if the value is to be changed:
<camelContext id="throttleRoute" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:expressionHeader"/> <throttle timePeriodMillis="500"> <!-- use a header to determine how many messages to throttle per 0.5 sec --> <header>throttleValue</header> <to uri="mock:result"/> </throttle> </route> </camelContext>
Asynchronous delaying
from("seda:a").throttle(100).asyncDelayed().to("seda:b");
Options
throttle
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
maximumRequestsPerPeriod
|
Maximum number of requests per period to throttle. This option must be provided and a positive number. Notice, in the XML DSL, from Camel 2.8 onwards this option is configured using an Expression instead of an attribute. | |
timePeriodMillis
|
1000
|
The time period in millis, in which the throttler will allow at most maximumRequestsPerPeriod number of messages.
|
asyncDelayed
|
false
|
Camel 2.4: If enabled then any messages which is delayed happens asynchronously using a scheduled thread pool. |
executorServiceRef
|
Camel 2.4: Refers to a custom Thread Pool to be used if asyncDelay has been enabled.
|
|
callerRunsWhenRejected
|
true
|
Camel 2.4: Is used if asyncDelayed was enabled. This controls if the caller thread should execute the task if the thread pool rejected the task.
|
8.9. Delayer
Overview
Java DSL example
delay()
command to add a relative time delay, in units of milliseconds, to incoming messages. For example, the following route delays all incoming messages by 2 seconds:
from("seda:a").delay(2000).to("mock:result");
from("seda:a").delay(header("MyDelay")).to("mock:result");
delay()
are interpreted as sub-clauses of delay()
. Hence, in some contexts it is necessary to terminate the sub-clauses of delay() by inserting the end()
command. For example, when delay()
appears inside an onException()
clause, you would terminate it as follows:
from("direct:start") .onException(Exception.class) .maximumRedeliveries(2) .backOffMultiplier(1.5) .handled(true) .delay(1000) .log("Halting for some time") .to("mock:halt") .end() .end() .to("mock:result");
XML configuration example
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <delay> <header>MyDelay</header> </delay> <to uri="mock:result"/> </route> <route> <from uri="seda:b"/> <delay> <constant>1000</constant> </delay> <to uri="mock:result"/> </route> </camelContext>
Creating a custom delay
from("activemq:foo"). delay().expression().method("someBean", "computeDelay"). to("activemq:bar");
public class SomeBean { public long computeDelay() { long delay = 0; // use java code to compute a delay value in millis return delay; } }
Asynchronous delaying
from("activemq:queue:foo") .delay(1000) .asyncDelayed() .to("activemq:aDelayedQueue");
<route> <from uri="activemq:queue:foo"/> <delay asyncDelayed="true"> <constant>1000</constant> </delay> <to uri="activemq:aDealyedQueue"/> </route>
Options
Name | Default Value | Description |
---|---|---|
asyncDelayed
|
false
|
Camel 2.4: If enabled then delayed messages happens asynchronously using a scheduled thread pool. |
executorServiceRef
|
Camel 2.4: Refers to a custom Thread Pool to be used if asyncDelay has been enabled.
|
|
callerRunsWhenRejected
|
true
|
Camel 2.4: Is used if asyncDelayed was enabled. This controls if the caller thread should execute the task if the thread pool rejected the task.
|
8.10. Load Balancer
Overview
Java DSL example
mock:x
, mock:y
, mock:z
, using a round robin load-balancing policy:
from("direct:start").loadBalance().roundRobin().to("mock:x", "mock:y", "mock:z");
XML configuration example
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <loadBalance> <roundRobin/> <to uri="mock:x"/> <to uri="mock:y"/> <to uri="mock:z"/> </loadBalance> </route> </camelContext>
Load-balancing policies
Round robin
mock:x
, mock:y
, mock:z
, then the incoming messages are sent to the following sequence of endpoints: mock:x
, mock:y
, mock:z
, mock:x
, mock:y
, mock:z
, and so on.
from("direct:start").loadBalance().roundRobin().to("mock:x", "mock:y", "mock:z");
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <loadBalance> <roundRobin/> <to uri="mock:x"/> <to uri="mock:y"/> <to uri="mock:z"/> </loadBalance> </route> </camelContext>
Random
from("direct:start").loadBalance().random().to("mock:x", "mock:y", "mock:z");
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <loadBalance> <random/> <to uri="mock:x"/> <to uri="mock:y"/> <to uri="mock:z"/> </loadBalance> </route> </camelContext>
Sticky
from("direct:start").loadBalance().sticky(header("username")).to("mock:x", "mock:y", "mock:z");
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <loadBalance> <sticky> <expression> <simple>header.username</simple> </expression> </sticky> <to uri="mock:x"/> <to uri="mock:y"/> <to uri="mock:z"/> </loadBalance> </route> </camelContext>
Topic
from("direct:start").loadBalance().topic().to("mock:x", "mock:y", "mock:z");
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <loadBalance> <topic/> <to uri="mock:x"/> <to uri="mock:y"/> <to uri="mock:z"/> </loadBalance> </route> </camelContext>
Failover
failover
load balancer is capable of trying the next processor in case an Exchange failed with an exception
during processing. You can configure the failover
with a list of specific exceptions that trigger failover. If you do not specify any exceptions, failover is triggered by any exception. The failover load balancer uses the same strategy for matching exceptions as the onException
exception clause.
failover
load balancer supports the following options:
Option | Type | Default | Description |
---|---|---|---|
inheritErrorHandler
|
boolean
|
true
|
Camel 2.3: Specifies whether to use the
errorHandler configured on the route. If you want to fail over immediately to the next endpoint, you should disable this option (value of false ). If you enable this option, Apache Camel will first attempt to process the message using the errorHandler .
For example, the
errorHandler might be configured to redeliver messages and use delays between attempts. Apache Camel will initially try to redeliver to the original endpoint, and only fail over to the next endpoint when the errorHandler is exhausted.
|
maximumFailoverAttempts
|
int
|
-1
|
Camel 2.3: Specifies the maximum number of attempts to fail over to a new endpoint. The value,
0 , implies that no failover attempts are made and the value, -1 , implies an infinite number of failover attempts.
|
roundRobin
|
boolean
|
false
|
Camel 2.3: Specifies whether the
failover load balancer should operate in round robin mode or not. If not, it will always start from the first endpoint when a new message is to be processed. In other words it restarts from the top for every message. If round robin is enabled, it keeps state and continues with the next endpoint in a round robin fashion. When using round robin it will not stick to last known good endpoint, it will always pick the next endpoint to use.
|
IOException
exception is thrown:
from("direct:start") // here we will load balance if IOException was thrown // any other kind of exception will result in the Exchange as failed // to failover over any kind of exception we can just omit the exception // in the failOver DSL .loadBalance().failover(IOException.class) .to("direct:x", "direct:y", "direct:z");
// enable redelivery so failover can react errorHandler(defaultErrorHandler().maximumRedeliveries(5)); from("direct:foo") .loadBalance() .failover(IOException.class, MyOtherException.class) .to("direct:a", "direct:b");
<route errorHandlerRef="myErrorHandler"> <from uri="direct:foo"/> <loadBalance> <failover> <exception>java.io.IOException</exception> <exception>com.mycompany.MyOtherException</exception> </failover> <to uri="direct:a"/> <to uri="direct:b"/> </loadBalance> </route>
from("direct:start") // Use failover load balancer in stateful round robin mode, // which means it will fail over immediately in case of an exception // as it does NOT inherit error handler. It will also keep retrying, as // it is configured to retry indefinitely. .loadBalance().failover(-1, false, true) .to("direct:bad", "direct:bad2", "direct:good", "direct:good2");
<route> <from uri="direct:start"/> <loadBalance> <!-- failover using stateful round robin, which will keep retrying the 4 endpoints indefinitely. You can set the maximumFailoverAttempt to break out after X attempts --> <failover roundRobin="true"/> <to uri="direct:bad"/> <to uri="direct:bad2"/> <to uri="direct:good"/> <to uri="direct:good2"/> </loadBalance> </route>
Weighted round robin and weighted random
Option | Type | Default | Description |
---|---|---|---|
roundRobin
|
boolean
|
false
|
The default value for round-robin is false . In the absence of this setting or parameter, the load-balancing algorithm used is random.
|
distributionRatioDelimiter
|
String
|
, |
The distributionRatioDelimiter is the delimiter used to specify the distributionRatio . If this attribute is not specified, comma , is the default delimiter.
|
// Java // round-robin from("direct:start") .loadBalance().weighted(true, "4:2:1" distributionRatioDelimiter=":") .to("mock:x", "mock:y", "mock:z"); //random from("direct:start") .loadBalance().weighted(false, "4,2,1") .to("mock:x", "mock:y", "mock:z");
<!-- round-robin --> <route> <from uri="direct:start"/> <loadBalance> <weighted roundRobin="true" distributionRatio="4:2:1" distributionRatioDelimiter=":" /> <to uri="mock:x"/> <to uri="mock:y"/> <to uri="mock:z"/> </loadBalance> </route>
Custom Load Balancer
from("direct:start") // using our custom load balancer .loadBalance(new MyLoadBalancer()) .to("mock:x", "mock:y", "mock:z");
<!-- this is the implementation of our custom load balancer --> <bean id="myBalancer" class="org.apache.camel.processor.CustomLoadBalanceTest$MyLoadBalancer"/> <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <loadBalance> <!-- refer to my custom load balancer --> <custom ref="myBalancer"/> <!-- these are the endpoints to balancer --> <to uri="mock:x"/> <to uri="mock:y"/> <to uri="mock:z"/> </loadBalance> </route> </camelContext>
<loadBalance ref="myBalancer"> <!-- these are the endpoints to balancer --> <to uri="mock:x"/> <to uri="mock:y"/> <to uri="mock:z"/> </loadBalance>
LoadBalancerSupport
and SimpleLoadBalancerSupport
. The former supports the asynchronous routing engine, and the latter does not. Here is an example:
public static class MyLoadBalancer extends LoadBalancerSupport { public boolean process(Exchange exchange, AsyncCallback callback) { String body = exchange.getIn().getBody(String.class); try { if ("x".equals(body)) { getProcessors().get(0).process(exchange); } else if ("y".equals(body)) { getProcessors().get(1).process(exchange); } else { getProcessors().get(2).process(exchange); } } catch (Throwable e) { exchange.setException(e); } callback.done(true); return true; } }
Circuit Breaker
halfOpenAfter
timeout is reached. After the timeout, if there is a new call, the Circuit Breaker passes all the messages. If the result is success, the Circuit Breaker moves to a closed state, if not, it moves back to open state.
from("direct:start").loadBalance() .circuitBreaker(2, 1000L, MyCustomException.class) .to("mock:result");
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <loadBalance> <circuitBreaker threshold="2" halfOpenAfter="1000"> <exception>MyCustomException</exception> </circuitBreaker> <to uri="mock:result"/> </loadBalance> </route> </camelContext>
8.11. Multicast
Overview
Figure 8.10. Multicast Pattern
Multicast with a custom aggregation strategy
multicast()
DSL command, as follows:
from("cxf:bean:offer").multicast(new HighestBidAggregationStrategy()). to("cxf:bean:Buyer1", "cxf:bean:Buyer2", "cxf:bean:Buyer3");
cxf:bean:offer
, and the buyers are represented by the endpoints, cxf:bean:Buyer1
, cxf:bean:Buyer2
, cxf:bean:Buyer3
. To consolidate the bids received from the various buyers, the multicast processor uses the aggregation strategy, HighestBidAggregationStrategy
. You can implement the HighestBidAggregationStrategy
in Java, as follows:
// Java import org.apache.camel.processor.aggregate.AggregationStrategy; import org.apache.camel.Exchange; public class HighestBidAggregationStrategy implements AggregationStrategy { public Exchange aggregate(Exchange oldExchange, Exchange newExchange) { float oldBid = oldExchange.getOut().getHeader("Bid", Float.class); float newBid = newExchange.getOut().getHeader("Bid", Float.class); return (newBid > oldBid) ? newExchange : oldExchange; } }
Bid
. For more details about custom aggregation strategies, see Section 8.5, “Aggregator”.
Parallel processing
to()
command). In some cases, this might cause unacceptably long latency. To avoid these long latency times, you have the option of enabling parallel processing by adding the parallelProcessing()
clause. For example, to enable parallel processing in the electronic auction example, define the route as follows:
from("cxf:bean:offer") .multicast(new HighestBidAggregationStrategy()) .parallelProcessing() .to("cxf:bean:Buyer1", "cxf:bean:Buyer2", "cxf:bean:Buyer3");
executorService()
method to specify your own custom executor service. For example:
from("cxf:bean:offer") .multicast(new HighestBidAggregationStrategy()) .executorService(MyExecutor) .to("cxf:bean:Buyer1", "cxf:bean:Buyer2", "cxf:bean:Buyer3");
MyAggregationStrategy
, is used to aggregate the replies from the endpoints, direct:a
, direct:b
, and direct:c
:
from("direct:start") .multicast(new MyAggregationStrategy()) .parallelProcessing() .timeout(500) .to("direct:a", "direct:b", "direct:c") .end() .to("mock:result");
XML configuration example
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd "> <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="cxf:bean:offer"/> <multicast strategyRef="highestBidAggregationStrategy" parallelProcessing="true" threadPoolRef="myThreadExcutor"> <to uri="cxf:bean:Buyer1"/> <to uri="cxf:bean:Buyer2"/> <to uri="cxf:bean:Buyer3"/> </multicast> </route> </camelContext> <bean id="highestBidAggregationStrategy" class="com.acme.example.HighestBidAggregationStrategy"/> <bean id="myThreadExcutor" class="com.acme.example.MyThreadExcutor"/> </beans>
parallelProcessing
attribute and the threadPoolRef
attribute are optional. It is only necessary to set them if you want to customize the threading behavior of the multicast processor.
Apply custom processing to the outgoing messages
onPrepare
DSL command in the multicast
clause. The onPrepare
command inserts a custom processor just after the message has been shallow-copied and just before the message is dispatched to its endpoint. For example, in the following route, the CustomProc
processor is invoked on the message sent to direct:a
and the CustomProc
processor is also invoked on the message sent to direct:b
.
from("direct:start") .multicast().onPrepare(new CustomProc()) .to("direct:a").to("direct:b");
onPrepare
DSL command is to perform a deep copy of some or all elements of a message. For example, the following CustomProc
processor class performs a deep copy of the message body, where the message body is presumed to be of type, BodyType
, and the deep copy is performed by the method, BodyType.deepCopy()
.
// Java import org.apache.camel.*; ... public class CustomProc implements Processor { public void process(Exchange exchange) throws Exception { BodyType body = exchange.getIn().getBody(BodyType.class); // Make a _deep_ copy of of the body object BodyType clone = BodyType.deepCopy(); exchange.getIn().setBody(clone); // Headers and attachments have already been // shallow-copied. If you need deep copies, // add some more code here. } }
multicast
syntax allows you to invoke the process
DSL command in the multicast
clause, this does not make sense semantically and it does not have the same effect as onPrepare
(in fact, in this context, the process
DSL command has no effect).
Using onPrepare to execute custom logic when preparing messages
onPrepare
which allows you to do this using the Processor interface.
onPrepare
can be used for any kind of custom logic which you would like to execute before the Exchange
is being multicasted.
public class Animal implements Serializable { private int id; private String name; public Animal() { } public Animal(int id, String name) { this.id = id; this.name = name; } public Animal deepClone() { Animal clone = new Animal(); clone.setId(getId()); clone.setName(getName()); return clone; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return id + " " + name; } }
public class AnimalDeepClonePrepare implements Processor { public void process(Exchange exchange) throws Exception { Animal body = exchange.getIn().getBody(Animal.class); // do a deep clone of the body which wont affect when doing multicasting Animal clone = body.deepClone(); exchange.getIn().setBody(clone); } }
onPrepare
option as shown:
from("direct:start") .multicast().onPrepare(new AnimalDeepClonePrepare()).to("direct:a").to("direct:b");
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <!-- use on prepare with multicast --> <multicast onPrepareRef="animalDeepClonePrepare"> <to uri="direct:a"/> <to uri="direct:b"/> </multicast> </route> <route> <from uri="direct:a"/> <process ref="processorA"/> <to uri="mock:a"/> </route> <route> <from uri="direct:b"/> <process ref="processorB"/> <to uri="mock:b"/> </route> </camelContext> <!-- the on prepare Processor which performs the deep cloning --> <bean id="animalDeepClonePrepare" class="org.apache.camel.processor.AnimalDeepClonePrepare"/> <!-- processors used for the last two routes, as part of unit test --> <bean id="processorA" class="org.apache.camel.processor.MulticastOnPrepareTest$ProcessorA"/> <bean id="processorB" class="org.apache.camel.processor.MulticastOnPrepareTest$ProcessorB"/>
Options
multicast
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
strategyRef
|
Refers to an AggregationStrategy to be used to assemble the replies from the multicasts, into a single outgoing message from the Multicast. By default Camel will use the last reply as the outgoing message. | |
strategyMethodName
|
This option can be used to explicitly specify the method name to use, when using POJOs as the AggregationStrategy .
|
|
strategyMethodAllowNull
|
false
|
This option can be used, when using POJOs as the AggregationStrategy . If false , the aggregate method is not used, when there is no data to enrich. If true , null values are used for the oldExchange , when there is no data to enrich.
|
parallelProcessing
|
false
|
If enabled, sending messages to the multicasts occurs concurrently. Note the caller thread will still wait until all messages has been fully processed, before it continues. Its only the sending and processing the replies from the multicasts which happens concurrently. |
parallelAggregate
|
false
|
If enabled, the aggregate method on AggregationStrategy can be called concurrently. Note that this requires the implementation of AggregationStrategy to be thread-safe. By default, this option is false , which means that Camel automatically synchronizes calls to the aggregate method. In some use-cases, however, you can improve performance by implementing AggregationStrategy as thread-safe and setting this option to true .
|
executorServiceRef
|
Refers to a custom Thread Pool to be used for parallel processing. Notice if you set this option, then parallel processing is automatic implied, and you do not have to enable that option as well. | |
stopOnException
|
false
|
Camel 2.2: Whether or not to stop continue processing immediately when an exception occurred. If disable, then Camel will send the message to all multicasts regardless if one of them failed. You can deal with exceptions in the AggregationStrategy class where you have full control how to handle that. |
streaming
|
false
|
If enabled then Camel will process replies out-of-order, eg in the order they come back. If disabled, Camel will process replies in the same order as multicasted. |
timeout
|
Camel 2.5: Sets a total timeout specified in millis. If the Multicast hasn't been able to send and process all replies within the given timeframe, then the timeout triggers and the Multicast breaks out and continues. Notice if you provide a TimeoutAwareAggregationStrategy then the timeout method is invoked before breaking out.
|
|
onPrepareRef
|
Camel 2.8: Refers to a custom Processor to prepare the copy of the Exchange each multicast will receive. This allows you to do any custom logic, such as deep-cloning the message payload if that's needed etc. | |
shareUnitOfWork
|
false
|
Camel 2.8: Whether the unit of work should be shared. See the same option on Splitter for more details. |
8.12. Composed Message Processor
Composed Message Processor
Figure 8.11. Composed Message Processor Pattern
Java DSL example
// split up the order so individual OrderItems can be validated by the appropriate bean from("direct:start") .split().body() .choice() .when().method("orderItemHelper", "isWidget") .to("bean:widgetInventory") .otherwise() .to("bean:gadgetInventory") .end() .to("seda:aggregate"); // collect and re-assemble the validated OrderItems into an order again from("seda:aggregate") .aggregate(new MyOrderAggregationStrategy()) .header("orderId") .completionTimeout(1000L) .to("mock:result");
XML DSL example
<route> <from uri="direct:start"/> <split> <simple>body</simple> <choice> <when> <method bean="orderItemHelper" method="isWidget"/> <to uri="bean:widgetInventory"/> </when> <otherwise> <to uri="bean:gadgetInventory"/> </otherwise> </choice> <to uri="seda:aggregate"/> </split> </route> <route> <from uri="seda:aggregate"/> <aggregate strategyRef="myOrderAggregatorStrategy" completionTimeout="1000"> <correlationExpression> <simple>header.orderId</simple> </correlationExpression> <to uri="mock:result"/> </aggregate> </route>
Processing steps
OrderItems
to a Content Based Router, which routes messages based on the item type. Widget items get sent for checking in the widgetInventory
bean and gadget items get sent to the gadgetInventory
bean. Once these OrderItems
have been validated by the appropriate bean, they are sent on to the Aggregator which collects and re-assembles the validated OrderItems
into an order again.
.header("orderId")
qualifier on the aggregate()
DSL command instructs the aggregator to use the header with the key, orderId
, as the correlation expression.
8.13. Scatter-Gather
Scatter-Gather
Figure 8.12. Scatter-Gather Pattern
Dynamic scatter-gather example
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <recipientList> <header>listOfVendors</header> </recipientList> </route> <route> <from uri="seda:quoteAggregator"/> <aggregate strategyRef="aggregatorStrategy" completionTimeout="1000"> <correlationExpression> <header>quoteRequestId</header> </correlationExpression> <to uri="mock:result"/> </aggregate> </route> </camelContext>
listOfVendors
header to obtain the list of recipients. Hence, the client that sends messages to this application needs to add a listOfVendors
header to the message. Example 8.1, “Messaging Client Sample” shows some sample code from a messaging client that adds the relevant header data to outgoing messages.
Example 8.1. Messaging Client Sample
Map<String, Object> headers = new HashMap<String, Object>(); headers.put("listOfVendors", "bean:vendor1, bean:vendor2, bean:vendor3"); headers.put("quoteRequestId", "quoteRequest-1"); template.sendBodyAndHeaders("direct:start", "<quote_request item=\"beer\"/>", headers);
bean:vendor1
, bean:vendor2
, and bean:vendor3
. These beans are all implemented by the following class:
public class MyVendor { private int beerPrice; @Produce(uri = "seda:quoteAggregator") private ProducerTemplate quoteAggregator; public MyVendor(int beerPrice) { this.beerPrice = beerPrice; } public void getQuote(@XPath("/quote_request/@item") String item, Exchange exchange) throws Exception { if ("beer".equals(item)) { exchange.getIn().setBody(beerPrice); quoteAggregator.send(exchange); } else { throw new Exception("No quote available for " + item); } } }
vendor1
, vendor2
, and vendor3
, are instantiated using Spring XML syntax, as follows:
<bean id="aggregatorStrategy" class="org.apache.camel.spring.processor.scattergather.LowestQuoteAggregationStrategy"/> <bean id="vendor1" class="org.apache.camel.spring.processor.scattergather.MyVendor"> <constructor-arg> <value>1</value> </constructor-arg> </bean> <bean id="vendor2" class="org.apache.camel.spring.processor.scattergather.MyVendor"> <constructor-arg> <value>2</value> </constructor-arg> </bean> <bean id="vendor3" class="org.apache.camel.spring.processor.scattergather.MyVendor"> <constructor-arg> <value>3</value> </constructor-arg> </bean>
MyVendor.getQuote
method. This method does a simple check to see whether this quote request is for beer and then sets the price of beer on the exchange for retrieval at a later step. The message is forwarded to the next step using POJO Producing (see the @Produce annotation).
quoteRequestId
header (passed to the correlationExpression
). As shown in Example 8.1, “Messaging Client Sample”, the correlation ID is set to quoteRequest-1
(the correlation ID should be unique). To pick the lowest quote out of the set, you can use a custom aggregation strategy like the following:
public class LowestQuoteAggregationStrategy implements AggregationStrategy { public Exchange aggregate(Exchange oldExchange, Exchange newExchange) { // the first time we only have the new exchange if (oldExchange == null) { return newExchange; } if (oldExchange.getIn().getBody(int.class) < newExchange.getIn().getBody(int.class)) { return oldExchange; } else { return newExchange; } } }
Static scatter-gather example
from("direct:start").multicast().to("seda:vendor1", "seda:vendor2", "seda:vendor3"); from("seda:vendor1").to("bean:vendor1").to("seda:quoteAggregator"); from("seda:vendor2").to("bean:vendor2").to("seda:quoteAggregator"); from("seda:vendor3").to("bean:vendor3").to("seda:quoteAggregator"); from("seda:quoteAggregator") .aggregate(header("quoteRequestId"), new LowestQuoteAggregationStrategy()).to("mock:result")
8.14. Loop
Loop
Exchange properties
Property | Description |
---|---|
CamelLoopSize
|
Apache Camel 2.0: Total number of loops |
CamelLoopIndex
|
Apache Camel 2.0: Index of the current iteration (0 based) |
Java DSL examples
direct:x
endpoint and then send the message repeatedly to mock:result
. The number of loop iterations is specified either as an argument to loop()
or by evaluating an expression at run time, where the expression must evaluate to an int
(or else a RuntimeCamelException
is thrown).
from("direct:a").loop(8).to("mock:result");
from("direct:b").loop(header("loop")).to("mock:result");
from("direct:c").loop().xpath("/hello/@times").to("mock:result");
XML configuration example
<route> <from uri="direct:a"/> <loop> <constant>8</constant> <to uri="mock:result"/> </loop> </route>
<route> <from uri="direct:b"/> <loop> <header>loop</header> <to uri="mock:result"/> </loop> </route>
Using copy mode
direct:start
endpoint containing the letter A. The output of processing this route will be that, each mock:loop
endpoint will receive AB as message.
from("direct:start") // instruct loop to use copy mode, which mean it will use a copy of the input exchange // for each loop iteration, instead of keep using the same exchange all over .loop(3).copy() .transform(body().append("B")) .to("mock:loop") .end() .to("mock:result");
mock:loop
will receive AB, ABB, ABBB messages.
from("direct:start") // by default loop will keep using the same exchange so on the 2nd and 3rd iteration its // the same exchange that was previous used that are being looped all over .loop(3) .transform(body().append("B")) .to("mock:loop") .end() .to("mock:result");
<route> <from uri="direct:start"/> <!-- enable copy mode for loop eip --> <loop copy="true"> <constant>3</constant> <transform> <simple>${body}B</simple> </transform> <to uri="mock:loop"/> </loop> <to uri="mock:result"/> </route>
Options
loop
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
copy
|
false
|
Camel 2.8: Whether or not copy mode is used. If false then the same Exchange is being used throughout the looping. So the result from the previous iteration will be visible for the next iteration. Instead you can enable copy mode, and then each iteration is restarting with a fresh copy of the input Exchange.
|
8.15. Sampling
Sampling Throttler
Java DSL example
sample()
DSL command to invoke the sampler as follows:
// Sample with default sampling period (1 second) from("direct:sample") .sample() .to("mock:result"); // Sample with explicitly specified sample period from("direct:sample-configured") .sample(1, TimeUnit.SECONDS) .to("mock:result"); // Alternative syntax for specifying sampling period from("direct:sample-configured-via-dsl") .sample().samplePeriod(1).timeUnits(TimeUnit.SECONDS) .to("mock:result"); from("direct:sample-messageFrequency") .sample(10) .to("mock:result"); from("direct:sample-messageFrequency-via-dsl") .sample().sampleMessageFrequency(5) .to("mock:result");
Spring XML example
samplePeriod
and units
attributes:
<route> <from uri="direct:sample"/> <sample samplePeriod="1" units="seconds"> <to uri="mock:result"/> </sample> </route> <route> <from uri="direct:sample-messageFrequency"/> <sample messageFrequency="10"> <to uri="mock:result"/> </sample> </route> <route> <from uri="direct:sample-messageFrequency-via-dsl"/> <sample messageFrequency="5"> <to uri="mock:result"/> </sample> </route>
Options
sample
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
messageFrequency
|
Samples the message every N'th message. You can only use either frequency or period. | |
samplePeriod
|
1
|
Samples the message every N'th period. You can only use either frequency or period. |
units
|
SECOND
|
Time unit as an enum of java.util.concurrent.TimeUnit from the JDK.
|
8.16. Dynamic Router
Dynamic Router
Figure 8.13. Dynamic Router Pattern
dynamicRouter
in the DSL, which is like a dynamic Routing Slip that evaluates the slip on-the-fly.
dynamicRouter
(such as a bean), returns null
to indicate the end. Otherwise, the dynamicRouter
will continue in an endless loop.
Dynamic Router in Camel 2.5 onwards
Exchange.SLIP_ENDPOINT
, with the current endpoint as it advances through the slip. This enables you to find out how far the exchange has progressed through the slip. (It's a slip because the Dynamic Router implementation is based on Routing Slip).
Java DSL
dynamicRouter
as follows:
from("direct:start") // use a bean as the dynamic router .dynamicRouter(bean(DynamicRouterTest.class, "slip"));
// Java /** * Use this method to compute dynamic where we should route next. * * @param body the message body * @return endpoints to go, or <tt>null</tt> to indicate the end */ public String slip(String body) { bodies.add(body); invoked++; if (invoked == 1) { return "mock:a"; } else if (invoked == 2) { return "mock:b,mock:c"; } else if (invoked == 3) { return "direct:foo"; } else if (invoked == 4) { return "mock:result"; } // no more so return null return null; }
Exchange
to ensure thread safety.
Spring XML
<bean id="mySlip" class="org.apache.camel.processor.DynamicRouterTest"/> <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <dynamicRouter> <!-- use a method call on a bean as dynamic router --> <method ref="mySlip" method="slip"/> </dynamicRouter> </route> <route> <from uri="direct:foo"/> <transform><constant>Bye World</constant></transform> <to uri="mock:foo"/> </route> </camelContext>
Options
dynamicRouter
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
uriDelimiter
|
,
|
Delimiter used if the Expression returned multiple endpoints. |
ignoreInvalidEndpoints
|
false
|
If an endpoint uri could not be resolved, should it be ignored. Otherwise Camel will thrown an exception stating the endpoint uri is not valid. |
@DynamicRouter annotation
@DynamicRouter
annotation. For example:
// Java public class MyDynamicRouter { @Consume(uri = "activemq:foo") @DynamicRouter public String route(@XPath("/customer/id") String customerId, @Header("Location") String location, Document body) { // query a database to find the best match of the endpoint based on the input parameteres // return the next endpoint uri, where to go. Return null to indicate the end. } }
route
method is invoked repeatedly as the message progresses through the slip. The idea is to return the endpoint URI of the next destination. Return null
to indicate the end. You can return multiple endpoints if you like, just as the Routing Slip, where each endpoint is separated by a delimiter.
Chapter 9. Message Transformation
Abstract
9.1. Content Enricher
Overview
Figure 9.1. Content Enricher Pattern
Models of content enrichment
enrich()
—obtains additional data from the resource by sending a copy of the current exchange to a producer endpoint and then using the data from the resulting reply (the exchange created by the enricher is always an InOut exchange).pollEnrich()
—obtains the additional data by polling a consumer endpoint for data. Effectively, the consumer endpoint from the main route and the consumer endpoint inpollEnrich()
are coupled, such that exchanges incoming on the main route trigger a poll of thepollEnrich()
endpoint.
Content enrichment using enrich()
AggregationStrategy aggregationStrategy = ... from("direct:start") .enrich("direct:resource", aggregationStrategy) .to("direct:result"); from("direct:resource") ...
enrich
) retrieves additional data from a resource endpoint in order to enrich an incoming message (contained in the orginal exchange). An aggregation strategy combines the original exchange and the resource exchange. The first parameter of the AggregationStrategy.aggregate(Exchange, Exchange)
method corresponds to the the original exchange, and the second parameter corresponds to the resource exchange. The results from the resource endpoint are stored in the resource exchange's Out message. Here is a sample template for implementing your own aggregation strategy class:
public class ExampleAggregationStrategy implements AggregationStrategy { public Exchange aggregate(Exchange original, Exchange resource) { Object originalBody = original.getIn().getBody(); Object resourceResponse = resource.getOut().getBody(); Object mergeResult = ... // combine original body and resource response if (original.getPattern().isOutCapable()) { original.getOut().setBody(mergeResult); } else { original.getIn().setBody(mergeResult); } return original; } }
Spring XML enrich example
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <enrich uri="direct:resource" strategyRef="aggregationStrategy"/> <to uri="direct:result"/> </route> <route> <from uri="direct:resource"/> ... </route> </camelContext> <bean id="aggregationStrategy" class="..." />
Default aggregation strategy
from("direct:start") .enrich("direct:resource") .to("direct:result");
direct:result
endpoint contains the output from the direct:resource
, because this example does not use any custom aggregation.
strategyRef
attribute, as follows:
<route> <from uri="direct:start"/> <enrich uri="direct:resource"/> <to uri="direct:result"/> </route>
Enrich Options
enrich
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
uri
|
The endpoint uri for the external servie to enrich from. You must use either uri or ref .
|
|
ref
|
Refers to the endpoint for the external servie to enrich from. You must use either uri or ref .
|
|
strategyRef
|
Refers to an AggregationStrategy to be used to merge the reply from the external service, into a single outgoing message. By default Camel will use the reply from the external service as outgoing message. | |
aggregateOnException
|
Refers to the Aggregate method. The aggregateOnException enables you to deal with exceptions. For example, you can suppress the exception or set a custom message. |
Content enrich using pollEnrich
pollEnrich
command treats the resource endpoint as a consumer. Instead of sending an exchange to the resource endpoint, it polls the endpoint. By default, the poll returns immediately, if there is no exchange available from the resource endpoint. For example, the following route reads a file whose name is extracted from the header of an incoming JMS message:
from("activemq:queue:order") .pollEnrich("file://order/data/additional?fileName=orderId") .to("bean:processOrder");
from("activemq:queue:order") .pollEnrich("file://order/data/additional?fileName=orderId", 20000) // timeout is in milliseconds .to("bean:processOrder");
pollEnrich
, as follows:
.pollEnrich("file://order/data/additional?fileName=orderId", 20000, aggregationStrategy)
aggregate()
method might be null
, if the poll times out before an exchange is received.
pollEnrich
does not access any data from the current Exchange, so that, when polling, it cannot use any of the existing headers you may have set on the Exchange. For example, you cannot set a filename in the Exchange.FILE_NAME
header and use pollEnrich
to consume only that file. For that, you must set the filename in the endpoint URI.
Polling methods used by pollEnrich()
pollEnrich()
enricher polls the consumer endpoint using one of the following polling methods:
receiveNoWait()
(used by default)receive()
receive(long timeout)
pollEnrich()
command's timeout argument (specified in milliseconds) determines which method gets called, as follows:
- Timeout is
0
or not specified,receiveNoWait
is called. - Timeout is negative,
receive
is called. - Otherwise,
receive(timeout)
is called.
pollEnrich example
from("direct:start") .pollEnrich("file:inbox?fileName=data.txt") .to("direct:result");
<route> <from uri="direct:start"/> <pollEnrich uri="file:inbox?fileName=data.txt"/> <to uri="direct:result"/> </route>
<route> <from uri="direct:start"/> <pollEnrich uri="file:inbox?fileName=data.txt" timeout="5000"/> <to uri="direct:result"/> </route>
PollEnrich Options
pollEnrich
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
uri
|
The endpoint uri for the external servie to enrich from. You must use either uri or ref .
|
|
ref
|
Refers to the endpoint for the external servie to enrich from. You must use either uri or ref .
|
|
strategyRef
|
Refers to an AggregationStrategy to be used to merge the reply from the external service, into a single outgoing message. By default Camel will use the reply from the external service as outgoing message. | |
timeout
|
0
|
Timeout in millis to use when polling from the external service. See below for important details about the timeout. |
9.2. Content Filter
Overview
Figure 9.2. Content Filter Pattern
Implementing a content filter
- Message translator—see message translators.
- Processors—see Chapter 43, Implementing a Processor.
XML configuration example
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="activemq:My.Queue"/> <to uri="xslt:classpath:com/acme/content_filter.xsl"/> <to uri="activemq:Another.Queue"/> </route> </camelContext>
Using an XPath filter
<route> <from uri="activemq:Input"/> <setBody><xpath resultType="org.w3c.dom.Document">//foo:bar</xpath></setBody> <to uri="activemq:Output"/> </route>
9.3. Normalizer
Overview
Figure 9.3. Normalizer Pattern
Java DSL example
// we need to normalize two types of incoming messages from("direct:start") .choice() .when().xpath("/employee").to("bean:normalizer?method=employeeToPerson") .when().xpath("/customer").to("bean:normalizer?method=customerToPerson") .end() .to("mock:result");
// Java public class MyNormalizer { public void employeeToPerson(Exchange exchange, @XPath("/employee/name/text()") String name) { exchange.getOut().setBody(createPerson(name)); } public void customerToPerson(Exchange exchange, @XPath("/customer/@name") String name) { exchange.getOut().setBody(createPerson(name)); } private String createPerson(String name) { return "<person name=\"" + name + "\"/>"; } }
XML configuration example
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <choice> <when> <xpath>/employee</xpath> <to uri="bean:normalizer?method=employeeToPerson"/> </when> <when> <xpath>/customer</xpath> <to uri="bean:normalizer?method=customerToPerson"/> </when> </choice> <to uri="mock:result"/> </route> </camelContext> <bean id="normalizer" class="org.apache.camel.processor.MyNormalizer"/>
9.4. Claim Check
Claim Check
Figure 9.4. Claim Check Pattern
Java DSL example
from("direct:start").to("bean:checkLuggage", "mock:testCheckpoint", "bean:dataEnricher", "mock:result");
mock:testCheckpoint
endpoint, which checks that the message body has been removed, the claim check added, and so on.
XML DSL example
<route> <from uri="direct:start"/> <pipeline> <to uri="bean:checkLuggage"/> <to uri="mock:testCheckpoint"/> <to uri="bean:dataEnricher"/> <to uri="mock:result"/> </pipeline> </route>
checkLuggage bean
checkLuggage
bean which is implemented as follows:
public static final class CheckLuggageBean { public void checkLuggage(Exchange exchange, @Body String body, @XPath("/order/@custId") String custId) { // store the message body into the data store, using the custId as the claim check dataStore.put(custId, body); // add the claim check as a header exchange.getIn().setHeader("claimCheck", custId); // remove the body from the message exchange.getIn().setBody(null); } }
custId
as the claim check. In this example, we are using a HashMap
to store the message body; in a real application you would use a database or the file system. The claim check is added as a message header for later use and, finally, we remove the body from the message and pass it down the pipeline.
testCheckpoint endpoint
mock:testCheckpoint
endpoint.
dataEnricher bean
dataEnricher
bean, which is implemented as follows:
public static final class DataEnricherBean { public void addDataBackIn(Exchange exchange, @Header("claimCheck") String claimCheck) { // query the data store using the claim check as the key and add the data // back into the message body exchange.getIn().setBody(dataStore.get(claimCheck)); // remove the message data from the data store dataStore.remove(claimCheck); // remove the claim check header exchange.getIn().removeHeader("claimCheck"); } }
claimCheck
header from the message.
9.5. Sort
Sort
java.util.List
).
Java DSL example
from("file://inbox").sort(body().tokenize("\n")).to("bean:MyServiceBean.processLine");
sort()
:
from("file://inbox").sort(body().tokenize("\n"), new MyReverseComparator()).to("bean:MyServiceBean.processLine");
XML configuration example
<route> <from uri="file://inbox"/> <sort> <simple>body</simple> </sort> <beanRef ref="myServiceBean" method="processLine"/> </route>
<route> <from uri="file://inbox"/> <sort comparatorRef="myReverseComparator"> <simple>body</simple> </sort> <beanRef ref="MyServiceBean" method="processLine"/> </route> <bean id="myReverseComparator" class="com.mycompany.MyReverseComparator"/>
<simple>
, you can supply an expression using any language you like, so long as it returns a list.
Options
sort
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
comparatorRef
|
Refers to a custom java.util.Comparator to use for sorting the message body. Camel will by default use a comparator which does a A..Z sorting.
|
9.6. Validate
Overview
true
, the route continues processing normally; if the predicate evaluates to false
, a PredicateValidationException
is thrown.
Java DSL example
from("jms:queue:incoming") .validate(body(String.class).regex("^\\w{10}\\,\\d{2}\\,\\w{24}$")) .to("bean:MyServiceBean.processLine");
from("jms:queue:incoming") .validate(header("bar").isGreaterThan(100)) .to("bean:MyServiceBean.processLine");
from("jms:queue:incoming") .validate(simple("${in.header.bar} == 100")) .to("bean:MyServiceBean.processLine");
XML DSL example
<route> <from uri="jms:queue:incoming"/> <validate> <simple>${body} regex ^\\w{10}\\,\\d{2}\\,\\w{24}$</simple> </validate> <beanRef ref="myServiceBean" method="processLine"/> </route> <bean id="myServiceBean" class="com.mycompany.MyServiceBean"/>
<route> <from uri="jms:queue:incoming"/> <validate> <simple>${in.header.bar} == 100</simple> </validate> <beanRef ref="myServiceBean" method="processLine"/> </route> <bean id="myServiceBean" class="com.mycompany.MyServiceBean"/>
Chapter 10. Messaging Endpoints
Abstract
10.1. Messaging Mapper
Overview
- The canonical message format used to transmit domain objects should be suitable for consumption by non-object oriented applications.
- The mapper code should be implemented separately from both the domain object code and the messaging infrastructure. Apache Camel helps fulfill this requirement by providing hooks that can be used to insert mapper code into a route.
- The mapper might need to find an effective way of dealing with certain object-oriented concepts such as inheritance, object references, and object trees. The complexity of these issues varies from application to application, but the aim of the mapper implementation must always be to create messages that can be processed effectively by non-object-oriented applications.
Finding objects to map
- Find a registered bean. — For singleton objects and small numbers of objects, you could use the
CamelContext
registry to store references to beans. For example, if a bean instance is instantiated using Spring XML, it is automatically entered into the registry, where the bean is identified by the value of itsid
attribute. - Select objects using the JoSQL language. — If all of the objects you want to access are already instantiated at runtime, you could use the JoSQL language to locate a specific object (or objects). For example, if you have a class,
org.apache.camel.builder.sql.Person
, with aname
bean property and the incoming message has aUserName
header, you could select the object whosename
property equals the value of theUserName
header using the following code:import static org.apache.camel.builder.sql.SqlBuilder.sql; import org.apache.camel.Expression; ... Expression expression = sql("SELECT * FROM org.apache.camel.builder.sql.Person where name = :UserName"); Object value = expression.evaluate(exchange);
Where the syntax,:
HeaderName, is used to substitute the value of a header in a JoSQL expression. - Dynamic — For a more scalable solution, it might be necessary to read object data from a database. In some cases, the existing object-oriented application might already provide a finder object that can load objects from the database. In other cases, you might have to write some custom code to extract objects from a database, and in these cases the JDBC component and the SQL component might be useful.
10.2. Event Driven Consumer
Overview
Figure 10.1. Event Driven Consumer Pattern
10.3. Polling Consumer
Overview
receive()
, receive(long timeout)
, and receiveNoWait()
that return a new exchange object, if one is available from the monitored resource. A polling consumer implementation must provide its own thread pool to perform the polling.
Figure 10.2. Polling Consumer Pattern
Scheduled poll consumer
Quartz component
10.4. Competing Consumers
Overview
Figure 10.3. Competing Consumers Pattern
JMS based competing consumers
HighVolumeQ
, as follows:
from("jms:HighVolumeQ").to("cxf:bean:replica01"); from("jms:HighVolumeQ").to("cxf:bean:replica02"); from("jms:HighVolumeQ").to("cxf:bean:replica03");
replica01
, replica02
, and replica03
, process messages from the HighVolumeQ
queue in parallel.
concurrentConsumers
, to create a thread pool of competing consumers. For example, the following route creates a pool of three competing threads that pick messages from the specified queue:
from("jms:HighVolumeQ?concurrentConsumers=3").to("cxf:bean:replica01");
concurrentConsumers
option can also be specified in XML DSL, as follows:
<route> <from uri="jms:HighVolumeQ?concurrentConsumers=3"/> <to uri="cxf:bean:replica01"/> </route>
SEDA based competing consumers
java.util.concurrent.BlockingQueue
). Therefore, you can use a SEDA endpoint to break a route into stages, where each stage might use multiple threads. For example, you can define a SEDA route consisting of two stages, as follows:
// Stage 1: Read messages from file system. from("file://var/messages").to("seda:fanout"); // Stage 2: Perform concurrent processing (3 threads). from("seda:fanout").to("cxf:bean:replica01"); from("seda:fanout").to("cxf:bean:replica02"); from("seda:fanout").to("cxf:bean:replica03");
file://var/messages
, and routes them to a SEDA endpoint, seda:fanout
. The second stage contains three threads: a thread that routes exchanges to cxf:bean:replica01
, a thread that routes exchanges to cxf:bean:replica02
, and a thread that routes exchanges to cxf:bean:replica03
. These three threads compete to take exchange instances from the SEDA endpoint, which is implemented using a blocking queue. Because the blocking queue uses locking to prevent more than one thread from accessing the queue at a time, you are guaranteed that each exchange instance can only be consumed once.
thread()
, see chapter "SEDA" in "Apache Camel Component Reference".
10.5. Message Dispatcher
Overview
Figure 10.4. Message Dispatcher Pattern
JMS selectors
true
, the JMS message is allowed to reach the consumer, and if the selector evaluates to false
, the JMS message is blocked. In many respects, a JMS selector is like a filter processor, but it has the additional advantage that the filtering is implemented inside the JMS provider. This means that a JMS selector can block messages before they are transmitted to the Apache Camel application. This provides a significant efficiency advantage.
selector
query option on a JMS endpoint URI. For example:
from("jms:dispatcher?selector=CountryCode='US'").to("cxf:bean:replica01"); from("jms:dispatcher?selector=CountryCode='IE'").to("cxf:bean:replica02"); from("jms:dispatcher?selector=CountryCode='DE'").to("cxf:bean:replica03");
CountryCode
.
application/x-www-form-urlencoded
MIME format (see the HTML specification). In practice, the &
(ampersand) character might cause difficulties because it is used to delimit each query option in the URI. For more complex selector strings that might need to embed the &
character, you can encode the strings using the java.net.URLEncoder
utility class. For example:
from("jms:dispatcher?selector=" + java.net.URLEncoder.encode("CountryCode='US'","UTF-8")). to("cxf:bean:replica01");
JMS selectors in ActiveMQ
from("activemq:dispatcher?selector=CountryCode='US'").to("cxf:bean:replica01"); from("activemq:dispatcher?selector=CountryCode='IE'").to("cxf:bean:replica02"); from("activemq:dispatcher?selector=CountryCode='DE'").to("cxf:bean:replica03");
Content-based router
10.6. Selective Consumer
Overview
Figure 10.5. Selective Consumer Pattern
JMS selector
true
, the JMS message is allowed to reach the consumer, and if the selector evaluates to false
, the JMS message is blocked. For example, to consume messages from the queue, selective
, and select only those messages whose country code property is equal to US
, you can use the following Java DSL route:
from("jms:selective?selector=" + java.net.URLEncoder.encode("CountryCode='US'","UTF-8")). to("cxf:bean:replica01");
CountryCode='US'
, must be URL encoded (using UTF-8 characters) to avoid trouble with parsing the query options. This example presumes that the JMS property, CountryCode
, is set by the sender. For more details about JMS selectors, see the section called “JMS selectors”.
JMS selector in ActiveMQ
from("acivemq:selective?selector=" + java.net.URLEncoder.encode("CountryCode='US'","UTF-8")). to("cxf:bean:replica01");
Message filter
from("seda:a").filter(header("CountryCode").isEqualTo("US")).process(myProcessor);
<camelContext id="buildCustomProcessorWithFilter" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <filter> <xpath>$CountryCode = 'US'</xpath> <process ref="#myProcessor"/> </filter> </route> </camelContext>
10.7. Durable Subscriber
Overview
- non-durable subscriber—Can have two states: connected and disconnected. While a non-durable subscriber is connected to a topic, it receives all of the topic's messages in real time. However, a non-durable subscriber never receives messages sent to the topic while the subscriber is disconnected.
- durable subscriber—Can have two states: connected and inactive. The inactive state means that the durable subscriber is disconnected from the topic, but wants to receive the messages that arrive in the interim. When the durable subscriber reconnects to the topic, it receives a replay of all the messages sent while it was inactive.
Figure 10.6. Durable Subscriber Pattern
JMS durable subscriber
news
, with a client ID of conn01
and a durable subscription name of John.Doe
:
from("jms:topic:news?clientId=conn01&durableSubscriptionName=John.Doe"). to("cxf:bean:newsprocessor");
from("activemq:topic:news?clientId=conn01&durableSubscriptionName=John.Doe"). to("cxf:bean:newsprocessor");
from("jms:topic:news?clientId=conn01&durableSubscriptionName=John.Doe"). to("seda:fanout"); from("seda:fanout").to("cxf:bean:newsproc01"); from("seda:fanout").to("cxf:bean:newsproc02"); from("seda:fanout").to("cxf:bean:newsproc03");
Alternative example
from("direct:start").to("activemq:topic:foo"); from("activemq:topic:foo?clientId=1&durableSubscriptionName=bar1").to("mock:result1"); from("activemq:topic:foo?clientId=2&durableSubscriptionName=bar2").to("mock:result2");
<route> <from uri="direct:start"/> <to uri="activemq:topic:foo"/> </route> <route> <from uri="activemq:topic:foo?clientId=1&durableSubscriptionName=bar1"/> <to uri="mock:result1"/> </route> <route> <from uri="activemq:topic:foo?clientId=2&durableSubscriptionName=bar2"/> <to uri="mock:result2"/> </route>
from("direct:start").to("activemq:topic:VirtualTopic.foo"); from("activemq:queue:Consumer.1.VirtualTopic.foo").to("mock:result1"); from("activemq:queue:Consumer.2.VirtualTopic.foo").to("mock:result2");
<route> <from uri="direct:start"/> <to uri="activemq:topic:VirtualTopic.foo"/> </route> <route> <from uri="activemq:queue:Consumer.1.VirtualTopic.foo"/> <to uri="mock:result1"/> </route> <route> <from uri="activemq:queue:Consumer.2.VirtualTopic.foo"/> <to uri="mock:result2"/> </route>
10.8. Idempotent Consumer
Overview
MemoryIdempotentRepository
Idempotent consumer with in-memory cache
idempotentConsumer()
processor, which takes two arguments:
messageIdExpression
— An expression that returns a message ID string for the current message.messageIdRepository
— A reference to a message ID repository, which stores the IDs of all the messages received.
TransactionID
header to filter out duplicates.
Example 10.1. Filtering Duplicate Messages with an In-memory Cache
import static org.apache.camel.processor.idempotent.MemoryMessageIdRepository.memoryMessageIdRepository; ... RouteBuilder builder = new RouteBuilder() { public void configure() { from("seda:a") .idempotentConsumer( header("TransactionID"), memoryMessageIdRepository(200) ).to("seda:b"); } };
memoryMessageIdRepository(200)
creates an in-memory cache that can hold up to 200 message IDs.
<camelContext id="buildIdempotentConsumer" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="seda:a"/> <idempotentConsumer messageIdRepositoryRef="MsgIDRepos"> <simple>header.TransactionID</simple> <to uri="seda:b"/> </idempotentConsumer> </route> </camelContext> <bean id="MsgIDRepos" class="org.apache.camel.processor.idempotent.MemoryMessageIdRepository"> <!-- Specify the in-memory cache size. --> <constructor-arg type="int" value="200"/> </bean>
Idempotent consumer with JPA repository
import org.springframework.orm.jpa.JpaTemplate; import org.apache.camel.spring.SpringRouteBuilder; import static org.apache.camel.processor.idempotent.jpa.JpaMessageIdRepository.jpaMessageIdRepository; ... RouteBuilder builder = new SpringRouteBuilder() { public void configure() { from("seda:a").idempotentConsumer( header("TransactionID"), jpaMessageIdRepository(bean(JpaTemplate.class), "myProcessorName") ).to("seda:b"); } };
JpaTemplate
instance—Provides the handle for the JPA database.- processor name—Identifies the current idempotent consumer processor.
SpringRouteBuilder.bean()
method is a shortcut that references a bean defined in the Spring XML file. The JpaTemplate
bean provides a handle to the underlying JPA database. See the JPA documentation for details of how to configure this bean.
Spring XML example
myMessageId
header to filter out duplicates:
<!-- repository for the idempotent consumer --> <bean id="myRepo" class="org.apache.camel.processor.idempotent.MemoryIdempotentRepository"/> <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <idempotentConsumer messageIdRepositoryRef="myRepo"> <!-- use the messageId header as key for identifying duplicate messages --> <header>messageId</header> <!-- if not a duplicate send it to this mock endpoint --> <to uri="mock:result"/> </idempotentConsumer> </route> </camelContext>
Idempotent consumer with JDBC repository
camel-sql
artifact.
SingleConnectionDataSource
JDBC wrapper class from the Spring persistence API in order to instantiate the connection to a SQL database. For example, to instantiate a JDBC connection to a HyperSQL database instance, you could define the following JDBC data source:
<bean id="dataSource" class="org.springframework.jdbc.datasource.SingleConnectionDataSource"> <property name="driverClassName" value="org.hsqldb.jdbcDriver"/> <property name="url" value="jdbc:hsqldb:mem:camel_jdbc"/> <property name="username" value="sa"/> <property name="password" value=""/> </bean>
mem
protocol, which creates a memory-only database instance. This is a toy implementation of the HyperSQL database which is not actually persistent.
<bean id="messageIdRepository" class="org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository"> <constructor-arg ref="dataSource" /> <constructor-arg value="myProcessorName" /> </bean> <camel:camelContext> <camel:errorHandler id="deadLetterChannel" type="DeadLetterChannel" deadLetterUri="mock:error"> <camel:redeliveryPolicy maximumRedeliveries="0" maximumRedeliveryDelay="0" logStackTrace="false" /> </camel:errorHandler> <camel:route id="JdbcMessageIdRepositoryTest" errorHandlerRef="deadLetterChannel"> <camel:from uri="direct:start" /> <camel:idempotentConsumer messageIdRepositoryRef="messageIdRepository"> <camel:header>messageId</camel:header> <camel:to uri="mock:result" /> </camel:idempotentConsumer> </camel:route> </camel:camelContext>
How to handle duplicate messages in the route
skipDuplicate
option to false
which instructs the idempotent consumer to route duplicate messages as well. However the duplicate message has been marked as duplicate by having a property on the Exchange set to true. We can leverage this fact by using a Content-Based Router or Message Filter to detect this and handle duplicate messages.
from("direct:start") // instruct idempotent consumer to not skip duplicates as we will filter then our self .idempotentConsumer(header("messageId")).messageIdRepository(repo).skipDuplicate(false) .filter(property(Exchange.DUPLICATE_MESSAGE).isEqualTo(true)) // filter out duplicate messages by sending them to someplace else and then stop .to("mock:duplicate") .stop() .end() // and here we process only new messages (no duplicates) .to("mock:result");
<!-- idempotent repository, just use a memory based for testing --> <bean id="myRepo" class="org.apache.camel.processor.idempotent.MemoryIdempotentRepository"/> <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <!-- we do not want to skip any duplicate messages --> <idempotentConsumer messageIdRepositoryRef="myRepo" skipDuplicate="false"> <!-- use the messageId header as key for identifying duplicate messages --> <header>messageId</header> <!-- we will to handle duplicate messages using a filter --> <filter> <!-- the filter will only react on duplicate messages, if this property is set on the Exchange --> <property>CamelDuplicateMessage</property> <!-- and send the message to this mock, due its part of an unit test --> <!-- but you can of course do anything as its part of the route --> <to uri="mock:duplicate"/> <!-- and then stop --> <stop/> </filter> <!-- here we route only new messages --> <to uri="mock:result"/> </idempotentConsumer> </route> </camelContext>
How to handle duplicate message in a clustered environment with a data grid
HazelcastIdempotentRepository idempotentRepo = new HazelcastIdempotentRepository("myrepo"); from("direct:in").idempotentConsumer(header("messageId"), idempotentRepo).to("mock:out");
Options
Option | Default | Description |
---|---|---|
eager
|
true
|
Camel 2.0: Eager controls whether Camel adds the message to the repository before or after the exchange has been processed. If enabled before then Camel will be able to detect duplicate messages even when messages are currently in progress. By disabling Camel will only detect duplicates when a message has successfully been processed. |
messageIdRepositoryRef
|
null
|
A reference to a IdempotentRepository to lookup in the registry. This option is mandatory when using XML DSL.
|
skipDuplicate
|
true
|
Camel 2.8: Sets whether to skip duplicate messages. If set to false then the message will be continued. However the Exchange has been marked as a duplicate by having the Exchange.DUPLICATE_MESSAG exchange property set to a Boolean.TRUE value.
|
10.9. Transactional Client
Overview
Figure 10.7. Transactional Client Pattern
Transaction oriented endpoints
CamelContext
. This entails writing code to initialize your transactional components explicitly.
References
10.10. Messaging Gateway
Overview
Figure 10.8. Messaging Gateway Pattern
10.11. Service Activator
Overview
Figure 10.9. Service Activator Pattern
Bean integration
bean()
and beanRef()
that you can insert into a route to invoke methods on a registered Java bean. The detailed mapping of message data to Java method parameters is determined by the bean binding, which can be implemented by adding annotations to the bean class.
BankBean.getUserAccBalance()
, to service requests incoming on a JMS/ActiveMQ queue:
from("activemq:BalanceQueries") .setProperty("userid", xpath("/Account/BalanceQuery/UserID").stringResult()) .beanRef("bankBean", "getUserAccBalance") .to("velocity:file:src/scripts/acc_balance.vm") .to("activemq:BalanceResults");
activemq:BalanceQueries
, have a simple XML format that provides the user ID of a bank account. For example:
<?xml version='1.0' encoding='UTF-8'?> <Account> <BalanceQuery> <UserID>James.Strachan</UserID> </BalanceQuery> </Account>
setProperty()
, extracts the user ID from the In message and stores it in the userid
exchange property. This is preferable to storing it in a header, because the In headers are not available after invoking the bean.
beanRef()
processor, which binds the incoming message to the getUserAccBalance()
method on the Java object identified by the bankBean
bean ID. The following code shows a sample implementation of the BankBean
class:
package tutorial; import org.apache.camel.language.XPath; public class BankBean { public int getUserAccBalance(@XPath("/Account/BalanceQuery/UserID") String user) { if (user.equals("James.Strachan")) { return 1200; } else { return 0; } } }
@XPath
annotation, which injects the content of the UserID
XML element into the user
method parameter. On completion of the call, the return value is inserted into the body of the Out message which is then copied into the In message for the next step in the route. In order for the bean to be accessible to the beanRef()
processor, you must instantiate an instance in Spring XML. For example, you can add the following lines to the META-INF/spring/camel-context.xml
configuration file to instantiate the bean:
<?xml version="1.0" encoding="UTF-8"?> <beans ... > ... <bean id="bankBean" class="tutorial.BankBean"/> </beans>
bankBean
, identifes this bean instance in the registry.
velocity:file:src/scripts/acc_balance.vm
, specifies the location of a velocity script with the following contents:
<?xml version='1.0' encoding='UTF-8'?> <Account> <BalanceResult> <UserID>${exchange.getProperty("userid")}</UserID> <Balance>${body}</Balance> </BalanceResult> </Account>
exchange
, which enables you to retrieve the userid
exchange property, using ${exchange.getProperty("userid")}
. The body of the current In message, ${body}
, contains the result of the getUserAccBalance()
method invocation.
Chapter 11. System Management
Abstract
11.1. Detour
Detour
Example
from("direct:start").to("mock:result")
with a conditional detour to the mock:detour
endpoint in the middle of the route..
from("direct:start").choice() .when().method("controlBean", "isDetour").to("mock:detour").end() .to("mock:result");
<route> <from uri="direct:start"/> <choice> <when> <method bean="controlBean" method="isDetour"/> <to uri="mock:detour"/> </when> </choice> <to uri="mock:result"/> </split> </route>
ControlBean
. So, when the detour is on the message is routed to mock:detour
and then mock:result
. When the detour is off, the message is routed to mock:result
.
11.2. LogEIP
Overview
log
DSL is much lighter and meant for logging human logs such as Starting to do ...
. It can only log a message based on the Simple language. In contrast, the Log component is a fully featured logging component. The Log component is capable of logging the message itself and you have many URI options to control the logging.
Java DSL example
log
DSL command to construct a log message at run time using the Simple expression language. For example, you can create a log message within a route, as follows:
from("direct:start").log("Processing ${id}").to("bean:foo");
String
format message at run time. The log message will by logged at INFO
level, using the route ID as the log name. By default, routes are named consecutively, route-1
, route-2
and so on. But you can use the DSL command, routeId("myCoolRoute")
, to specify a custom route ID.
LoggingLevel.DEBUG
, you can invoke the log DSL as follows:
from("direct:start").log(LoggingLevel.DEBUG, "Processing ${id}").to("bean:foo");
fileRoute
, you can invoke the log DSL as follows:
from("file://target/files").log(LoggingLevel.DEBUG, "fileRoute", "Processing file ${file:name}").to("bean:foo");
XML DSL example
log
element and the log message is specified by setting the message
attribute to a Simple expression, as follows:
<route id="foo"> <from uri="direct:foo"/> <log message="Got ${body}"/> <to uri="mock:foo"/> </route>
log
element supports the message
, loggingLevel
and logName
attributes. For example:
<route id="baz"> <from uri="direct:baz"/> <log message="Me Got ${body}" loggingLevel="FATAL" logName="cool"/> <to uri="mock:baz"/> </route>
11.3. Wire Tap
Wire Tap
Figure 11.1. Wire Tap Pattern
WireTap node
wireTap
node for doing wire taps. The wireTap
node copies the original exchange to a tapped exchange, whose exchange pattern is set to InOnly, because the tapped exchange should be propagated in a oneway style. The tapped exchange is processed in a separate thread, so that it can run concurrently with the main route.
wireTap
supports two different approaches to tapping an exchange:
- Tap a copy of the original exchange.
- Tap a new exchange instance, enabling you to customize the tapped exchange.
Tap a copy of the original exchange
from("direct:start") .to("log:foo") .wireTap("direct:tap") .to("mock:result");
<route> <from uri="direct:start"/> <to uri="log:foo"/> <wireTap uri="direct:tap"/> <to uri="mock:result"/> </route>
Tap and modify a copy of the original exchange
from("direct:start") .wireTap("direct:foo", new Processor() { public void process(Exchange exchange) throws Exception { exchange.getIn().setHeader("foo", "bar"); } }).to("mock:result"); from("direct:foo").to("mock:foo");
from("direct:start") .wireTap("direct:foo", constant("Bye World")) .to("mock:result"); from("direct:foo").to("mock:foo");
processorRef
attribute references a spring bean with the myProcessor
ID:
<route> <from uri="direct:start2"/> <wireTap uri="direct:foo" processorRef="myProcessor"/> <to uri="mock:result"/> </route>
<route> <from uri="direct:start"/> <wireTap uri="direct:foo"> <body><constant>Bye World</constant></body> </wireTap> <to uri="mock:result"/> </route>
Tap a new exchange instance
false
(the default is true
). In this case, an initially empty exchange is created for the wiretap.
from("direct:start") .wireTap("direct:foo", false, new Processor() { public void process(Exchange exchange) throws Exception { exchange.getIn().setBody("Bye World"); exchange.getIn().setHeader("foo", "bar"); } }).to("mock:result"); from("direct:foo").to("mock:foo");
wireTap
argument sets the copy flag to false
, indicating that the original exchange is not copied and an empty exchange is created instead.
from("direct:start") .wireTap("direct:foo", false, constant("Bye World")) .to("mock:result"); from("direct:foo").to("mock:foo");
wireTap
element's copy
attribute to false
.
processorRef
attribute references a spring bean with the myProcessor
ID, as follows:
<route> <from uri="direct:start2"/> <wireTap uri="direct:foo" processorRef="myProcessor" copy="false"/> <to uri="mock:result"/> </route>
<route> <from uri="direct:start"/> <wireTap uri="direct:foo" copy="false"> <body><constant>Bye World</constant></body> </wireTap> <to uri="mock:result"/> </route>
Sending a new Exchange and set headers in DSL
- "Bye World" as message body
- a header with key "id" with the value 123
- a header with key "date" which has current date as value
Java DSL
from("direct:start") // tap a new message and send it to direct:tap // the new message should be Bye World with 2 headers .wireTap("direct:tap") // create the new tap message body and headers .newExchangeBody(constant("Bye World")) .newExchangeHeader("id", constant(123)) .newExchangeHeader("date", simple("${date:now:yyyyMMdd}")) .end() // here we continue routing the original messages .to("mock:result"); // this is the tapped route from("direct:tap") .to("mock:tap");
XML DSL
<route> <from uri="direct:start"/> <!-- tap a new message and send it to direct:tap --> <!-- the new message should be Bye World with 2 headers --> <wireTap uri="direct:tap"> <!-- create the new tap message body and headers --> <body><constant>Bye World</constant></body> <setHeader headerName="id"><constant>123</constant></setHeader> <setHeader headerName="date"><simple>${date:now:yyyyMMdd}</simple></setHeader> </wireTap> <!-- here we continue routing the original message --> <to uri="mock:result"/> </route>
Using onPrepare to execute custom logic when preparing messages
Options
wireTap
DSL command supports the following options:
Name | Default Value | Description |
---|---|---|
uri
|
The endpoint uri where to send the wire tapped message. You should use either uri or ref .
|
|
ref
|
Refers to the endpoint where to send the wire tapped message. You should use either uri or ref .
|
|
executorServiceRef
|
Refers to a custom Thread Pool to be used when processing the wire tapped messages. If not set then Camel uses a default thread pool. | |
processorRef
|
Refers to a custom Processorsto be used for creating a new message (eg the send a new message mode). See below. | |
copy
|
true
|
Camel 2.3: Should a copy of the Exchange to used when wire tapping the message. |
onPrepareRef
|
Camel 2.8: Refers to a custom Processors to prepare the copy of the Exchange to be wire tapped. This allows you to do any custom logic, such as deep-cloning the message payload if that's needed etc. |
1. Service Component Runtime
Abstract
Working with Camel and SCR
org.apache.felix:maven-scr-plugin
. Using SCR, the bundle remains completely in Java world. There is no need to edit XML
or properties file. It offers you full control over the project.
Creating a Service Component
- Add the required
org.apache.felix.scr.annotations
at class level. For example,@Component @References({ @Reference(name = "camelComponent",referenceInterface = ComponentResolver.class, cardinality = ReferenceCardinality.MANDATORY_MULTIPLE, policy = ReferencePolicy.DYNAMIC, policyOption = ReferencePolicyOption.GREEDY, bind = "gotCamelComponent", unbind = "lostCamelComponent") })
- Implement the
getRouteBuilders()
method that returns the Camel route you want to run. For example,@Override protected List<RoutesBuilder> getRouteBuilders() { List<RoutesBuilder> routesBuilders = new ArrayList<>(); routesBuilders.add(new YourRouteBuilderHere(registry)); routesBuilders.add(new AnotherRouteBuilderHere(registry)); return routesBuilders; }
- Finally, enter the default configuration in annotations.
@Properties({ @Property(name = "camelContextId", value = "my-test"), @Property(name = "active", value = "true"), @Property(name = "...", value = "..."), ... })
Example of a Service Component class
camel-archetype-scr
to generate a complete service component class:
// This file was generated from org.apache.camel.archetypes/camel-archetype-scr/2.15-SNAPSHOT package example; import java.util.ArrayList; import java.util.List; import org.apache.camel.scr.AbstractCamelRunner; import example.internal.CamelScrExampleRoute; import org.apache.camel.RoutesBuilder; import org.apache.camel.spi.ComponentResolver; import org.apache.felix.scr.annotations.*; @Component(label = CamelScrExample.COMPONENT_LABEL, description = CamelScrExample.COMPONENT_DESCRIPTION, immediate = true, metatype = true) @Properties({ @Property(name = "camelContextId", value = "camel-scr-example"), @Property(name = "camelRouteId", value = "foo/timer-log"), @Property(name = "active", value = "true"), @Property(name = "from", value = "timer:foo?period=5000"), @Property(name = "to", value = "log:foo?showHeaders=true"), @Property(name = "messageOk", value = "Success: {{from}} -> {{to}}"), @Property(name = "messageError", value = "Failure: {{from}} -> {{to}}"), @Property(name = "maximumRedeliveries", value = "0"), @Property(name = "redeliveryDelay", value = "5000"), @Property(name = "backOffMultiplier", value = "2"), @Property(name = "maximumRedeliveryDelay", value = "60000") }) @References({ @Reference(name = "camelComponent",referenceInterface = ComponentResolver.class, cardinality = ReferenceCardinality.MANDATORY_MULTIPLE, policy = ReferencePolicy.DYNAMIC, policyOption = ReferencePolicyOption.GREEDY, bind = "gotCamelComponent", unbind = "lostCamelComponent") }) public class CamelScrExample extends AbstractCamelRunner { public static final String COMPONENT_LABEL = "example.CamelScrExample"; public static final String COMPONENT_DESCRIPTION = "This is the description for camel-scr-example."; @Override protected List<RoutesBuilder> getRouteBuilders() { List<RoutesBuilder> routesBuilders = new ArrayList<>(); routesBuilders.add(new CamelScrExampleRoute(registry)); return routesBuilders; } }
Example of a RouteBuilder class
camel-archetype-scr
to generate a RouteBuilder
class:
// This file was generated from org.apache.camel.archetypes/camel-archetype-scr/2.15-SNAPSHOT package example.internal; import org.apache.camel.LoggingLevel; import org.apache.camel.builder.RouteBuilder; import org.apache.camel.impl.SimpleRegistry; import org.apache.commons.lang.Validate; public class CamelScrExampleRoute extends RouteBuilder { SimpleRegistry registry; // Configured fields private String camelRouteId; private Integer maximumRedeliveries; private Long redeliveryDelay; private Double backOffMultiplier; private Long maximumRedeliveryDelay; public CamelScrExampleRoute(final SimpleRegistry registry) { this.registry = registry; } @Override public void configure() throws Exception { checkProperties(); // Add a bean to Camel context registry registry.put("test", "bean"); errorHandler(defaultErrorHandler() .retryAttemptedLogLevel(LoggingLevel.WARN) .maximumRedeliveries(maximumRedeliveries) .redeliveryDelay(redeliveryDelay) .backOffMultiplier(backOffMultiplier) .maximumRedeliveryDelay(maximumRedeliveryDelay)); from("{{from}}") .startupOrder(2) .routeId(camelRouteId) .onCompletion() .to("direct:processCompletion") .end() .removeHeaders("CamelHttp*") .to("{{to}}"); from("direct:processCompletion") .startupOrder(1) .routeId(camelRouteId + ".completion") .choice() .when(simple("${exception} == null")) .log("{{messageOk}}") .otherwise() .log(LoggingLevel.ERROR, "{{messageError}}") .end(); } } public void checkProperties() { Validate.notNull(camelRouteId, "camelRouteId property is not set"); Validate.notNull(maximumRedeliveries, "maximumRedeliveries property is not set"); Validate.notNull(redeliveryDelay, "redeliveryDelay property is not set"); Validate.notNull(backOffMultiplier, "backOffMultiplier property is not set"); Validate.notNull(maximumRedeliveryDelay, "maximumRedeliveryDelay property is not set"); } }
Using Apache Camel SCR bundle as a template
- Create a configuration PID for your service component and add a tail with a dash.
- Camel SCR will use the configuration to create a new instance of your component.
- Finally, you can start a new
CamelContext
with your overridden properties.# Create a PID with a tail karaf@root> config:edit example.CamelScrExample-anotherone # Override some properties karaf@root> config:propset camelContextId my-other-context karaf@root> config:propset to "file://removeme?fileName=removemetoo.txt" # Save the PID karaf@root> config:update
NoteMake sure that your service component does not start with the default configuration. To prevent this, addpolicy = ConfigurationPolicy.REQUIRE
to the class level at component annotation.
Using Apache camel-archetype-scr
camel-archetype-scr
and maven, you can easily create Apache Camel SCR bundle project. It includes the following steps:
- Run the following command:
$ mvn archetype:generate -Dfilter=org.apache.camel.archetypes:camel-archetype-scr Choose archetype: local -> org.apache.camel.archetypes:camel-archetype-scr (Creates a new Camel SCR bundle project for Karaf) Choose a number or apply filter (format: [groupId:]artifactId, case sensitive contains): : 1 Define value for property 'groupId': : example [INFO] Using property: groupId = example Define value for property 'artifactId': : camel-scr-example Define value for property 'version': 1.0-SNAPSHOT: : Define value for property 'package': example: : [INFO] Using property: archetypeArtifactId = camel-archetype-scr [INFO] Using property: archetypeGroupId = org.apache.camel.archetypes [INFO] Using property: archetypeVersion = 2.15-SNAPSHOT Define value for property 'className': : CamelScrExample Confirm properties configuration: groupId: example artifactId: camel-scr-example version: 1.0-SNAPSHOT package: example archetypeArtifactId: camel-archetype-scr archetypeGroupId: org.apache.camel.archetypes archetypeVersion: 2.15-SNAPSHOT className: CamelScrExample Y: :
- Run Apache Maven.NoteFor details on setting up Apache Maven to work with Red Hat JBoss Fuse, see Building with Maven in Red Hat JBoss Fuse Deploying into the Container on the Red Hat Customer Portal
- You can now deploy the bundle. To deploy the bundle on Apache Karaf, perform the following steps on Karaf command line:
# Add Camel feature repository karaf@root> features:chooseurl camel 2.15-SNAPSHOT # Install camel-scr feature karaf@root> features:install camel-scr # Install commons-lang, used to validate parameters karaf@root> osgi:install mvn:commons-lang/commons-lang/2.6 # Install and start your bundle karaf@root> osgi:install -s mvn:example/camel-scr-example/1.0-SNAPSHOT # View the log. karaf@root> log:tail -n 10 Press ctrl-c to stop the log.
- By default, the Service Component's configuration PID equals the fully qualified name of its class. You can change the properties of a bundle with Apache Karaf's config.* commands:
# Override the messageOk property karaf@root> config:propset -p example.CamelScrExample messageOk "This is better logging".
You can also change the configuration by editing the property file in Apache Karaf'setc
directory.
Part II. Routing Expression and Predicate Languages
Abstract
Chapter 12. Introduction
Abstract
12.1. Overview of the Languages
Table of expression and predicate languages
Language | Static Method | Fluent DSL Method | XML Element | Annotation | Artifact |
---|---|---|---|---|---|
Section 2.4, “Bean Integration” | bean() | EIP().method() | method | @Bean | Camel core |
Constant | constant() | EIP().constant() | constant | @Constant | Camel core |
EL | el() | EIP().el() | el | @EL | camel-juel |
Groovy | groovy() | EIP().groovy() | groovy | @Groovy | camel-groovy |
Header | header() | EIP().header() | header | @Header | Camel core |
JavaScript | javaScript() | EIP().javaScript() | javaScript | @JavaScript | camel-script |
JoSQL | sql() | EIP().sql() | sql | @SQL | camel-josql |
JSonPath | None | EIP().jsonpath() | jsonpath | @JSonPath | camel-jsonpath |
JXPath | None | EIP().jxpath() | jxpath | @JXPath | camel-jxpath |
MVEL | mvel() | EIP().mvel() | mvel | @MVEL | camel-mvel |
OGNL | ognl() | EIP().ognl() | ognl | @OGNL | camel-ognl |
PHP | php() | EIP().php() | php | @PHP | camel-script |
Property | property() | EIP().property() | property | @Property | Camel core |
Python | python() | EIP().python() | python | @Python | camel-script |
Ref | ref() | EIP().ref() | ref | N/A | Camel core |
Ruby | ruby() | EIP().ruby() | ruby | @Ruby | camel-script |
Simple/File | simple() | EIP().simple() | simple | @Simple | Camel core |
SpEL | spel() | EIP().spel() | spel | @SpEL | camel-spring |
XPath | xpath() | EIP().xpath() | xpath | @XPath | Camel core |
XQuery | xquery() | EIP().xquery() | xquery | @XQuery | camel-saxon |
12.2. How to Invoke an Expression Language
Prerequisites
<dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-script</artifactId> <!-- Use the same version as your Camel core version --> <version>${camel.version}</version> </dependency>
camel-groovy
feature by entering the following OSGi console command:
karaf@root> features:install camel-groovy
Approaches to invoking
As a static method
org.apache.camel.Expression
type or an org.apache.camel.Predicate
type is expected. The static method takes a string expression (or predicate) as its argument and returns an Expression
object (which is usually also a Predicate
object).
/order/address/countryCode
element, as follows:
from("SourceURL") .choice .when(xpath("/order/address/countryCode = 'us'")) .to("file://countries/us/") .when(xpath("/order/address/countryCode = 'uk'")) .to("file://countries/uk/") .otherwise() .to("file://countries/other/") .to("TargetURL");
As a fluent DSL method
filter(xpath("Expression"))
, you can invoke the expression as, filter().xpath("Expression")
.
from("SourceURL") .choice .when().xpath("/order/address/countryCode = 'us'") .to("file://countries/us/") .when().xpath("/order/address/countryCode = 'uk'") .to("file://countries/uk/") .otherwise() .to("file://countries/other/") .to("TargetURL");
As an XML element
xpath
(which belongs to the standard Apache Camel namespace). You can use XPath expressions in a XML DSL content-based router, as follows:
<from uri="file://input/orders"/> <choice> <when> <xpath>/order/address/countryCode = 'us'</xpath> <to uri="file://countries/us/"/> </when> <when> <xpath>/order/address/countryCode = 'uk'</xpath> <to uri="file://countries/uk/"/> </when> <otherwise> <to uri="file://countries/other/"/> </otherwise> </choice>
language
element, where you specify the name of the language in the language
attribute. For example, you can define an XPath expression using the language
element as follows:
<language language="xpath">/order/address/countryCode = 'us'</language>
As an annotation
myBeanProc
, which is invoked as a predicate of the filter()
EIP. If the bean's checkCredentials
method returns true
, the message is allowed to proceed; but if the method returns false
, the message is blocked by the filter. The filter pattern is implemented as follows:
// Java MyBeanProcessor myBeanProc = new MyBeanProcessor(); from("SourceURL") .filter().method(myBeanProc, "checkCredentials") .to("TargetURL");
MyBeanProcessor
class exploits the @XPath
annotation to extract the username
and password
from the underlying XML message, as follows:
// Java import org.apache.camel.language.XPath; public class MyBeanProcessor { boolean void checkCredentials( @XPath("/credentials/username/text()") String user, @XPath("/credentials/password/text()") String pass ) { // Check the user/pass credentials... ... } }
@XPath
annotation is placed just before the parameter into which it gets injected. Notice how the XPath expression explicitly selects the text node, by appending /text()
to the path, which ensures that just the content of the element is selected, not the enclosing tags.
As a Camel endpoint URI
Scheme
), use the following URI syntax:
language://LanguageName:resource:Scheme:Location[?Options]
file:
, classpath:
, or http:
.
mysimplescript.txt
from the classpath:
from("direct:start") .to("language:simple:classpath:org/apache/camel/component/language/mysimplescript.txt") .to("mock:result");
language://LanguageName[:Script][?Options]
script
string:
String script = URLEncoder.encode("Hello ${body}", "UTF-8"); from("direct:start") .to("language:simple:" + script) .to("mock:result");
Chapter 13. Constant
Overview
XML example
username
header to the value, Jane Doe
as follows:
<camelContext> <route> <from uri="SourceURL"/> <setHeader headerName="username"> <constant>Jane Doe</constant> </setHeader> <to uri="TargetURL"/> </route> </camelContext>
Java example
username
header to the value, Jane Doe
as follows:
from("SourceURL") .setHeader("username", constant("Jane Doe")) .to("TargetURL");
Chapter 14. EL
Overview
Adding JUEL package
camel-juel
to your project as shown in Example 14.1, “Adding the camel-juel dependency”.
Example 14.1. Adding the camel-juel dependency
<!-- Maven POM File --> <properties> <camel-version>2.15.1.redhat-620133</camel-version> ... </properties> <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-juel</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Static import
el()
static method in your application code, include the following import statement in your Java source files:
import static org.apache.camel.language.juel.JuelExpression.el;
Variables
Variable | Type | Value |
---|---|---|
exchange | org.apache.camel.Exchange | The current Exchange |
in | org.apache.camel.Message | The IN message |
out | org.apache.camel.Message | The OUT message |
Example
Example 14.2. Routes using EL
<camelContext> <route> <from uri="seda:foo"/> <filter> <language language="el">${in.headers.foo == 'bar'}</language> <to uri="seda:bar"/> </filter> </route> <route> <from uri="seda:foo2"/> <filter> <language language="el">${in.headers['My Header'] == 'bar'}</language> <to uri="seda:bar"/> </filter> </route> </camelContext>
Chapter 15. The File Language
Abstract
15.1. When to Use the File Language
Overview
\
, is not available in the file language.
In a File or FTP consumer endpoint
fileName
, move
, preMove
, moveFailed
, and sortBy
options using a file expression.
fileName
option acts as a filter, determining which file will actually be read from the starting directory. If a plain text string is specified (for example, fileName=report.txt
), the File consumer reads the same file each time it is updated. You can make this option more dynamic, however, by specifying a simple expression. For example, you could use a counter bean to select a different file each time the File consumer polls the starting directory, as follows:
file://target/filelanguage/bean/?fileName=${bean:counter.next}.txt&delete=true
${bean:counter.next}
expression invokes the next()
method on the bean registered under the ID, counter
.
move
option is used to move files to a backup location after then have been read by a File consumer endpoint. For example, the following endpoint moves files to a backup directory, after they have been processed:
file://target/filelanguage/?move=backup/${date:now:yyyyMMdd}/${file:name.noext}.bak&recursive=false
${file:name.noext}.bak
expression modifies the original file name, replacing the file extension with .bak
.
sortBy
option to specify the order in which file should be processed. For example, to process files according to the alphabetical order of their file name, you could use the following File consumer endpoint:
file://target/filelanguage/?sortBy=file:name
file://target/filelanguage/?sortBy=file:modified
reverse:
prefix—for example:
file://target/filelanguage/?sortBy=reverse:file:modified
On exchanges created by a File or FTP consumer
<from uri="file://input/orders"/> <choice> <when> <simple>${file:ext} == 'txt'</simple> <to uri="bean:orderService?method=handleTextFiles"/> </when> <when> <simple>${file:ext} == 'xml'</simple> <to uri="bean:orderService?method=handleXmlFiles"/> </when> <otherwise> <to uri="bean:orderService?method=handleOtherFiles"/> </otherwise> </choice>
15.2. File Variables
Overview
java.io.File
type. The file variables enable you to access various parts of the file pathname, almost as if you were invoking the methods of the java.io.File
class (in fact, the file language extracts the information it needs from message headers that have been set by the File or FTP endpoint).
Starting directory
./filetransfer
(a relative path):
file:filetransfer
./ftptransfer
(a relative path):
ftp://myhost:2100/ftptransfer
Naming convention of file variables
java.io.File
class. For example, the file:absolute
variable gives the value that would be returned by the java.io.File.getAbsolute()
method.
java.io.File.getSize()
.
Table of variables
Variable | Type | Description |
---|---|---|
file:name | String | The pathname relative to the starting directory. |
file:name.ext | String | The file extension (characters following the last . character in the pathname). |
file:name.noext | String | The pathname relative to the starting directory, omitting the file extension. |
file:onlyname | String | The final segment of the pathname. That is, the file name without the parent directory path. |
file:onlyname.noext | String | The final segment of the pathname, omitting the file extension. |
file:ext | String | The file extension (same as file:name.ext ). |
file:parent | String | The pathname of the parent directory, including the starting directory in the path. |
file:path | String | The file pathname, including the starting directory in the path. |
file:absolute | Boolean | true , if the starting directory was specified as an absolute path; false , otherwise. |
file:absolute.path | String | The absolute pathname of the file. |
file:length | Long | The size of the referenced file. |
file:size | Long | Same as file:length . |
file:modified | java.util.Date | Date last modified. |
15.3. Examples
Relative pathname
./filelanguage
:
file://filelanguage
filelanguage
directory, suppose that the endpoint has just consumed the following file:
./filelanguage/test/hello.txt
filelanguage
directory itself has the following absolute location:
/workspace/camel/camel-core/target/filelanguage
Expression | Result |
---|---|
file:name | test/hello.txt |
file:name.ext | txt |
file:name.noext | test/hello |
file:onlyname | hello.txt |
file:onlyname.noext | hello |
file:ext | txt |
file:parent | filelanguage/test |
file:path | filelanguage/test/hello.txt |
file:absolute | false |
file:absolute.path | /workspace/camel/camel-core/target/filelanguage/test/hello.txt |
Absolute pathname
/workspace/camel/camel-core/target/filelanguage
:
file:///workspace/camel/camel-core/target/filelanguage
filelanguage
directory, suppose that the endpoint has just consumed the following file:
./filelanguage/test/hello.txt
Expression | Result |
---|---|
file:name | test/hello.txt |
file:name.ext | txt |
file:name.noext | test/hello |
file:onlyname | hello.txt |
file:onlyname.noext | hello |
file:ext | txt |
file:parent | /workspace/camel/camel-core/target/filelanguage/test |
file:path | /workspace/camel/camel-core/target/filelanguage/test/hello.txt |
file:absolute | true |
file:absolute.path | /workspace/camel/camel-core/target/filelanguage/test/hello.txt |
Chapter 16. Groovy
Overview
camel-script
module.
Adding the script module
camel-script
to your project as shown in Example 16.1, “Adding the camel-script dependency”.
Example 16.1. Adding the camel-script dependency
<!-- Maven POM File --> <properties> <camel-version>2.15.1.redhat-620133</camel-version> ... </properties> <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-script</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Static import
groovy()
static method in your application code, include the following import statement in your Java source files:
import static org.apache.camel.builder.camel.script.ScriptBuilder.*;
Built-in attributes
Attribute | Type | Value |
---|---|---|
context | org.apache.camel.CamelContext | The Camel Context |
exchange | org.apache.camel.Exchange | The current Exchange |
request | org.apache.camel.Message | The IN message |
response | org.apache.camel.Message | The OUT message |
properties | org.apache.camel.builder.script.PropertiesFunction | Function with a resolve method to make it easier to use the properties component inside scripts. |
ENGINE_SCOPE
.
Example
Example 16.2. Routes using Groovy
<camelContext> <route> <from uri="direct:items" /> <filter> <language language="groovy">request.lineItems.any { i -> i.value > 100 }</language> <to uri="mock:mock1" /> </filter> </route> <route> <from uri="direct:in"/> <setHeader headerName="firstName"> <language language="groovy">$user.firstName $user.lastName</language> </setHeader> <to uri="seda:users"/> </route> </camelContext>
Using the properties component
resolve
method on the built-in properties
attribute, as follows:
.setHeader("myHeader").groovy("properties.resolve(PropKey)")
String
type.
Customizing Groovy Shell
GroovyShell
instance, in your Groovy expressions. To provide custom GroovyShell
, add an implementation of the org.apache.camel.language.groovy.GroovyShellFactory SPI
interface to your Camel registry.
GroovyShell
instance that includes the custom static imports, instead of the default one.
public class CustomGroovyShellFactory implements GroovyShellFactory { public GroovyShell createGroovyShell(Exchange exchange) { ImportCustomizer importCustomizer = new ImportCustomizer(); importCustomizer.addStaticStars("com.example.Utils"); CompilerConfiguration configuration = new CompilerConfiguration(); configuration.addCompilationCustomizers(importCustomizer); return new GroovyShell(configuration); } }
Chapter 17. Header
Overview
camel-core
.
XML example
SequenceNumber
header (where the sequence number must be a positive integer), you can define a route as follows:
<camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURL"/> <resequence> <language language="header">SequenceNumber</language> </resequence> <to uri="TargetURL"/> </route> </camelContext>
Java example
from("SourceURL") .resequence(header("SequenceNumber")) .to("TargetURL");
Chapter 18. JavaScript
Overview
camel-script
module.
Adding the script module
camel-script
to your project as shown in Example 18.1, “Adding the camel-script dependency”.
Example 18.1. Adding the camel-script dependency
<!-- Maven POM File --> <properties> <camel-version>2.15.1.redhat-620133</camel-version> ... </properties> <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-script</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Static import
javaScript()
static method in your application code, include the following import statement in your Java source files:
import static org.apache.camel.builder.camel.script.ScriptBuilder.*;
Built-in attributes
Attribute | Type | Value |
---|---|---|
context | org.apache.camel.CamelContext | The Camel Context |
exchange | org.apache.camel.Exchange | The current Exchange |
request | org.apache.camel.Message | The IN message |
response | org.apache.camel.Message | The OUT message |
properties | org.apache.camel.builder.script.PropertiesFunction | Function with a resolve method to make it easier to use the properties component inside scripts. |
ENGINE_SCOPE
.
Example
Example 18.2. Route using JavaScript
<camelContext> <route> <from uri="direct:start"/> <choice> <when> <langauge langauge="javaScript">request.headers.get('user') == 'admin'</langauge> <to uri="seda:adminQueue"/> </when> <otherwise> <to uri="seda:regularQueue"/> </otherwise> </choice> </route> </camelContext>
Using the properties component
resolve
method on the built-in properties
attribute, as follows:
.setHeader("myHeader").javaScript("properties.resolve(PropKey)")
String
type.
Chapter 19. JoSQL
Overview
Adding the JoSQL module
camel-josql
to your project as shown in Example 19.1, “Adding the camel-josql dependency”.
Example 19.1. Adding the camel-josql dependency
<!-- Maven POM File --> ... <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-josql</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Static import
sql()
static method in your application code, include the following import statement in your Java source files:
import static org.apache.camel.builder.sql.SqlBuilder.sql;
Variables
Name | Type | Description |
---|---|---|
exchange | org.apache.camel.Exchange | The current Exchange |
in | org.apache.camel.Message | The IN message |
out | org.apache.camel.Message | The OUT message |
property | Object | the Exchange property whose key is property |
header | Object | the IN message header whose key is header |
variable | Object | the variable whose key is variable |
Example
Example 19.2. Route using JoSQL
<camelContext> <route> <from uri="direct:start"/> <setBody> <language language="sql">select * from MyType</language> </setBody> <to uri="seda:regularQueue"/> </route> </camelContext>
Chapter 20. JSonPath
Overview
jsonpath
DSL command can be used either as an expression or as a predicate (where an empty result gets interpreted as boolean false
).
Adding the JSonPath package
camel-jsonpath
to your project, as follows:
<dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-jsonpath</artifactId> <version>${camel-version}</version> </dependency>
Java example
jsonpath()
DSL command to select items in a certain price range:
from("queue:books.new") .choice() .when().jsonpath("$.store.book[?(@.price < 10)]") .to("jms:queue:book.cheap") .when().jsonpath("$.store.book[?(@.price < 30)]") .to("jms:queue:book.average") .otherwise() .to("jms:queue:book.expensive")
false
. In this way, you can use a JSonPath query as a predicate.
XML example
jsonpath
DSL element to define predicates in a route:
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="direct:start"/> <choice> <when> <jsonpath>$.store.book[?(@.price < 10)]</jsonpath> <to uri="mock:cheap"/> </when> <when> <jsonpath>$.store.book[?(@.price < 30)]</jsonpath> <to uri="mock:average"/> </when> <otherwise> <to uri="mock:expensive"/> </otherwise> </choice> </route> </camelContext>
JSonPath injection
// Java public class Foo { @Consume(uri = "activemq:queue:books.new") public void doSomething(@JsonPath("$.store.book[*].author") String author, @Body String json) { // process the inbound message here } }
Reference
Chapter 21. JXPath
Overview
Adding JXPath package
camel-jxpath
to your project as shown in Example 21.1, “Adding the camel-jxpath dependency”.
Example 21.1. Adding the camel-jxpath dependency
<!-- Maven POM File --> <properties> <camel-version>2.15.1.redhat-620133</camel-version> ... </properties> <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-jxpath</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Variables
Variable | Type | Value |
---|---|---|
this | org.apache.camel.Exchange | The current Exchange |
in | org.apache.camel.Message | The IN message |
out | org.apache.camel.Message | The OUT message |
Example
Example 21.2. Routes using JXPath
<camelContext> <route> <from uri="activemq:MyQueue"/> <filter> <jxpath>in/body/name = 'James'</xpath> <to uri="mqseries:SomeOtherQueue"/> </filter> </route> </camelContext>
Chapter 22. MVEL
Overview
camel-mvel
module.
Syntax
getRequest().getBody().getFamilyName()
Object
type) before invoking the getFamilyName()
method. You can also use an abbreviated syntax for invoking bean attributes, for example:
request.body.familyName
Adding the MVEL module
camel-mvel
to your project as shown in Example 22.1, “Adding the camel-mvel dependency”.
Example 22.1. Adding the camel-mvel dependency
<!-- Maven POM File --> <properties> <camel-version>2.15.1.redhat-620133</camel-version> ... </properties> <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-mvel</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Built-in variables
Name | Type | Description |
---|---|---|
this | org.apache.camel.Exchange | The current Exchange |
exchange | org.apache.camel.Exchange | The current Exchange |
exception | Throwable | the Exchange exception (if any) |
exchangeID | String | the Exchange ID |
fault | org.apache.camel.Message | The Fault message(if any) |
request | org.apache.camel.Message | The IN message |
response | org.apache.camel.Message | The OUT message |
properties | Map | The Exchange properties |
property(name) | Object | The value of the named Exchange property |
property(name, type) | Type | The typed value of the named Exchange property |
Example
Example 22.2. Route using MVEL
<camelContext> <route> <from uri="seda:foo"/> <filter> <language langauge="mvel">request.headers.foo == 'bar'</language> <to uri="seda:bar"/> </filter> </route> </camelContext>
Chapter 23. The Object-Graph Navigation Language(OGNL)
Overview
camel-ognl
module.
Adding the OGNL module
camel-ognl
to your project as shown in Example 23.1, “Adding the camel-ognl dependency”.
Example 23.1. Adding the camel-ognl dependency
<!-- Maven POM File --> ... <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-ognl</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Static import
ognl()
static method in your application code, include the following import statement in your Java source files:
import static org.apache.camel.language.ognl.OgnlExpression.ognl;
Built-in variables
Name | Type | Description |
---|---|---|
this | org.apache.camel.Exchange | The current Exchange |
exchange | org.apache.camel.Exchange | The current Exchange |
exception | Throwable | the Exchange exception (if any) |
exchangeID | String | the Exchange ID |
fault | org.apache.camel.Message | The Fault message(if any) |
request | org.apache.camel.Message | The IN message |
response | org.apache.camel.Message | The OUT message |
properties | Map | The Exchange properties |
property(name) | Object | The value of the named Exchange property |
property(name, type) | Type | The typed value of the named Exchange property |
Example
Example 23.2. Route using OGNL
<camelContext> <route> <from uri="seda:foo"/> <filter> <language langauge="ognl">request.headers.foo == 'bar'</language> <to uri="seda:bar"/> </filter> </route> </camelContext>
Chapter 24. PHP
Overview
camel-script
module.
Adding the script module
camel-script
to your project as shown in Example 24.1, “Adding the camel-script dependency”.
Example 24.1. Adding the camel-script dependency
<!-- Maven POM File --> ... <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-script</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Static import
php()
static method in your application code, include the following import statement in your Java source files:
import static org.apache.camel.builder.camel.script.ScriptBuilder.*;
Built-in attributes
Attribute | Type | Value |
---|---|---|
context | org.apache.camel.CamelContext | The Camel Context |
exchange | org.apache.camel.Exchange | The current Exchange |
request | org.apache.camel.Message | The IN message |
response | org.apache.camel.Message | The OUT message |
properties | org.apache.camel.builder.script.PropertiesFunction | Function with a resolve method to make it easier to use the properties component inside scripts. |
ENGINE_SCOPE
.
Example
Example 24.2. Route using PHP
<camelContext> <route> <from uri="direct:start"/> <choice> <when> <language language="php">strpos(request.headers.get('user'), 'admin')!== FALSE</language> <to uri="seda:adminQueue"/> </when> <otherwise> <to uri="seda:regularQueue"/> </otherwise> </choice> </route> </camelContext>
Using the properties component
resolve
method on the built-in properties
attribute, as follows:
.setHeader("myHeader").php("properties.resolve(PropKey)")
String
type.
Chapter 25. Exchange Property
Overview
camel-core
.
XML example
listOfEndpoints
exchange property contains the recipient list, you could define a route as follows:
<camelContext> <route> <from uri="direct:a"/> <recipientList> <exchangeProperty>listOfEndpoints</exchangeProperty> </recipientList> </route> </camelContext>
Java example
from("direct:a").recipientList(exchangeProperty("listOfEndpoints"));
Chapter 26. Python
Overview
camel-script
module.
Adding the script module
camel-script
to your project as shown in Example 26.1, “Adding the camel-script dependency”.
Example 26.1. Adding the camel-script dependency
<!-- Maven POM File --> ... <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-script</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Static import
python()
static method in your application code, include the following import statement in your Java source files:
import static org.apache.camel.builder.camel.script.ScriptBuilder.*;
Built-in attributes
Attribute | Type | Value |
---|---|---|
context | org.apache.camel.CamelContext | The Camel Context |
exchange | org.apache.camel.Exchange | The current Exchange |
request | org.apache.camel.Message | The IN message |
response | org.apache.camel.Message | The OUT message |
properties | org.apache.camel.builder.script.PropertiesFunction | Function with a resolve method to make it easier to use the properties component inside scripts. |
ENGINE_SCOPE
.
Example
Example 26.2. Route using Python
<camelContext> <route> <from uri="direct:start"/> <choice> <when> <langauge langauge="python">if request.headers.get('user') = 'admin'</langauge> <to uri="seda:adminQueue"/> </when> <otherwise> <to uri="seda:regularQueue"/> </otherwise> </choice> </route> </camelContext>
Using the properties component
resolve
method on the built-in properties
attribute, as follows:
.setHeader("myHeader").python("properties.resolve(PropKey)")
String
type.
Chapter 27. Ref
Overview
camel-core
.
Static import
import static org.apache.camel.language.simple.RefLanguage.ref;
XML example
<beans ...> <bean id="myExpression" class="com.mycompany.MyCustomExpression"/> ... <camelContext> <route> <from uri="seda:a"/> <split> <ref>myExpression</ref> <to uri="mock:b"/> </split> </route> </camelContext> </beans>
Java example
from("seda:a") .split().ref("myExpression") .to("seda:b");
Chapter 28. Ruby
Overview
camel-script
module.
Adding the script module
camel-script
to your project as shown in Example 28.1, “Adding the camel-script dependency”.
Example 28.1. Adding the camel-script dependency
<!-- Maven POM File --> ... <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-script</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Static import
ruby()
static method in your application code, include the following import statement in your Java source files:
import static org.apache.camel.builder.camel.script.ScriptBuilder.*;
Built-in attributes
Attribute | Type | Value |
---|---|---|
context | org.apache.camel.CamelContext | The Camel Context |
exchange | org.apache.camel.Exchange | The current Exchange |
request | org.apache.camel.Message | The IN message |
response | org.apache.camel.Message | The OUT message |
properties | org.apache.camel.builder.script.PropertiesFunction | Function with a resolve method to make it easier to use the properties component inside scripts. |
ENGINE_SCOPE
.
Example
Example 28.2. Route using Ruby
<camelContext> <route> <from uri="direct:start"/> <choice> <when> <langauge langauge="ruby">$request.headers['user'] == 'admin'</langauge> <to uri="seda:adminQueue"/> </when> <otherwise> <to uri="seda:regularQueue"/> </otherwise> </choice> </route> </camelContext>
Using the properties component
resolve
method on the built-in properties
attribute, as follows:
.setHeader("myHeader").ruby("properties.resolve(PropKey)")
String
type.
Chapter 29. The Simple Language
Abstract
29.1. Java DSL
Simple expressions in Java DSL
simple()
command in a route. You can either pass the simple()
command as an argument to a processor, as follows:
from("seda:order") .filter(simple("${in.header.foo}")) .to("mock:fooOrders");
simple()
command as a sub-clause on the processor, for example:
from("seda:order") .filter() .simple("${in.header.foo}") .to("mock:fooOrders");
Embedding in a string
${Expression}
. For example, to embed the in.header.name
expression in a string:
simple("Hello ${in.header.name}, how are you?")
Customizing the start and end tokens
{
and }
, by default) by calling the changeFunctionStartToken
static method and the changeFunctionEndToken
static method on the SimpleLanguage
object.
[
and ]
in Java, as follows:
// Java import org.apache.camel.language.simple.SimpleLanguage; ... SimpleLanguage.changeFunctionStartToken("["); SimpleLanguage.changeFunctionEndToken("]");
camel-core
library on their classpath. For example, in an OSGi server this might affect many applications; whereas in a Web application (WAR file) it would affect only the Web application itself.
29.2. XML DSL
Simple expressions in XML DSL
simple
element. For example, to define a route that performs filtering based on the contents of the foo
header:
<route id="simpleExample"> <from uri="seda:orders"/> <filter> <simple>${in.header.foo}</simple> <to uri="mock:fooOrders"/> </filter> </route>
Alternative placeholder syntax
${Expression}
syntax clashes with another property placeholder syntax. In this case, you can disambiguate the placeholder using the alternative syntax, $simple{Expression}
, for the simple expression. For example:
<simple>Hello $simple{in.header.name}, how are you?</simple>
Customizing the start and end tokens
{
and }
, by default) by overriding the SimpleLanguage
instance. For example, to change the start and end tokens to [
and ]
, define a new SimpleLanguage
bean in your XML configuration file, as follows:
<bean id="simple" class="org.apache.camel.language.simple.SimpleLanguage"> <constructor-arg name="functionStartToken" value="["/> <constructor-arg name="functionEndToken" value="]"/> </bean>
camel-core
library on their classpath. For example, in an OSGi server this might affect many applications; whereas in a Web application (WAR file) it would affect only the Web application itself.
Whitespace and auto-trim in XML DSL
<transform> <simple> data=${body} </simple> </transform>
<transform> <simple>data=${body}</simple> </transform>
<transform> <simple>data=${body}\n</simple> </transform>
trim
attribute to false
, as follows:
<transform trim="false"> <simple>data=${body} </simple> </transform>
29.3. Invoking an External Script
Overview
Syntax for script resource
resource:Scheme:Location
Scheme:
can be either classpath:
, file:
, or http:
.
mysimple.txt
script from the classpath,
simple("resource:classpath:mysimple.txt")
29.4. Expressions
Overview
simple("${header.timeOfDay}")
, would return the contents of a header called timeOfDay
from the incoming message.
${Expression}
, to return a variable value. It is never permissible to omit the enclosing tokens (${
and }
).
Contents of a single variable
in.header.
HeaderName, to obtain the value of the HeaderName header, as follows:
simple("${in.header.foo}")
Variables embedded in a string
simple("Received a message from ${in.header.user} on ${date:in.header.date:yyyyMMdd}.")
date and bean variables
date:
command:
pattern, and for calling bean methods, bean:
beanRef. For example, you can use the date and the bean variables as follows:
simple("Todays date is ${date:now:yyyyMMdd}") simple("The order type is ${bean:orderService?method=getOrderType}")
Specifying the result type
simple()
. For example, to return an integer result, you could evaluate a simple expression as follows:
...
.setHeader("five", simple("5", Integer.class))
resultType
attribute. For example:
<setHeader headerName="five">
<!-- use resultType to indicate that the type should be a java.lang.Integer -->
<simple resultType="java.lang.Integer">5</simple>
</setHeader>
Nested expressions
simple("${header.${bean:headerChooser?method=whichHeader}}")
Accessing constants or enums
type:ClassName.Field
enum
type:
package org.apache.camel.processor; ... public enum Customer { GOLD, SILVER, BRONZE }
Customer
enum fields, as follows:
from("direct:start") .choice() .when().simple("${header.customer} == ${type:org.apache.camel.processor.Customer.GOLD}") .to("mock:gold") .when().simple("${header.customer} == ${type:org.apache.camel.processor.Customer.SILVER}") .to("mock:silver") .otherwise() .to("mock:other");
OGNL expressions
getAddress()
accessor, you can access the Address
object and the Address
object's properties as follows:
simple("${body.address}") simple("${body.address.street}") simple("${body.address.zip}") simple("${body.address.city}")
${body.address.street}
, is shorthand for ${body.getAddress.getStreet}
.
OGNL null-safe operator
?.
, to avoid encountering null-pointer exceptions, in case the body does not have an address. For example:
simple("${body?.address?.street}")
java.util.Map
type, you can look up a value in the map with the key, foo
, using the following notation:
simple("${body[foo]?.name}")
OGNL list element access
[k]
, to access the elements of a list. For example:
simple("${body.address.lines[0]}") simple("${body.address.lines[1]}") simple("${body.address.lines[2]}")
last
keyword returns the index of the last element of a list. For example, you can access the second last element of a list, as follows:
simple("${body.address.lines[last-1]}")
size
method to query the size of a list, as follows:
simple("${body.address.lines.size}")
OGNL array length access
length
method, as follows:
String[] lines = new String[]{"foo", "bar", "cat"}; exchange.getIn().setBody(lines); simple("There are ${body.length} lines")
29.5. Predicates
Overview
simple("${header.timeOfDay} == '14:30'")
, tests whether the timeOfDay
header in the incoming message is equal to 14:30
.
resultType
is specified as a Boolean the expression is evaluated as a predicate instead of an expression. This allows the predicate syntax to be used for these expressions.
Syntax
${LHSVariable} Op RHSValue
- Another variable,
${
RHSVariable}
. - A string literal, enclosed in single quotes,
' '
. - A numeric constant, enclosed in single quotes,
' '
. - The null object,
null
.
Examples
simple("${in.header.user} == 'john'") simple("${in.header.number} > '100'") // String literal can be converted to integer
simple("${in.header.type} in 'gold,silver'")
simple("${in.header.number} regex '\d{4}'")
is
operator, as follows:
simple("${in.header.type} is 'java.lang.String'") simple("${in.header.type} is 'String'") // You can abbreviate java.lang. types
simple("${in.header.number} range '100..199'")
Conjunctions
&&
and ||
.
&&
conjunction (logical and):
simple("${in.header.title} contains 'Camel' && ${in.header.type} == 'gold'")
||
conjunction (logical inclusive or):
simple("${in.header.title} contains 'Camel' || ${in.header.type} == 'gold'")
29.6. Variable Reference
Table of variables
Variable | Type | Description |
---|---|---|
camelContext | Object | The Camel context. Supports OGNL expressions. |
camelId | String | The Camel context's ID value. |
exchangeId | String | The exchange's ID value. |
id | String | The In message ID value. |
body | Object |
The In message body. Supports OGNL expressions.
|
in.body | Object | The In message body. Supports OGNL expressions. |
out.body | Object |
The Out message body.
|
bodyAs(Type) | Type | The In message body, converted to the specified type. All types, Type, must be specified using their fully-qualified Java name, except for the types: byte[] , String , Integer , and Long . The converted body can be null. |
mandatoryBodyAs(Type) | Type | The In message body, converted to the specified type. All types, Type, must be specified using their fully-qualified Java name, except for the types: byte[] , String , Integer , and Long . The converted body is expected to be non-null. |
header. HeaderName | Object |
The In message's HeaderName header. Supports OGNL expressions.
|
header[ HeaderName] | Object |
The In message's HeaderName header (alternative syntax).
|
headers. HeaderName | Object | The In message's HeaderName header. |
headers[ HeaderName] | Object | The In message's HeaderName header (alternative syntax). |
in.header. HeaderName | Object | The In message's HeaderName header. Supports OGNL expressions. |
in.header[ HeaderName] | Object | The In message's HeaderName header (alternative syntax). |
in.headers. HeaderName | Object | The In message's HeaderName header. Supports OGNL expressions. |
in.headers[ HeaderName] | Object | The In message's HeaderName header (alternative syntax). |
out.header. HeaderName | Object |
The Out message's HeaderName header.
|
out.header[ HeaderName] | Object |
The Out message's HeaderName header (alternative syntax).
|
out.headers. HeaderName | Object | The Out message's HeaderName header. |
out.headers[ HeaderName] | Object | The Out message's HeaderName header (alternative syntax). |
headerAs(Key,Type) | Type | The Key header, converted to the specified type. All types, Type, must be specified using their fully-qualified Java name, except for the types: byte[] , String , Integer , and Long . The converted value can be null. |
headers | Map | All of the In headers (as a java.util.Map type). |
in.headers | Map | All of the In headers (as a java.util.Map type). |
property. PropertyName | Object |
The PropertyName property on the exchange.
|
property[ PropertyName] | Object |
The PropertyName property on the exchange (alternative syntax).
|
sys. SysPropertyName | String | The SysPropertyName Java system property. |
sysenv. SysEnvVar | String | The SysEnvVar system environment variable. |
exception | String | Either the exception object from Exchange.getException() or, if this value is null, the caught exception from the Exchange.EXCEPTION_CAUGHT property; otherwise null. Supports OGNL expressions. |
exception.message | String | If an exception is set on the exchange, returns the value of Exception.getMessage() ; otherwise, returns null . |
exception.stacktrace | String | If an exception is set on the exchange, returns the value of Exception.getStackTrace() ; otherwise, returns null . Note: The simple language first tries to retrieve an exception from Exchange.getException() . If that property is not set, it checks for a caught exception, by calling Exchange.getProperty(Exchange.CAUGHT_EXCEPTION) . |
date: command: pattern | String | A date formatted using a java.text.SimpleDateFormat pattern. The following commands are supported: now , for the current date and time; header. HeaderName, or in.header. HeaderName to use a java.util.Date object in the HeaderName header from the In message; out.header. HeaderName to use a java.util.Date object in the HeaderName header from the Out message; |
bean: beanID.Method | Object | Invokes a method on the referenced bean and returns the result of the method invocation. To specify a method name, you can either use the beanID.Method syntax; or you can use the beanID?method= methodName syntax. |
ref: beanID | Object | Looks up the bean with the ID, beanID, in the registry and returns a reference to the bean itself. For example, if you are using the splitter EIP, you could use this variable to reference the bean that implements the splitting algorithm. |
properties:Key | String | The value of the Key property placeholder (see Section 2.7, “Property Placeholders”). |
properties:Location:Key | String | The value of the Key property placeholder, where the location of the properties file is given by Location (see Section 2.7, “Property Placeholders”). |
threadName | String | The name of the current thread. |
routeId | String | Returns the ID of the current route through which the Exchange is being routed. |
type:Name[.Field] | Object | References a type or field by its Fully-Qualified-Name (FQN). To refer to a field, append .Field . For example, you can refer to the FILE_NAME constant field from the Exchange class as type:org.apache.camel.Exchange.FILE_NAME |
29.7. Operator Reference
Binary operators
Operator | Description |
---|---|
== | Equals. |
> | Greater than. |
>= | Greater than or equals. |
< | Less than. |
<= | Less than or equals. |
!= | Not equal to. |
contains | Test if LHS string contains RHS string. |
not contains | Test if LHS string does not contain RHS string. |
regex | Test if LHS string matches RHS regular expression. |
not regex | Test if LHS string does not match RHS regular expression. |
in | Test if LHS string appears in the RHS comma-separated list. |
not in | Test if LHS string does not appear in the RHS comma-separated list. |
is | Test if LHS is an instance of RHS Java type (using Java instanceof operator). |
not is | Test if LHS is not an instance of RHS Java type (using Java instanceof operator). |
range | Test if LHS number lies in the RHS range (where range has the format, ' min... max' ). |
not range | Test if LHS number does not lie in the RHS range (where range has the format, ' min... max' ). |
Unary operators and character escapes
Operator | Description |
---|---|
++ | Increment a number by 1. |
-- | Decrement a number by 1. |
\n | The newline character. |
\r | The carriage return character. |
\t | The tab character. |
\ | (Obsolete) Since Camel version 2.11, the backslash escape character is not supported. |
Combining predicates
Operator | Description |
---|---|
&& | Combine two predicates with logical and. |
|| | Combine two predicates with logical inclusive or. |
and | Deprecated. Use && instead. |
or | Deprecated. Use || instead. |
Chapter 30. SpEL
Overview
Syntax
#{SpelExpression}
, so that they can be embedded in a plain text string (in other words, SpEL has expression templating enabled).
@BeanID
syntax. For example, given a bean with the ID, headerUtils
, and the method, count()
(which counts the number of headers on the current message), you could use the headerUtils
bean in an SpEL predicate, as follows:
#{@headerUtils.count > 4}
Adding SpEL package
camel-spring
to your project as shown in Example 30.1, “Adding the camel-spring dependency”.
Example 30.1. Adding the camel-spring dependency
<!-- Maven POM File --> <properties> <camel-version>2.15.1.redhat-620133</camel-version> ... </properties> <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-spring</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Variables
Variable | Type | Description |
---|---|---|
this | Exchange | The current exchange is the root object. |
exchange | Exchange | The current exchange. |
exchangeId | String | The current exchange's ID. |
exception | Throwable | The exchange exception (if any). |
fault | Message | The fault message (if any). |
request | Message | The exchange's In message. |
response | Message | The exchange's Out message (if any). |
properties | Map | The exchange properties. |
property(Name) | Object | The exchange property keyed by Name. |
property(Name, Type) | Type | The exchange property keyed by Name, converted to the type, Type. |
XML example
Country
header has the value USA
, you can use the following SpEL expression:
<route> <from uri="SourceURL"/> <filter> <spel>#{request.headers['Country'] == 'USA'}}</spel> <to uri="TargetURL"/> </filter> </route>
Java example
from("SourceURL") .filter().spel("#{request.headers['Country'] == 'USA'}") .to("TargetURL");
from("SourceURL") .setBody(spel("Hello #{request.body}! What a beautiful #{request.headers['dayOrNight']}")) .to("TargetURL");
Chapter 31. The XPath Language
Abstract
31.1. Java DSL
Basic expressions
xpath("Expression")
to evaluate an XPath expression on the current exchange (where the XPath expression is applied to the body of the current In message). The result of the xpath()
expression is an XML node (or node set, if more than one node matches).
/person/name
element from the current In message body and use it to set a header named user
, you could define a route like the following:
from("queue:foo") .setHeader("user", xpath("/person/name/text()")) .to("direct:tie");
xpath()
as an argument to setHeader()
, you can use the fluent builder xpath()
command—for example:
from("queue:foo") .setHeader("user").xpath("/person/name/text()") .to("direct:tie");
xpath()
. For example, to specify explicitly that the result type is String
:
xpath("/person/name/text()", String.class)
Namespaces
org.apache.camel.builder.xml.Namespaces
, which enables you to define associations between namespaces and prefixes.
cust
, with the namespace, http://acme.com/customer/record
, and then extract the contents of the element, /cust:person/cust:name
, you could define a route like the following:
import org.apache.camel.builder.xml.Namespaces;
...
Namespaces ns = new Namespaces("cust", "http://acme.com/customer/record");
from("queue:foo")
.setHeader("user", xpath("/cust:person/cust:name/text()", ns))
.to("direct:tie");
xpath()
expression builder by passing the Namespaces
object, ns
, as an additional argument. If you need to define multiple namespaces, use the Namespace.add()
method, as follows:
import org.apache.camel.builder.xml.Namespaces; ... Namespaces ns = new Namespaces("cust", "http://acme.com/customer/record"); ns.add("inv", "http://acme.com/invoice"); ns.add("xsi", "http://www.w3.org/2001/XMLSchema-instance");
xpath()
, as follows:
xpath("/person/name/text()", String.class, ns)
Auditing namespaces
INFO
log level, enable the logNamespaces
option in the Java DSL, as follows:
xpath("/foo:person/@id", String.class).logNamespaces()
TRACE
level logging on the org.apache.camel.builder.xml.XPathBuilder
logger.
2012-01-16 13:23:45,878 [stSaxonWithFlag] INFO XPathBuilder - Namespaces discovered in message: {xmlns:a=[http://apache.org/camel], DEFAULT=[http://apache.org/default], xmlns:b=[http://apache.org/camelA, http://apache.org/camelB]}
31.2. XML DSL
Basic expressions
xpath
element. The XPath expression is applied to the body of the current In message and returns an XML node (or node set). Typically, the returned XML node is automatically converted to a string.
/person/name
element from the current In message body and use it to set a header named user
, you could define a route like the following:
<beans ...> <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="queue:foo"/> <setHeader headerName="user"> <xpath>/person/name/text()</xpath> </setHeader> <to uri="direct:tie"/> </route> </camelContext> </beans>
resultType
attribute to a Java type name (where you must specify the fully-qualified type name). For example, to specify explicitly that the result type is java.lang.String
(you can omit the java.lang.
prefix here):
<xpath resultType="String">/person/name/text()</xpath>
Namespaces
xmlns:Prefix="NamespaceURI"
.
cust
, with the namespace, http://acme.com/customer/record
, and then extract the contents of the element, /cust:person/cust:name
, you could define a route like the following:
<beans ...>
<camelContext xmlns="http://camel.apache.org/schema/spring"
xmlns:cust="http://acme.com/customer/record" >
<route>
<from uri="queue:foo"/>
<setHeader headerName="user">
<xpath>/cust:person/cust:name/text()</xpath>
</setHeader>
<to uri="direct:tie"/>
</route>
</camelContext>
</beans>
Auditing namespaces
INFO
log level, enable the logNamespaces
option in the XML DSL, as follows:
<xpath logNamespaces="true" resultType="String">/foo:person/@id</xpath>
TRACE
level logging on the org.apache.camel.builder.xml.XPathBuilder
logger.
2012-01-16 13:23:45,878 [stSaxonWithFlag] INFO XPathBuilder - Namespaces discovered in message: {xmlns:a=[http://apache.org/camel], DEFAULT=[http://apache.org/default], xmlns:b=[http://apache.org/camelA, http://apache.org/camelB]}
31.3. XPath Injection
Parameter binding annotation
@XPath
annotation to extract a value from the exchange and bind it to a method parameter.
credit
method on an AccountService
object:
from("queue:payments") .beanRef("accountService","credit") ...
credit
method uses parameter binding annotations to extract relevant data from the message body and inject it into its parameters, as follows:
public class AccountService { ... public void credit( @XPath("/transaction/transfer/receiver/text()") String name, @XPath("/transaction/transfer/amount/text()") String amount ) { ... } ... }
Namespaces
XPath
expression that appears in the @XPath
annotation.
Namespace URI | Prefix |
---|---|
http://www.w3.org/2001/XMLSchema | xsd |
http://www.w3.org/2003/05/soap-envelope | soap |
Custom namespaces
@NamespacePrefix
annotation to define custom XML namespaces. Invoke the @NamespacePrefix
annotation to initialize the namespaces
argument of the @XPath
annotation. The namespaces defined by @NamespacePrefix
can then be used in the @XPath
annotation's expression value.
ex
, with the custom namespace, http://fusesource.com/examples
, invoke the @XPath
annotation as follows:
public class AccountService { ... public void credit( @XPath( value = "/ex:transaction/ex:transfer/ex:receiver/text()", namespaces = @NamespacePrefix( prefix = "ex", uri = "http://fusesource.com/examples" ) ) String name, @XPath( value = "/ex:transaction/ex:transfer/ex:amount/text()", namespaces = @NamespacePrefix( prefix = "ex", uri = "http://fusesource.com/examples" ) ) String amount, ) { ... } ... }
31.4. XPath Builder
Overview
org.apache.camel.builder.xml.XPathBuilder
class enables you to evaluate XPath expressions independently of an exchange. That is, if you have an XML fragment from any source, you can use XPathBuilder
to evaluate an XPath expression on the XML fragment.
Matching expressions
matches()
method to check whether one or more XML nodes can be found that match the given XPath expression. The basic syntax for matching an XPath expression using XPathBuilder
is as follows:
boolean matches = XPathBuilder .xpath("Expression") .matches(CamelContext, "XMLString");
true
, because the XPath expression finds a match in the xyz
attribute.
boolean matches = XPathBuilder .xpath("/foo/bar/@xyz") .matches(getContext(), "<foo><bar xyz='cheese'/></foo>"));
Evaluating expressions
evaluate()
method to return the contents of the first node that matches the given XPath expression. The basic syntax for evaluating an XPath expression using XPathBuilder
is as follows:
String nodeValue = XPathBuilder .xpath("Expression") .evaluate(CamelContext, "XMLString");
evaluate()
—for example:
String name = XPathBuilder .xpath("foo/bar") .evaluate(context, "<foo><bar>cheese</bar></foo>", String.class); Integer number = XPathBuilder .xpath("foo/bar") .evaluate(context, "<foo><bar>123</bar></foo>", Integer.class); Boolean bool = XPathBuilder .xpath("foo/bar") .evaluate(context, "<foo><bar>true</bar></foo>", Boolean.class);
31.5. Enabling Saxon
Prerequisites
camel-saxon
artifact (either adding this dependency to your Maven POM, if you use Maven, or adding the camel-saxon-6.2.0.redhat-133.jar
file to your classpath, otherwise).
Using the Saxon parser in Java DSL
saxon()
fluent builder method. For example, you could invoke the Saxon parser as shown in the following example:
// Java // create a builder to evaluate the xpath using saxon XPathBuilder builder = XPathBuilder.xpath("tokenize(/foo/bar, '_')[2]").saxon(); // evaluate as a String result String result = builder.evaluate(context, "<foo><bar>abc_def_ghi</bar></foo>");
Using the Saxon parser in XML DSL
saxon
attribute to true in the xpath
element. For example, you could invoke the Saxon parser as shown in the following example:
<xpath saxon="true" resultType="java.lang.String">current-dateTime()</xpath>
Programming with Saxon
// Java import javax.xml.transform.TransformerFactory; import net.sf.saxon.TransformerFactoryImpl; ... TransformerFactory saxonFactory = new net.sf.saxon.TransformerFactoryImpl();
javax.xml.transform.TransformerFactory
property in the ESBInstall/etc/system.properties
file, as follows:
javax.xml.transform.TransformerFactory=net.sf.saxon.TransformerFactoryImpl
// Java import javax.xml.transform.TransformerFactory; ... TransformerFactory factory = TransformerFactory.newInstance();
net.sf.saxon/saxon9he
(normally installed by default). In versions of Fuse ESB prior to 7.1, it is not possible to load Saxon using the generic JAXP API.
31.6. Expressions
Result type
org.w3c.dom.NodeList
type. You can use the type converter mechanism to convert the result to a different type, however. In the Java DSL, you can specify the result type in the second argument of the xpath()
command. For example, to return the result of an XPath expression as a String
:
xpath("/person/name/text()", String.class)
resultType
attribute, as follows:
<xpath resultType="java.lang.String">/person/name/text()</xpath>
Patterns in location paths
/people/person
- The basic location path specifies the nested location of a particular element. That is, the preceding location path would match the person element in the following XML fragment:
<people> <person>...</person> </people>
Note that this basic pattern can match multiple nodes—for example, if there is more than oneperson
element inside thepeople
element. /name/text()
- If you just want to access the text inside by the element, append
/text()
to the location path, otherwise the node includes the element's start and end tags (and these tags would be included when you convert the node to a string). /person/telephone/@isDayTime
- To select the value of an attribute, AttributeName, use the syntax
@AttributeName
. For example, the preceding location path returnstrue
when applied to the following XML fragment:<person> <telephone isDayTime="true">1234567890</telephone> </person>
*
- A wildcard that matches all elements in the specified scope. For example,
/people/person/*
matches all the child elements ofperson
. @*
- A wildcard that matches all attributes of the matched elements. For example,
/person/name/@*
matches all attributes of every matchedname
element. //
- Match the location path at every nesting level. For example, the
//name
pattern matches everyname
element highlighted in the following XML fragment:<invoice> <person> <name .../> </person> </invoice> <person> <name .../> </person> <name .../>
..
- Selects the parent of the current context node. Not normally useful in the Apache Camel XPath language, because the current context node is the document root, which has no parent.
node()
- Match any kind of node.
text()
- Match a text node.
comment()
- Match a comment node.
processing-instruction()
- Match a processing-instruction node.
Predicate filters
[Predicate]
. For example, you can select the Nth node from the list of matches by appending [N]
to a location path. The following expression selects the first matching person
element:
/people/person[1]
person
element:
/people/person[last()-1]
name
elements, whose surname
attribute is either Strachan or Davies:
/person/name[@surname="Strachan" or @surname="Davies"]
and
, or
, not()
, and you can compare expressions using the comparators, =
, !=
, >
, >=
, <
, <=
(in practice, the less-than symbol must be replaced by the <
entity). You can also use XPath functions in the predicate filter.
Axes
AxisType::MatchingNode
. For example, you can use the child::
axis to search the children of the current context node, as follows:
/invoice/items/child::item
child::item
is the items
element that is selected by the path, /invoice/items
. The child::
axis restricts the search to the children of the context node, items
, so that child::item
matches the children of items
that are named item
. As a matter of fact, the child::
axis is the default axis, so the preceding example can be written equivalently as:
/invoice/items/item
@
is an abbreviation of attribute::
, and //
is an abbreviation of descendant-or-self::
. The full list of axes is as follows (for details consult the reference below):
ancestor
ancestor-or-self
attribute
child
descendant
descendant-or-self
following
following-sibling
namespace
parent
preceding
preceding-sibling
self
Functions
/people/person[last()]
person
element in a sequence (in document order).
Reference
31.7. Predicates
Basic predicates
xpath
in the Java DSL or the XML DSL in a context where a predicate is expected—for example, as the argument to a filter()
processor or as the argument to a when()
clause.
/person/city
element contains the value, London
:
from("direct:tie") .filter().xpath("/person/city = 'London'").to("file:target/messages/uk");
when()
clause:
from("direct:tie") .choice() .when(xpath("/person/city = 'London'")).to("file:target/messages/uk") .otherwise().to("file:target/messages/others");
XPath predicate operators
Operator | Description |
---|---|
= | Equals. |
!= | Not equal to. |
> | Greater than. |
>= | Greater than or equals. |
< | Less than. |
<= | Less than or equals. |
or | Combine two predicates with logical and. |
and | Combine two predicates with logical inclusive or. |
not() | Negate predicate argument. |
31.8. Using Variables and Functions
Evaluating variables in a route
$VarName
or $Prefix:VarName
, if the variable is accessed through an XML namespace.
$in:body
and the In message's header value as $in:HeaderName
. O/S environment variables can be accessed as $env:EnvVar
and Java system properties can be accessed as $system:SysVar
.
/person/city
element and inserts it into the city
header. The second route filters exchanges using the XPath expression, $in:city = 'London'
, where the $in:city
variable is replaced by the value of the city
header.
from("file:src/data?noop=true") .setHeader("city").xpath("/person/city/text()") .to("direct:tie"); from("direct:tie") .filter().xpath("$in:city = 'London'").to("file:target/messages/uk");
Evaluating functions in a route
in:header()
function and the in:body()
function to access a head and the body from the underlying exchange:
from("direct:start").choice() .when().xpath("in:header('foo') = 'bar'").to("mock:x") .when().xpath("in:body() = '<two/>'").to("mock:y") .otherwise().to("mock:z");
in:HeaderName
or in:body
variables. The functions have a slightly different syntax however: in:header('HeaderName')
instead of in:HeaderName
; and in:body()
instead of in:body
.
Evaluating variables in XPathBuilder
XPathBuilder
class. In this case, you cannot use variables such as $in:body
or $in:HeaderName
, because there is no exchange object to evaluate against. But you can use variables that are defined inline using the variable(Name, Value)
fluent builder method.
$test
variable, which is defined to have the value, London
:
String var = XPathBuilder.xpath("$test") .variable("test", "London") .evaluate(getContext(), "<name>foo</name>");
$test
, uses no prefix).
31.9. Variable Namespaces
Table of namespaces
Namespace URI | Prefix | Description |
---|---|---|
http://camel.apache.org/schema/spring | None | Default namespace (associated with variables that have no namespace prefix). |
http://camel.apache.org/xml/in/ | in | Used to reference header or body of the current exchange's In message. |
http://camel.apache.org/xml/out/ | out | Used to reference header or body of the current exchange's Out message. |
http://camel.apache.org/xml/functions/ | functions | Used to reference some custom functions. |
http://camel.apache.org/xml/variables/environment-variables | env | Used to reference O/S environment variables. |
http://camel.apache.org/xml/variables/system-properties | system | Used to reference Java system properties. |
http://camel.apache.org/xml/variables/exchange-property | Undefined | Used to reference exchange properties. You must define your own prefix for this namespace. |
31.10. Function Reference
Table of custom functions
Function | Description |
---|---|
in:body() | Returns the In message body. |
in:header(HeaderName) | Returns the In message header with name, HeaderName. |
out:body() | Returns the Out message body. |
out:header(HeaderName) | Returns the Out message header with name, HeaderName. |
function:properties(PropKey) | Looks up a property with the key, PropKey (see Section 2.7, “Property Placeholders”). |
function:simple(SimpleExp) | Evaluates the specified simple expression, SimpleExp. |
Chapter 32. XQuery
Overview
Java syntax
xquery()
in several ways. For simple expressions, you can pass the XQuery expressions as a string (java.lang.String
). For longer XQuery expressions, you might prefer to store the expression in a file, which you can then reference by passing a java.io.File
argument or a java.net.URL
argument to the overloaded xquery()
method. The XQuery expression implicitly acts on the message content and returns a node set as the result. Depending on the context, the return value is interpreted either as a predicate (where an empty node set is interpreted as false) or as an expression.
Adding the Saxon module
camel-saxon
to your project as shown in Example 32.1, “Adding the camel-saxon dependency”.
Example 32.1. Adding the camel-saxon dependency
<!-- Maven POM File --> ... <dependencies> ... <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-saxon</artifactId> <version>${camel-version}</version> </dependency> ... </dependencies>
Static import
xquery()
static method in your application code, include the following import statement in your Java source files:
import static org.apache.camel.builder.saxon.XQueryBuilder.xquery;
Variables
Variable | Type | Description |
---|---|---|
exchange | Exchange | The current Exchange |
in.body | Object | The body of the IN message |
out.body | Object | The body of the OUT message |
in.headers.key | Object | The IN message header whose key is key |
out.headers.key | Object | The OUT message header whose key is key |
key | Object | The Exchange property whose key is key |
Example
Example 32.2. Route using XQuery
<camelContext> <route> <from uri="activemq:MyQueue"/> <filter> <language langauge="xquery">/foo:person[@name='James']</language> <to uri="mqseries:SomeOtherQueue"/> </filter> </route> </camelContext>
Part III. Web Services and Routing with Camel CXF
Abstract
Chapter 33. Demonstration Code for Camel/CXF
Abstract
33.1. Downloading and Installing the Demonstrations
Overview
Prerequisites
- Java platform—the demonstrations can run on Java 6 or Java 7.
- Apache Maven build tool—to build the demonstration, you require Apache Maven 3.0.4.
- Internet connection—Maven requires an Internet connection in order to download required dependencies from remote repositories while performing a build.
- Red Hat JBoss Fuse—the demonstrations are deployed into the JBoss Fuse container.
Downloading the demonstration package
cxf-webinars-jboss-fuse-6.2.zip
, and is available from the following location:
33.2. Running the Demonstrations
Building the demonstrations
cxf-webinars-jboss-fuse-6.2
, and enter the following commands:
mvn install
cxf-webinars-jboss-fuse-6.2
directory (where the demonstrations are defined to be submodules of the cxf-webinars-jboss-fuse-6.2/pom.xml
project). While Maven is building the demonstration code, it downloads whatever dependencies it needs from the Internet and installs them in the local Maven repository.
Starting and configuring the Red Hat JBoss Fuse container
- (Optional) If your local Maven repository is in a non-standard location, you might need to edit the JBoss Fuse configuration to specify your custom location. Edit the
InstallDir/etc/org.ops4j.pax.url.mvn.cfg
file and set theorg.ops4j.pax.url.mvn.localRepository
property to the location of your local Maven repository:# # Path to the local maven repository which is used to avoid downloading # artifacts when they already exist locally. # The value of this property will be extracted from the settings.xml file # above, or defaulted to: # System.getProperty( "user.home" ) + "/.m2/repository" # #org.ops4j.pax.url.mvn.localRepository= org.ops4j.pax.url.mvn.localRepository=file:E:/Data/.m2/repository
- Launch the JBoss Fuse container. Open a new command prompt, change directory to
InstallDir/bin
, and enter the following command:./fuse
Running the customer-ws-osgi-bundle demonstration
JBossFuse:karaf@root> install -s mvn:com.fusesource.byexample.cxf-webinars/customer-ws-osgi-bundle
JBossFuse:karaf@root> install -s mvn:com.fusesource.byexample.cxf-webinars/customer-ws-client
JBossFuse:karaf@root> log:tail -n 4
2015-08-20 16:10:16,271 | INFO | #0 - timer://foo | timerToLog | ? ? | 198 - org.apache.camel.camel-core - 2.15.1.redhat-620133 | The message contains Hi from Camel at 2015-08-20 16:10:16 2015-08-20 16:10:16,367 | INFO | qtp432302853-183 | CustomerServiceImpl | ? ? | 283 - com.fusesource.byexample.cxf-webinars.customer-ws-osgi-bundle - 1.0.0.SNAPSHOT | Getting status for customer 1234 2015-08-20 16:10:16,370 | INFO | invoker thread. | ClientInvoker | ? ? | 284 - com.fusesource.byexample.cxf-webinars.customer-ws-client - 1.0.0.SNAPSHOT | Got back: status = Active, statusMessage = In the park, playing with my frisbee. 2015-08-20 16:10:18,373 | INFO | qtp432302853-182 | CustomerServiceImpl | ? ? | 283 - com.fusesource.byexample.cxf-webinars.customer-ws-osgi-bundle - 1.0.0.SNAPSHOT | Getting status for customer 1234 2015-08-20 16:10:18,376 | INFO | invoker thread. | ClientInvoker | ? ? | 284 - com.fusesource.byexample.cxf-webinars.customer-ws-client - 1.0.0.SNAPSHOT | Got back: status = Active, statusMessage = In the park, playing with my frisbee.
osgi:list
console command. For example:
JBossFuse:karaf@root> list | grep customer-ws-client [ 284] [Active ] [ ] [Started] [ 80] customer-ws-client (1.0.0.SNAPSHOT)
osgi:stop
console command. For example:
JBossFuse:karaf@root> stop 284
JBossFuse:karaf@root> shutdown -f
Running the other demonstrations
customer-ws-camel-cxf-pojo
customer-ws-camel-cxf-payload
customer-ws-camel-cxf-provider
JBossFuse:karaf@root> features:install camel-cxf JBossFuse:karaf@root> features:install camel-velocity
customer-ws-client
client or using the third-party SoapUI utility.
Chapter 34. Java-First Service Implementation
34.1. Java-First Overview
Overview
Service Endpoint Interface (SEI)
@WebService
annotation.[1]
- Base type of the Web service implementation (server side)—you define the Web service by implementing the SEI.
- Proxy type (client side)—on the client side, you use the SEI to invoke operations on the client proxy object.
- Basis for generating the WSDL contract—in the Java-first approach, you generate the WSDL contract by converting the SEI to WSDL.
WSDL contract
The CustomerService demonstration
CustomerService
Web service using the Java-first approach.
Figure 34.1. Building a Java-First Web Service
Implementing and building the service
- Implement the SEI, which constitutes the basic definition of the Web service's interface.
- Annotate the SEI (you can use the annotations to influence the ultimate form of the generated WSDL contract).
- Implement any other requisite Java classes. In particular, implement the following:
- Any data types referenced by the SEI—for example, the
Customer
class. - The implementation of the SEI,
CustomerServiceImpl
.
- Instantiate the Web service endpoint, by adding the appropriate code to a Spring XML file.
- Generate the WSDL contract using a Java-to-WSDL converter.
34.2. Define SEI and Related Classes
Overview
CustomerService
interface, which enables you to access the details of a customer's account.
The CustomerService SEI
CustomerService
interface, which defines methods for accessing the Customer
data type:
// Java
package com.fusesource.demo.wsdl.customerservice;
// NOT YET ANNOTATED!
public interface CustomerService {
public com.fusesource.demo.customer.Customer lookupCustomer(
java.lang.String customerId
);
public void updateCustomer(
com.fusesource.demo.customer.Customer cust
);
public void getCustomerStatus(
java.lang.String customerId,
javax.xml.ws.Holder<java.lang.String> status,
javax.xml.ws.Holder<java.lang.String> statusMessage
);
}
CustomerService
interface, this interface provides the basis for defining the CustomerService
Web service.
javax.xml.ws.Holder<?> types
getCustomerStatus
method from the CustomerService
interface has parameters declared to be of javax.xml.ws.Holder<String>
type. These so-called holder types are needed in order to declare the OUT
or INOUT
parameters of a WSDL operation.
getStringValues()
, which takes a holder type as its second parameter:
// Java public void getStringValues( String wrongWay, javax.xml.ws.Holder<String> rightWay ) { wrongWay = "Caller will never see this string!"; rightWay.value = "But the caller *can* see this string."; }
rightWay
string as rightWay.value
. For example:
// Java
String wrongWay = "This string never changes";
javax.xml.ws.Holder<String> rightWay.value = "This value *can* change.";
sampleObject.getStringValues(wrongWay, rightWay);
System.out.println("Unchanged string: " + wrongWay);
System.out.println("Changed string: " + rightWay.value);
Holder<>
types in a Java-first example, because this is not a normal Java idiom. But it is interesting to include OUT parameters in the example, so that you can see how a Web service processes this kind of parameter.
Related classes
Default constructor for related classes
The Customer class
Customer
class appears as a related class in the definition of the CustomerService
SEI (the section called “The CustomerService SEI”). The Customer
class consists of a collection of String
fields and the only special condition it needs to satisfy is that it includes a default constructor:
// Java
package com.fusesource.demo.customer;
public class Customer {
protected String firstName;
protected String lastName;
protected String phoneNumber;
protected String id;
// Default constructor, required by JAX-WS
public Customer() { }
public Customer(String firstName, String lastName, String phoneNumber,
String id) {
super();
this.firstName = firstName;
this.lastName = lastName;
this.phoneNumber = phoneNumber;
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String value) {
this.firstName = value;
}
public String getLastName() {
return lastName;
}
public void setLastName(String value) {
this.lastName = value;
}
public String getPhoneNumber() {
return phoneNumber;
}
public void setPhoneNumber(String value) {
this.phoneNumber = value;
}
public String getId() {
return id;
}
public void setId(String value) {
this.id = value;
}
}
34.3. Annotate SEI for JAX-WS
Overview
serviceName
and portName
(there can be more than one implementation of a given SEI).
Minimal annotation
@WebService
. For example, the CustomerService
SEI could be minimally annotated as follows:
// Java package com.fusesource.demo.wsdl.customerservice; import javax.jws.WebService; @WebService public interface CustomerService { ... }
@WebService annotation
@WebService
annotation without any attributes, it is usually better to specify some attributes to provide a more descriptive WSDL service name and WSDL port name. You will also usually want to specify the XML target namespace. For this, you can specify the following optional attributes of the @WebService
annotation:
name
- Specifies the name of the WSDL contract (appearing in the
wsdl:definitions
element). serviceName
- Specifies the name of the WSDL service (a SOAP service is defined by default in the generated contract).
portName
- Specifies the name of the WSDL port (a SOAP/HTTP port is defined by default in the generated contract).
targetNamespace
- The XML schema namespace that is used, by default, to qualify the elements and types defined in the contract.
@WebParam annotation
@WebParam
annotation to method arguments in the SEI. The @WebParam
annotation is optional, but there are a couple of good reasons for adding it:
- By default, JAX-WS maps Java arguments to parameters with names like
arg0
, ...,argN
. Messages are much easier to read, however, when the parameters have meaningful names. - It is a good idea to define parameter elements without a namespace. This makes the XML encoding of requests and responses more compact.
- To enable support for WSDL OUT and INOUT parameters.
@WebParam
annotations with the following attributes:
name
- Specifies the mapped name of the parameter.
targetNamespace
- Specifies the namespace of the mapped parameter. Set this to a blank string for a more compact XML encoding.
mode
- Can have one of the following values:
WebParam.Mode.IN
—(default) parameter is passed from client to service (in request).WebParam.Mode.INOUT
—parameter is passed from client to service (request) and from the service back to the client (in reply).WebParam.Mode.OUT
—parameter is passed from service back to the client (in reply).
OUT and INOUT parameters
- Declare the corresponding Java argument using a
javax.xml.ws.Holder<ParamType>
type, whereParamType
is the type of the parameter you want to send. - Annotate the Java argument with
@WebParam
, setting eithermode = WebParam.Mode.OUT
ormode = WebParam.Mode.INOUT
.
Annotated CustomerService SEI
CustomerService
SEI after it has been annotated. Many other annotations are possible, but this level of annotation is usually adequate for a WSDL-first project.
// Java package com.fusesource.demo.wsdl.customerservice; import javax.jws.WebParam; import javax.jws.WebService; @WebService( targetNamespace = "http://demo.fusesource.com/wsdl/CustomerService/", name = "CustomerService", serviceName = "CustomerService", portName = "SOAPOverHTTP" ) public interface CustomerService { public com.fusesource.demo.customer.Customer lookupCustomer( @WebParam(name = "customerId", targetNamespace = "") java.lang.String customerId ); public void updateCustomer( @WebParam(name = "cust", targetNamespace = "") com.fusesource.demo.customer.Customer cust ); public void getCustomerStatus( @WebParam(name = "customerId", targetNamespace = "") java.lang.String customerId, @WebParam(mode = WebParam.Mode.OUT, name = "status", targetNamespace = "") javax.xml.ws.Holder<java.lang.String> status, @WebParam(mode = WebParam.Mode.OUT, name = "statusMessage", targetNamespace = "") javax.xml.ws.Holder<java.lang.String> statusMessage ); }
34.4. Instantiate the WS Endpoint
Overview
jaxws:endpoint
element in XML. The WS endpoint is effectively the runtime representation of the Web service: it opens an IP port to listen for SOAP/HTTP requests, is responsible for marshalling and unmarshalling messages (making use of the generated Java stub code), and routes incoming requests to the relevant methods on the implementor class.
- Create an instance of the implementor class, using the Spring
bean
element. - Create a WS endpoint, using the
jaxws:endpoint
element.
The jaxws:endpoint element
jaxws:endpoint
element in a Spring file, where the jaxws:
prefix is associated with the http://cxf.apache.org/jaxws
namespace.
jaxws:endpoint
element with the cxf:cxfEndpoint
element, which you meet later in this guide: the jaxws:endpoint
element is used to integrate a WS endpoint with a Java implementation class; whereas the cxf:cxfEndpoint
is used to integrate a WS endpoint with a Camel route.
Define JAX-WS endpoint in XML
jaxws:endpoint
element.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:jaxws="http://cxf.apache.org/jaxws" xmlns:soap="http://cxf.apache.org/bindings/soap" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://cxf.apache.org/bindings/soap http://cxf.apache.org/schemas/configuration/soap.xsd http://cxf.apache.org/jaxws http://cxf.apache.org/schemas/jaxws.xsd"> <jaxws:endpoint xmlns:customer="http://demo.fusesource.com/wsdl/CustomerService/" id="customerService" address="/Customer" serviceName="customer:CustomerService" endpointName="customer:SOAPOverHTTP" implementor="#customerServiceImpl"> </jaxws:endpoint> <bean id="customerServiceImpl" class="com.fusesource.customer.ws.CustomerServiceImpl"/> </beans>
Address for the Jetty container
address
attribute of jaxws:endpoint
is therefore used to configure the addressing information for the endpoint in the Jetty container.
- Address syntax for default servlet container—to use the default servlet container, specify only the servlet context for this endpoint. Do not specify the protocol, host, and IP port in the address. For example, to deploy the endpoint to the
/Customers
servlet context in the default servlet container:address="/Customers"
- Address syntax for custom servlet container—to instantiate a custom Jetty container for the endpoint, specify a complete HTTP URL, including the host and IP port (the value of the IP port effectively identifies the target Jetty container). Typically, for a Jetty container, you specify the host as
0.0.0.0
, which is interpreted as a wildcard that matches every IP network interface on the local machine (that is, if deployed on a multi-homed host, Jetty opens a listening port on every network card). For example, to deploy the endpoint to the custom Jetty container listening on IP port,8083
:address="http://0.0.0.0:8083/Customers"
NoteIf you want to configure a secure endpoint (secured by SSL), you would specify thehttps:
scheme in the address.
Referencing the service implementation
implementor
attribute of the jaxws:endpoint
element references the implementation of the WS service. The value of this attribute can either be the name of the implementation class or (as in this example) a bean reference in the format, #BeanID
, where the #
character indicates that the following identifier is the name of a bean in the bean registry.
34.5. Java-to-WSDL Maven Plug-In
Overview
java2ws
command-line utility or the cxf-java2ws-plugin
Maven plug-in. The plug-in approach is ideal for Maven-based projects: after you paste the requisite plug-in configuration into your POM file, the WSDL code generation step is integrated into your build.
Configure the Java-to-WSDL Maven plug-in
plugin
element into your project's POM file, there are just a few basic settings that need to be customized, as follows:
- CXF version—make sure that the plug-in's dependencies are using the latest version of Apache CXF.
- SEI class name—specify the fully-qualified class name of the SEI in the
configuration/className
element. - Location of output—specify the location of the generated WSDL file in the
configuration/outputFile
element.
cxf-java2ws-plugin
plug-in to generate WSDL from the CustomerService SEI:
<project ...> ... <properties> <cxf.version>3.0.4.redhat-620133</cxf.version> </properties> <build> <defaultGoal>install</defaultGoal> <plugins> ... <plugin> <groupId>org.apache.cxf</groupId> <artifactId>cxf-java2ws-plugin</artifactId> <version>${cxf.version}</version> <dependencies> <dependency> <groupId>org.apache.cxf</groupId> <artifactId>cxf-rt-frontend-jaxws</artifactId> <version>${cxf.version}</version> </dependency> <dependency> <groupId>org.apache.cxf</groupId> <artifactId>cxf-rt-frontend-simple</artifactId> <version>${cxf.version}</version> </dependency> </dependencies> <executions> <execution> <id>process-classes</id> <phase>process-classes</phase> <configuration> <className>org.fusesource.demo.camelcxf.ws.server.CustomerService</className> <outputFile>${basedir}/../src/main/resources/wsdl/CustomerService.wsdl</outputFile> <genWsdl>true</genWsdl> <verbose>true</verbose> </configuration> <goals> <goal>java2ws</goal> </goals> </execution> </executions> </plugin> </plugins> </build> </project>
Generated WSDL
outputFile
configuration element.
outputFile
configuration element, the generated WSDL is sent to the following location, by default:
BaseDir/target/generated/wsdl/SEIClassName.wsdl
Reference
Chapter 35. WSDL-First Service Implementation
35.1. WSDL-First Overview
Overview
Demonstration location
cxf-webinars-jboss-fuse-6.2/customer-ws-osgi-bundle
WSDL contract
Service Endpoint Interface (SEI)
- Base type of the Web service implementation (server side)—you define the Web service by implementing the SEI.
- Proxy type (client side)—on the client side, you use the SEI to invoke operations on the client proxy object.
The CustomerService demonstration
CustomerService
Web service using the WSDL-first approach.
Figure 35.1. Building a WSDL-First Web Service
Implementing and building the service
- Create the WSDL contract.
- Generate the Java stub code from the WSDL contract using a WSDL-to-Java converter,
ws2java
. This gives you the SEI,CustomerService
, and its related classes, such asCustomer
. - Write the implementation of the SEI,
CustomerServiceImpl
. - Instantiate the Web service endpoint, by adding the appropriate code to a Spring XML file.
35.2. CustomerService WSDL Contract
Sample WSDL contract
CustomerService
WSDL contract, which is available in the following location:
cxf-webinars-jboss-fuse-6.2/src/main/resources/wsdl
CustomerSerivice
WSDL contract exposes the following operations:
lookupCustomer
- Given a customer ID, the operation returns the corresponding
Customer
data object. updateCustomer
- Stores the given
Customer
data object against the given customer ID. getCustomerStatus
- Returns the status of the customer with the given customer ID.
Parts of the WSDL contract
Port type
wsdl:portType
element. It is analogous to an interface and it defines the operations that can be invoked on the Web service.
wsdl:portType
definition from the CustomerService
WSDL contract:
<wsdl:definitions name="CustomerService" targetNamespace="http://demo.fusesource.com/wsdl/CustomerService/" ...> ... <wsdl:portType name="CustomerService"> <wsdl:operation name="lookupCustomer"> <wsdl:input message="tns:lookupCustomer"></wsdl:input> <wsdl:output message="tns:lookupCustomerResponse"></wsdl:output> </wsdl:operation> <wsdl:operation name="updateCustomer"> <wsdl:input message="tns:updateCustomer"></wsdl:input> <wsdl:output message="tns:updateCustomerResponse"></wsdl:output> </wsdl:operation> <wsdl:operation name="getCustomerStatus"> <wsdl:input message="tns:getCustomerStatus"></wsdl:input> <wsdl:output message="tns:getCustomerStatusResponse"></wsdl:output> </wsdl:operation> </wsdl:portType> ... </wsdl:definitions>
WSDL binding
WSDL port
CustomerService
WSDL contract defines the following WSDL port:
<wsdl:definitions ...> ... <wsdl:service name="CustomerService"> <wsdl:port name="SOAPOverHTTP" binding="tns:CustomerServiceSOAP"> <soap:address location="http://0.0.0.0:8183/CustomerService" /> </wsdl:port> </wsdl:service> </wsdl:definitions>
soap:address
element's location
attribute in the original WSDL contract is typically overridden at run time, however.
The getCustomerStatus operation
getCustomerStatus
operation has its request parameters (IN parameters) encoded by the getCustomerStatus
element and its response parameters (OUT parameters) encoded by the getCustomerStatusResponse
element, as follows:
<wsdl:definitions name="CustomerService" targetNamespace="http://demo.fusesource.com/wsdl/CustomerService/" ...> <wsdl:types> <xsd:schema ...> ... <xsd:element name="getCustomerStatus"> <xsd:complexType> <xsd:sequence> <xsd:element name="customerId" type="xsd:string"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="getCustomerStatusResponse"> <xsd:complexType> <xsd:sequence> <xsd:element name="status" type="xsd:string"/> <xsd:element name="statusMessage" type="xsd:string"/> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:schema> </wsdl:types> ... </wsdl:definitions>
References
35.3. WSDL-to-Java Maven Plug-In
Overview
ws2java
command-line utility or the cxf-codegen-plugin
Maven plug-in. The plug-in approach is ideal for Maven-based projects: after you paste the requisite plug-in configuration into your POM file, the WSDL-to-Java code generation step is integrated into your build.
Configure the WSDL-to-Java Maven plug-in
plugin
element into your project's POM file, there are just a few basic settings that need to be customized, as follows:
- CXF version—make sure that the plug-in's dependencies are using the latest version of Apache CXF.
- WSDL file location—specify the WSDL file location in the
configuration/wsdlOptions/wsdlOption/wsdl
element. - Location of output—specify the root directory of the generated Java source files in the
configuration/sourceRoot
element.
cxf-codegen-plugin
plug-in to generate Java stub code from the CustomerService.wsdl
WSDL file:
<project ...> ... <parent> <groupId>com.fusesource.byexample.cxf-webinars</groupId> <artifactId>cxf-webinars</artifactId> <version>1.0-SNAPSHOT</version> </parent> <build> <defaultGoal>install</defaultGoal> <plugins> ... <plugin> <groupId>org.apache.cxf</groupId> <artifactId>cxf-codegen-plugin</artifactId> <version>${cxf-version}</version> <executions> <execution> <id>generate-sources</id> <phase>generate-sources</phase> <configuration> <!-- Maven auto-compiles any source files under target/generated-sources/ --> <sourceRoot>${basedir}/target/generated-sources/jaxws</sourceRoot> <wsdlOptions> <wsdlOption> <wsdl>${basedir}/../src/main/resources/wsdl/CustomerService.wsdl</wsdl> </wsdlOption> </wsdlOptions> </configuration> <goals> <goal>wsdl2java</goal> </goals> </execution> </executions> </plugin> </plugins> </build> </project>
Generated Java source code
target/generated-sources/jaxws
directory. Note that the Web service implementation is dependent on this generated stub code—for example, the service implementation class must implement the generated CustomerService
SEI.
Adding the generated source to an IDE
target/generated-sources/jaxws
directory to the project as a source code directory.
Compiling the generated code
BaseDir/target/generated-sources/
Reference
35.4. Instantiate the WS Endpoint
Overview
jaxws:endpoint
element in XML. The WS endpoint is effectively the runtime representation of the Web service: it opens an IP port to listen for SOAP/HTTP requests, is responsible for marshalling and unmarshalling messages (making use of the generated Java stub code), and routes incoming requests to the relevant methods on the implementor class.
- Create an instance of the implementor class, using the Spring
bean
element. - Create a WS endpoint, using the
jaxws:endpoint
element.
Define JAX-WS endpoint in XML
jaxws:endpoint
element.
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jaxws="http://cxf.apache.org/jaxws"
xmlns:soap="http://cxf.apache.org/bindings/soap"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://cxf.apache.org/bindings/soap http://cxf.apache.org/schemas/configuration/soap.xsd
http://cxf.apache.org/jaxws http://cxf.apache.org/schemas/jaxws.xsd">
<jaxws:endpoint
xmlns:customer="http://demo.fusesource.com/wsdl/CustomerService/"
id="customerService"
address="/Customer"
serviceName="customer:CustomerService"
endpointName="customer:SOAPOverHTTP"
implementor="#customerServiceImpl">
</jaxws:endpoint>
<bean id="customerServiceImpl"
class="com.fusesource.customer.ws.CustomerServiceImpl"/>
</beans>
Address for the Jetty container
address
attribute of the jaxws:endpoint
element specifies the servlet context for this endpoint, relative to the Jetty container in which it is deployed.
Referencing the service implementation
implementor
attribute of the jaxws:endpoint
element is used to reference the implementation of the WS service. The value of this attribute can either be the name of the implementation class or (as in this example) a bean reference in the format, #BeanID
, where the #
character indicates that the following identifier is the name of a bean in the bean registry.
35.5. Deploy to an OSGi Container
Overview
- Bundles are a relatively lightweight deployment option (because dependencies can be shared between deployed bundles).
- OSGi provides sophisticated dependency management, ensuring that only version-consistent dependencies are added to the bundle's classpath.
Using the Maven bundle plug-in
pom.xml
file:
- Change the packaging type to
bundle
(by editing the value of theproject/packaging
element in the POM). - Add the Maven bundle plug-in to your POM file and configure it as appropriate.
Sample bundle plug-in configuration
<?xml version="1.0"?> <project ...> ... <groupId>com.fusesource.byexample.cxf-webinars</groupId> <artifactId>customer-ws-osgi-bundle</artifactId> <name>customer-ws-osgi-bundle</name> <url>http://www.fusesource.com</url> <packaging>bundle</packaging> ... <build> <plugins> ... <plugin> <groupId>org.apache.felix</groupId> <artifactId>maven-bundle-plugin</artifactId> <version>${version.maven-bundle-plugin}</version> <extensions>true</extensions> <configuration> <instructions> <Export-Package> !com.fusesource.customer.ws, !com.fusesource.demo.customer, !com.fusesource.demo.wsdl.customerservice </Export-Package> <Import-Package> * </Import-Package> <DynamicImport-Package> org.apache.cxf.*, org.springframework.beans.* </DynamicImport-Package> </instructions> </configuration> </plugin> ... </plugins> </build> </project>
Dynamic imports
DynamicImport-Package
element). This is a pragmatic way of dealing with the fact that Spring XML files are not terribly well integrated with the Maven bundle plug-in. At build time, the Maven bundle plug-in is not able to figure out which Java classes are required by the Spring XML code. By listing wildcarded package names in the DynamicImport-Package
element, however, you allow the OSGi container to figure out which Java classes are needed by the Spring XML code at run time.
DynamicImport-Package
headers is not recommended in OSGi, because it short-circuits OSGi version checking. Normally, what should happen is that the Maven bundle plug-in lists the Java packages used at build time, along with their versions, in the Import-Package
header. At deploy time, the OSGi container then checks that the available Java packages are compatible with the build-time versions listed in the Import-Package
header. With dynamic imports, this version checking cannot be performed.
Build and deploy the service bundle
mvn install
karaf@root> install -s mvn:com.fusesource.byexample.cxf-webinars/customer-ws-osgi-bundle
org.ops4j.pax.url.mvn.localRepository
property in the EsbInstallDir/etc/org.ops4j.pax.url.mvn.cfg
file, before you can use the mvn:
scheme to access Maven artifacts.
Red Hat JBoss Fuse default servlet container
cxf/
. Hence, any WS endpoint whose address
attribute is configured in the jaxws:endpoint
element as /EndpointContext
will have the following effective address:
http://Hostname:8181/cxf/EndpointContext
InstallDir/etc/org.ops4j.pax.web.cfg
Check that the service is running
http://localhost:8181/cxf/Customer?wsdl
Chapter 36. Implementing a WS Client
36.1. WS Client Overview
Overview
jaxws:client
element in Spring XML.
Demonstration location
cxf-webinars-jboss-fuse-6.2/customer-ws-client
WSDL contract
Service Endpoint Interface (SEI)
WS client proxy
The CustomerService client
customer-ws-client
demonstration, which is available from the following location:
cxf-webinars-jboss-fuse-6.2/customer-ws-client
Figure 36.1. Building a WS Client
Implementing and building the WS client
- Obtain a copy of the WSDL contract.
- Generate the Java stub code from the WSDL contract using a WSDL-to-Java converter,
ws2java
. This gives you the SEI,CustomerService
, and its related classes, such asCustomer
. - Implement the main client class,
ClientInvoker
, which invokes the Web service operations. In this class define a bean property of type,CustomerService
, so that the client class can receive a reference to the WS client proxy by property injection. - In a Spring XML file, instantiate the WS client proxy and inject it into the main client class,
ClientInvoker
.
36.2. WSDL-to-Java Maven Plug-In
Overview
ws2java
command-line utility or the cxf-codegen-plugin
Maven plug-in. When using Maven, the plug-in approach is ideal: after you paste the requisite plug-in configuration into your POM file, the WSDL-to-Java code generation step is integrated into your build.
Configure the WSDL-to-Java Maven plug-in
plugin
element into your project's POM file, there are just a few basic settings that need to be customized, as follows:
- CXF version—make sure that the plug-in's dependencies are using the latest version of Apache CXF.
- WSDL file location—specify the WSDL file location in the
configuration/wsdlOptions/wsdlOption/wsdl
element. - Location of output—specify the root directory of the generated Java source files in the
configuration/sourceRoot
element.
cxf-codegen-plugin
plug-in to generate Java stub code from the CustomerService.wsdl
WSDL file:
<project ...> ... <parent> <groupId>com.fusesource.byexample.cxf-webinars</groupId> <artifactId>cxf-webinars</artifactId> <version>1.0-SNAPSHOT</version> </parent> <build> <defaultGoal>install</defaultGoal> <plugins> ... <plugin> <groupId>org.apache.cxf</groupId> <artifactId>cxf-codegen-plugin</artifactId> <version>${cxf-version}</version> <executions> <execution> <id>generate-sources</id> <phase>generate-sources</phase> <configuration> <sourceRoot>${basedir}/target/generated-sources/jaxws</sourceRoot> <wsdlOptions> <wsdlOption> <wsdl>${basedir}/../src/main/resources/wsdl/CustomerService.wsdl</wsdl> </wsdlOption> </wsdlOptions> </configuration> <goals> <goal>wsdl2java</goal> </goals> </execution> </executions> </plugin> </plugins> </build> </project>
Generated Java source code
target/generated-sources/jaxws
directory. Note that the client implementation is dependent on this generated stub code—for example, the client invokes the proxy using the generated CustomerService
SEI.
Add generated source to IDE
target/generated-sources/jaxws
directory to the project as a source code directory.
Compiling the generated code
BaseDir/target/generated-sources/
Reference
36.3. Instantiate the WS Client Proxy
Overview
jaxws:client
element.
Define the WS client in XML
jaxws:client
element.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:jaxws="http://cxf.apache.org/jaxws" xmlns:soap="http://cxf.apache.org/bindings/soap" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://cxf.apache.org/bindings/soap http://cxf.apache.org/schemas/configuration/soap.xsd http://cxf.apache.org/jaxws http://cxf.apache.org/schemas/jaxws.xsd"> <jaxws:client id="customerServiceProxy" address="http://localhost:8181/cxf/Customer" serviceClass="com.fusesource.demo.wsdl.customerservice.CustomerService" /> <bean id="customerServiceClient" class="com.fusesource.customer.client.ClientInvoker" init-method="init" destroy-method="destroy"> <property name="customerService" ref="customerServiceProxy"/> </bean> </beans>
The jaxws:client element
jaxws:client
element creates a client proxy dynamically (that is, there is no dedicated class that represents a proxy implementation in the Java stub code). The following attributes are used to define the proxy:
-
id
- The ID that you specify here is entered in the bean registry and can be used to reference the proxy instance from other beans.
-
address
- The full address of the remote Web service that this proxy connects to.
-
serviceClass
- The fully-qualified class name of the Web service's SEI (you invoke methods on the proxy through the SEI).
Injecting with the proxy reference
customerServiceProxy
, you can inject it into a bean property using the Spring property
element, as follows:
<bean ...>
<property name="customerService" ref="customerServiceProxy"/>
</bean>
setCustomerService
setter method—for example:
// Java ... public class ClientInvoker implements Runnable { ... public void setCustomerService(CustomerService customerService) { this.customerService = customerService; } }
36.4. Invoke WS Operations
Proxy interface is SEI interface
Invoking the lookupCustomer operation
CustomerService
SEI exposes the lookupCustomer
method, which takes a customer ID as its argument and returns a Customer
data object. Using the proxy instance, customerService
, you can invoke the lookupCustomer
operation as follows:
// Java com.fusesource.demo.customer.Customer response = customerService.lookupCustomer("1234"); log.info("Got back " + response.getFirstName() + " " + response.getLastName() + ", ph:" + response.getPhoneNumber() );
The ClientInvoker class
cxf-webinars-jboss-fuse-6.2/customer-ws-client
project, there is a ClientInvoker
class (located in src/main/java/com/fusesource/customer/client
), which defines a continuous loop that invokes the lookupCustomer
operation.
ClientInvoker
class, possibly adding operation invocations.
36.5. Deploy to an OSGi Container
Overview
- Bundles are a relatively lightweight deployment option (because dependencies can be shared between deployed bundles).
- OSGi provides sophisticated dependency management, ensuring that only version-consistent dependencies are added to the bundle's classpath.
Using the Maven bundle plug-in
pom.xml
file:
- Change the packaging type to
bundle
(by editing the value of theproject/packaging
element in the POM). - Add the Maven bundle plug-in to your POM file and configure it as appropriate.
Sample bundle plug-in configuration
<?xml version="1.0"?> <project ...> ... <groupId>com.fusesource.byexample.cxf-webinars</groupId> <artifactId>customer-ws-client</artifactId> <name>customer-ws-client</name> <packaging>bundle</packaging> ... <build> <plugins> ... <plugin> <groupId>org.apache.felix</groupId> <artifactId>maven-bundle-plugin</artifactId> <extensions>true</extensions> <configuration> <instructions> <Export-Package> !com.fusesource.customer.client, !com.fusesource.demo.customer, !com.fusesource.demo.wsdl.customerservice </Export-Package> <Import-Package> * </Import-Package> <DynamicImport-Package> org.apache.cxf.*, org.springframework.beans.* </DynamicImport-Package> </instructions> </configuration> </plugin> ... </plugins> </build> </project>
Dynamic imports
DynamicImport-Package
element). This is a pragmatic way of dealing with the fact that Spring XML files are not terribly well integrated with the Maven bundle plug-in. At build time, the Maven bundle plug-in is not able to figure out which Java classes are required by the Spring XML code. By listing wildcarded package names in the DynamicImport-Package
element, however, you allow the OSGi container to figure out which Java classes are needed by the Spring XML code at run time.
DynamicImport-Package
headers is not recommended in OSGi, because it short-circuits OSGi version checking. Normally, what should happen is that the Maven bundle plug-in lists the Java packages used at build time, along with their versions, in the Import-Package
header. At deploy time, the OSGi container then checks that the available Java packages are compatible with the build time versions listed in the Import-Package
header. With dynamic imports, this version checking cannot be performed.
Build and deploy the client bundle
mvn install
karaf@root> install -s mvn:com.fusesource.byexample.cxf-webinars/customer-ws-client
org.ops4j.pax.url.mvn.localRepository
property in the EsbInstallDir/etc/org.ops4j.pax.url.mvn.cfg
file, before you can use the mvn:
scheme to access Maven artifacts.
Check that the client is running
karaf@root> log:display -n 10
Chapter 37. Pojo-Based Route
37.1. Processing Messages in POJO Format
Overview
- The big advantage of the POJO data format is that the operation parameters are encoded using the JAXB standard, which makes them easy to manipulate in Java.
- The downside of the POJO data format, on the other hand, is that it requires that the WSDL metadata is converted to Java in advance (as defined by the JAX-WS and JAXB mappings) and compiled into your application. This means that a POJO-based route is not very dynamic.
Demonstration location
cxf-webinars-jboss-fuse-6.2/customer-ws-camel-cxf-pojo
Camel CXF component
cxf:cxfEndpoint
XML element and are implemented by the Apache Camel project—are not to be confused with the Apache CXF JAX-WS endpoints—which are instantiated using the jaxws:endpoint
XML element and are implemented by the Apache CXF project.
POJO data format
- JAX-WS and JAXB stub code (as generated from the WSDL contract) must be provided.
- The SOAP body is marshalled into a list of Java objects.
- One Java object for each part or parameter of the corresponding WSDL operation.
- The type of the message body is
org.apache.cxf.message.MessageContentsList
.
- The SOAP headers are converted into headers in the exchange's In message.
Implementing and building a POJO route
- Obtain a copy of the WSDL contract that is to be integrated into the route.
- Generate the Java stub code from the WSDL contract using a WSDL-to-Java converter. This gives you the SEI,
CustomerService
, and its related classes, such asCustomer
. - Instantiate the Camel CXF endpoint in Spring, using the
cxf:cxfEndpoint
element. - Implement the route in XML, where you can use the content-based router to sort requests by operation name.
- Implement the operation processor beans, which are responsible for processing each operation. When implementing these beans, the message contents must be accessed in POJO data format.
Sample POJO route
CustomerService
Web service using the POJO data format. After sorting the request messages by operation name, an operation-specific processor bean reads the incoming request parameters and then generates a response in the POJO data format.
Figure 37.1. Sample POJO Route
37.2. WSDL-to-Java Maven Plug-In
Overview
ws2java
command-line utility or the cxf-codegen-plugin
Maven plug-in. When using Maven, the plug-in approach is ideal: after you paste the requisite plug-in configuration into your POM file, the WSDL-to-Java code generation step is integrated into your build.
Configure the WSDL-to-Java Maven plug-in
plugin
element into your project's POM file, there are just a few basic settings that need to be customized, as follows:
- CXF version—make sure that the plug-in's dependencies are using the latest version of Apache CXF.
- WSDL file location—specify the WSDL file location in the
configuration/wsdlOptions/wsdlOption/wsdl
element. - Location of output—specify the root directory of the generated Java source files in the
configuration/sourceRoot
element.
cxf-codegen-plugin
plug-in to generate Java stub code from the CustomerService.wsdl
WSDL file:
<project ...> ... <parent> <groupId>com.fusesource.byexample.cxf-webinars</groupId> <artifactId>cxf-webinars</artifactId> <version>1.0-SNAPSHOT</version> </parent> <build> <defaultGoal>install</defaultGoal> <plugins> ... <plugin> <groupId>org.apache.cxf</groupId> <artifactId>cxf-codegen-plugin</artifactId> <version>${cxf-version}</version> <executions> <execution> <id>generate-sources</id> <phase>generate-sources</phase> <configuration> <sourceRoot>${basedir}/target/generated-sources/jaxws</sourceRoot> <wsdlOptions> <wsdlOption> <wsdl>${basedir}/../src/main/resources/wsdl/CustomerService.wsdl</wsdl> </wsdlOption> </wsdlOptions> </configuration> <goals> <goal>wsdl2java</goal> </goals> </execution> </executions> </plugin> </plugins> </build> </project>
Generated Java source code
target/generated-sources/jaxws
directory. Note that the route is dependent on this generated stub code—for example, when processing the POJO parameters, the parameter processor uses the Customer
data type from the stub code.
Add generated code to IDE
target/generated-sources/jaxws
directory to the project as a source code directory.
Compiling the generated code
BaseDir/target/generated-sources/
Reference
37.3. Instantiate the WS Endpoint
Overview
- Consumer—(at the start of a route) represents a Web service instance, which integrates with the route. The type of payload injected into the route depends on the value of the endpoint's
dataFormat
option. - Producer—(at other points in the route) represents a WS client proxy, which converts the current exchange object into an operation invocation on a remote Web service. The format of the current exchange must match the endpoint's
dataFormat
setting.
dataFormat
option set to POJO.
Maven dependency
camel-cxf
component in your Maven POM. For example, the pom.xml
file from the customer-ws-camel-cxf-pojo
demonstration project includes the following dependency:
<dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-cxf</artifactId> <version>${camel-version}</version> </dependency>
The cxf:bean: URI syntax
cxf:bean:
URI is used to bind an Apache CXF endpoint to a route and has the following general syntax:
cxf:bean:CxfEndpointID[?Options]
CxfEndpointID
is the ID of a bean created using the cxf:cxfEndpoint
element, which configures the details of the WS endpoint. You can append options to this URI (where the options are described in detail in chapter "CXF" in "Apache Camel Component Reference"). If you do not specify any additional options, the endpoint uses the POJO data format by default.
customer-ws
, define the route as follows:
<route>
<from uri="cxf:bean:customer-ws"/>
...
</route>
cxf://WsAddress[?Options]
, which enables you to specify all of the WS endpoint details in the URI (so there is no need to reference a bean instance). This typically results in a long and cumbersome URI, but is useful in some cases.
The cxf:cxfEndpoint element
cxf:cxfEndpoint
element is used to define a WS endpoint that binds either to the start (consumer endpoint) or the end (producer endpoint) of a route. For example, to define the customer-ws
WS endpoint referenced in the preceding route, you would define a cxf:cxfEndpoint
element as follows:
<?xml version="1.0" encoding="UTF-8"?> <beans ... xmlns:cxf="http://camel.apache.org/schema/cxf" ...> ... <cxf:cxfEndpoint id="customer-ws" address="/Customer" endpointName="c:SOAPOverHTTP" serviceName="c:CustomerService" serviceClass="com.fusesource.demo.wsdl.customerservice.CustomerService" xmlns:c="http://demo.fusesource.com/wsdl/CustomerService/"/> ... </beans>
cxf:cxfEndpoint
element and the jaxws:endpoint
element use different XML schemas (although the syntax looks superficially similar). These elements bind a WS endpoint in different ways: the cxf:cxfEndpoint
element instantiates and binds a WS endpoint to an Apache Camel route, whereas the jaxws:endpoint
element instantiates and binds a WS endpoint to a Java class using the JAX-WS mapping.
Address for the Jetty container
address
attribute of cxf:cxfEndpoint
is therefore used to configure the addressing information for the endpoint in the Jetty container.
- Address syntax for default servlet container—to use the default servlet container, specify only the servlet context for this endpoint. Do not specify the protocol, host, and IP port in the address. For example, to deploy the endpoint to the
/Customer
servlet context in the default servlet container:address="/Customer"
- Address syntax for custom servlet container—to instantiate a custom Jetty container for this endpoint, specify a complete HTTP URL, including the host and IP port (the value of the IP port effectively identifies the target Jetty container). Typically, for a Jetty container, you specify the host as
0.0.0.0
, which is interpreted as a wildcard that matches every IP network interface on the local machine (that is, if deployed on a multi-homed host, Jetty opens a listening port on every network card). For example, to deploy the endpoint to the custom Jetty container listening on IP port,8083
:address="http://0.0.0.0:8083/Customer"
NoteIf you want to configure a secure endpoint (secured by SSL), you would specify thehttps:
scheme in the address.
Referencing the SEI
serviceClass
attribute of the cxf:cxfEndpoint
element references the SEI of the Web service, which in this case is the CustomerService
interface.
37.4. Sort Messages by Operation Name
The operationName header
operationName
header to the name of the invoked operation. You can then use this header to sort messages by operation name.
Sorting by operation name
customer-ws-camel-cxf-pojo
demonstration defines the following route, which uses the content-based router pattern to sort incoming messages, based on the operation name. The when
predicates check the value of the operationName
header using simple language expressions, sorting messages into invocations on the updateCustomer
operation, the lookupCustomer
operation, or the getCustomerStatus
operation.
<beans ...> ... <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="cxf:bean:customer-ws"/> <choice> <when> <simple>${in.header.operationName} == 'updateCustomer'</simple> <to uri="updateCustomer"/> </when> <when> <simple>${in.header.operationName} == 'lookupCustomer'</simple> <to uri="lookupCustomer"/> </when> <when> <simple>${in.header.operationName} == 'getCustomerStatus'</simple> <to uri="getCustomerStatus"/> </when> </choice> </route> </camelContext> <bean id="updateCustomer" class="com.fusesource.customerwscamelcxfpojo.UpdateCustomerProcessor"/> <bean id="getCustomerStatus" class="com.fusesource.customerwscamelcxfpojo.GetCustomerStatusProcessor"/> <bean id="lookupCustomer" class="com.fusesource.customerwscamelcxfpojo.LookupCustomerProcessor"/> </beans>
Beans as endpoints
choice
DSL to a different processor bean. The DSL for sending exchanges to producer endpoints (for example, <to uri="Destination"/>
) is integrated with the bean registry: if the Destination does not resolve to an endpoint or a component, the Destination is used as a bean ID to look up the bean registry. In this example, the exchange is routed to processor beans (which implement the org.apache.camel.Processor
interface).
37.5. Process Operation Parameters
Overview
Contents of request message body
org.apache.cxf.message.MessageContentsList
object. You can also obtain the message body as an Object[]
array (where type conversion is automatic).
Object[]
array, the array contains the list of all the operation's IN, INOUT, and OUT parameters in exactly the same order as defined in the WSDL contract (and in the same order as the corresponding operation signature of the SEI). The parameter mode affects the content as follows:
IN
- Contains a parameter value from the client.
INOUT
- Contains a
Holder
object containing a parameter value from the client. OUT
- Contains an empty
Holder
object, which is a placeholder for the response.
Object[]
array to represent a return value.
Contents of response message body
org.apache.cxf.message.MessageContentsList
object or an Object[]
array.
Object[]
array, the array should contain only the operation's INOUT and OUT parameters in the same order as defined in the WSDL contract, omitting the IN parameters. The parameter mode affects the content as follows:
INOUT
- Contains a
Holder
object, which you must set to a response value. TheHolder
object used here must be exactly theHolder
object for the corresponding parameter that was extracted from the requestObject[]
array. Creating and inserting a newHolder
object into theObject[]
array does not work. OUT
- Contains a
Holder
object, which you must initialize with a response value. TheHolder
object used here must be exactly theHolder
object for the corresponding parameter that was extracted from the requestObject[]
array. Creating and inserting a newHolder
object into theObject[]
array does not work.
Object[]
array. The return type is set as a plain object: it does not use a Holder
object.
Example: getCustomerStatus operation
getCustomerStatus
operation takes three parameters: IN, OUT, and OUT, respectively. The corresponding method signature in the SEI is, as follows:
// Java public void getCustomerStatus( @WebParam(name = "customerId", targetNamespace = "") java.lang.String customerId, @WebParam(mode = WebParam.Mode.OUT, name = "status", targetNamespace = "") javax.xml.ws.Holder<java.lang.String> status, @WebParam(mode = WebParam.Mode.OUT, name = "statusMessage", targetNamespace = "") javax.xml.ws.Holder<java.lang.String> statusMessage );
Example: request and response bodies
getCustomerStatus
operation, the bodies of the request message and the response message have the following contents:
- Request message—as an
Object[]
array type, the contents are:{ String customerId, Holder<String> status, Holder<String> statusMessage }
. - Response message—as an
Object[]
array type, the contents are:{Holder<String> status, Holder<String> statusMessage }
Example: processing getCustomerStatus
GetCustomerStatusProcessor
class is responsible for processing incoming getCustomerStatus
invocations. The following sample implementation for POJO mode shows how to read the request parameters from the In message body and then set the response parameters in the Out message body.
// Java package com.fusesource.customerwscamelcxfpojo; import javax.xml.ws.Holder; import org.apache.camel.Exchange; import org.apache.camel.Processor; import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class GetCustomerStatusProcessor implements Processor { public static final Logger log = LoggerFactory.getLogger(GetCustomerStatusProcessor.class); public void process(Exchange exchng) throws Exception { Object[] args = exchng.getIn().getBody(Object[].class); String id = (String) args[0]; Holder<String> status = (Holder<String>) args[1]; Holder<String> statusMsg = (Holder<String>) args[2]; log.debug("Getting status for customer '" + id + "'"); // This is where you'd actually do the work! Setting // the holder values to constants for the sake of brevity. // status.value = "Offline"; statusMsg.value = "Going to sleep now!"; exchng.getOut().setBody(new Object[] {status , statusMsg}); } }
37.6. Deploy to OSGi
Overview
- Bundles are a relatively lightweight deployment option (because dependencies can be shared between deployed bundles).
- OSGi provides sophisticated dependency management, ensuring that only version-consistent dependencies are added to the bundle's classpath.
Using the Maven bundle plug-in
pom.xml
file:
- Change the packaging type to
bundle
(by editing the value of theproject/packaging
element in the POM). - Add the Maven bundle plug-in to your POM file and configure it as appropriate.
Sample bundle plug-in configuration
<?xml version="1.0"?>
<project ...>
...
<groupId>com.fusesource.byexample.cxf-webinars</groupId>
<artifactId>customer-ws-camel-cxf-pojo</artifactId>
<name>customer-ws-camel-cxf-pojo</name>
<packaging>bundle</packaging>
...
<build>
<plugins>
...
<plugin>
<groupId>org.apache.felix</groupId>
<artifactId>maven-bundle-plugin</artifactId>
<extensions>true</extensions>
<configuration>
<instructions>
<Import-Package>
*
</Import-Package>
<DynamicImport-Package>
org.apache.cxf.*,
org.springframework.beans.*
</DynamicImport-Package>
</instructions>
</configuration>
</plugin>
...
</plugins>
</build>
</project>
Dynamic imports
DynamicImport-Package
element). This is a pragmatic way of dealing with the fact that Spring XML files are not terribly well integrated with the Maven bundle plug-in. At build time, the Maven bundle plug-in is not able to figure out which Java classes are required by the Spring XML code. By listing wildcarded package names in the DynamicImport-Package
element, however, you allow the OSGi container to figure out which Java classes are needed by the Spring XML code at run time.
DynamicImport-Package
headers is not recommended in OSGi, because it short-circuits OSGi version checking. Normally, what should happen is that the Maven bundle plug-in lists the Java packages used at build time, along with their versions, in the Import-Package
header. At deploy time, the OSGi container then checks that the available Java packages are compatible with the build time versions listed in the Import-Package
header. With dynamic imports, this version checking cannot be performed.
Build and deploy the POJO route bundle
mvn install
karaf@root> install -s mvn:com.fusesource.byexample.cxf-webinars/customer-ws-camel-cxf-pojo
org.ops4j.pax.url.mvn.localRepository
property in the EsbInstallDir/etc/org.ops4j.pax.url.mvn.cfg
file, before you can use the mvn:
scheme to access Maven artifacts.
Chapter 38. Payload-Based Route
38.1. Processing Messages in PAYLOAD Format
Overview
org.w3c.dom.Node
type). One of the advantages of the PAYLOAD format is that no JAX-WS and JAXB stub code is required, which allows your application to be dynamic, potentially handling many different WSDL interfaces.
Demonstration location
cxf-webinars-jboss-fuse-6.2/customer-ws-camel-cxf-payload
Camel CXF component
cxf:cxfEndpoint
XML element and are implemented by the Apache Camel project—are not to be confused with the Apache CXF JAX-WS endpoints—which are instantiated using the jaxws:endpoint
XML element and are implemented by the Apache CXF project.
PAYLOAD data format
dataFormat=PAYLOAD
option on a Camel CXF endpoint URI and it has the following characteristics:
- Enables you to access the message body as a DOM object (XML payload).
- No JAX-WS or JAXB stub code required.
- The SOAP body is marshalled as follows:
- The message body is effectively an XML payload of
org.w3c.dom.Node
type (wrapped in aCxfPayload
object). - The type of the message body is
org.apache.camel.component.cxf.CxfPayload
.
- The SOAP headers are converted into headers in the exchange's In message, of
org.apache.cxf.binding.soap.SoapHeader
type.
Implementing and building a PAYLOAD route
- Instantiate the Camel CXF endpoint in Spring, using the
cxf:cxfEndpoint
element. - Implement the route in XML, where you can use the content-based router to sort requests by operation name.
- For each operation, define a processor bean to process the request.
- Define velocity templates for generating the reponse messages.
Sample PAYLOAD route
CustomerService
Web service using the PAYLOAD data format. After sorting the request messages by operation name, an operation-specific processor bean reads the incoming request parameters. Finally, the response messages are generated using Velocity templates.
Figure 38.1. Sample PAYLOAD Route
38.2. Instantiate the WS Endpoint
Overview
- Consumer endpoint—(at the start of a route) represents a Web service instance, which integrates with the route. The type of payload injected into the route depends on the value of the endpoint's
dataFormat
option. - Producer endpoint—represents a special kind of WS client proxy, which converts the current exchange object into an operation invocation on a remote Web service. The format of the current exchange must match the endpoint's
dataFormat
setting.
The cxf:bean: URI syntax
cxf:bean:
URI is used to bind an Apache CXF endpoint to a route and has the following general syntax:
cxf:bean:CxfEndpointID[?Options]
CxfEndpointID
is the ID of a bean created using the cxf:cxfEndpoint
element, which configures the details of the WS endpoint. You can append options to this URI (where the options are described in detail in chapter "CXF" in "Apache Camel Component Reference"). To enable payload mode, you must set the URI option, dataFormat=PAYLOAD
.
customer-ws
bean, define the route as follows:
<route>
<from uri="cxf:bean:customer-ws?dataFormat=PAYLOAD"/>
...
</route>
The cxf:cxfEndpoint element
cxf:cxfEndpoint
element is used to define a WS endpoint that binds either to the start (consumer endpoint) or the end (producer endpoint) of a route. For example, to define the customer-ws
WS endpoint in PAYLOAD mode, you define a cxf:cxfEndpoint
element as follows:
<?xml version="1.0" encoding="UTF-8"?> <beans ...> ... <cxf:cxfEndpoint id="customer-ws" address="/Customer" endpointName="c:SOAPOverHTTP" serviceName="c:CustomerService" wsdlURL="wsdl/CustomerService.wsdl" xmlns:c="http://demo.fusesource.com/wsdl/CustomerService/"/> ... </beans>
Address for the Jetty container
address
attribute of cxf:cxfEndpoint
is therefore used to configure the addressing information for the endpoint in the Jetty container.
- Address syntax for default servlet container—to use the default servlet container, specify only the servlet context for this endpoint. Do not specify the protocol, host, and IP port in the address. For example, to deploy the endpoint to the
/Customer
servlet context in the default servlet container:address="/Customer"
- Address syntax for custom servlet container—to instantiate a custom Jetty container for this endpoint, specify a complete HTTP URL, including the host and IP port (the value of the IP port effectively identifies the target Jetty container). Typically, for a Jetty container, you specify the host as
0.0.0.0
, which is interpreted as a wildcard that matches every IP network interface on the local machine (that is, if deployed on a multi-homed host, Jetty opens a listening port on every network card). For example, to deploy the endpoint to the custom Jetty container listening on IP port,8083
:address="http://0.0.0.0:8083/Customer"
NoteIf you want to configure a secure endpoint (secured by SSL), you would specify thehttps:
scheme in the address.
Specifying the WSDL location
wsdlURL
attribute of the cxf:cxfEndpoint
element is used to specify the location of the WSDL contract for this endpoint. The WSDL contract is used exclusively as the source of metadata for this endpoint: there is need to specify an SEI in PAYLOAD mode.
38.3. Sort Messages by Operation Name
The operationName header
operationName
header to the name of the invoked operation. You can then use this header to sort messages by operation name.
Sorting by operation name
customer-ws-camel-cxf-payload
demonstration defines the following route, which uses the content-based router pattern to sort incoming messages, based on the operation name. The when
predicates check the value of the operationName
header using simple language expressions, sorting messages into invocations on the updateCustomer
operation, the lookupCustomer
operation, or the getCustomerStatus
operation.
<beans ...> ... <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="cxf:bean:customer-ws?dataFormat=PAYLOAD"/> <choice> <when> <simple>${in.header.operationName} == 'updateCustomer'</simple> ... </when> <when> <simple>${in.header.operationName} == 'lookupCustomer'</simple> ... </when> <when> <simple>${in.header.operationName} == 'getCustomerStatus'</simple> ... </when> </choice> </route> </camelContext> </beans>
38.4. SOAP/HTTP-to-JMS Bridge Use Case
Overview
Figure 38.2. SOAP/HTTP-to-JMS Bridge
Transforming RPC operations to One Way
- The WS client invokes a synchronous operation on the Camel CXF endpoint at the start of the route. The Camel CXF endpoint then creates an initial InOut exchange at the start of the route, where the body of the exchange message contains a payload in XML format.
- The
inOnly
DSL command pushes a copy of the XML payload onto a JMS queue, so that it can be processed offline at some later time. - The
transform
DSL command constructs an immediate response to send back to the client, where the response has the form of an XML string. - The Camel CXF component supports implicit type conversion of the XML string to payload format.
- The response is sent back to the WS client, thus completing the synchronous operation invocation.
Creating a broker instance
amq:broker
element in the Spring XML file, as follows:
<beans xmlns="http://www.springframework.org/schema/beans" ... xmlns:amq="http://activemq.apache.org/schema/core" ...> <amq:broker brokerName="CxfPayloadDemo" persistent="false"> <amq:transportConnectors> <amq:transportConnector name="openwire" uri="tcp://localhost:51616"/> <amq:transportConnector name="vm" uri="vm:local"/> </amq:transportConnectors> </amq:broker> ... </beans>
persistent
attribute set to false
, so that the messages are stored only in memory.
Configuring the JMS component
<beans ...> ... <bean id="activemq" class="org.apache.activemq.camel.component.ActiveMQComponent"> <property name="brokerURL" value="vm:local"/> </bean> ... </beans>
id
value of activemq
, you are implicitly overriding the component associated with the endpoint URI prefix, activemq:
. In other words, your custom ActiveMQComponent
instance is used instead of the default ActiveMQComponent
instance from the camel-activemq
JAR file.
Sample SOAP/HTTP-to-JMS route
updateCustomer
operation from the CustomerService
SEI, as follows:
<when> <simple>${in.header.operationName} == 'updateCustomer'</simple> <log message="Placing update customer message onto queue."/> <inOnly uri="activemq:queue:CustomerUpdates?jmsMessageType=Text"/> <transform> <constant> <![CDATA[ <ns2:updateCustomerResponse xmlns:ns2="http://demo.fusesource.com/wsdl/CustomerService/"/> ]]> </constant> </transform> </when>
Sending to the JMS endpoint in inOnly mode
inOnly
DSL command instead of the to
DSL command. When you send a message using the to
DSL command, the default behavior is to use the same invocation mode as the current exchange. But the current exchange has an InOut MEP, which means that the to
DSL command would wait forever for a response message from JMS.
inOnly
DSL command into the route.
jmsMessageType=Text
, Camel CXF implicitly converts the message payload to an XML string before pushing it onto the JMS queue.
Returning a literal response value
transform
DSL command uses an expression to set the body of the exchange's Out message and this message is then used as the response to the client. Your first impulse when defining a response in XML format might be to use a DOM API, but in this example, the response is specified as a string literal. This approach has the advantage of being both efficient and very easy to program.
38.5. Generating Responses Using Templates
Overview
Figure 38.3. Response Generated by Velocity
Sample template-based route
getCustoemrStatus
operation, as follows:
... <when> <simple>${in.header.operationName} == 'getCustomerStatus'</simple> <convertBodyTo type="org.w3c.dom.Node"/> <setHeader headerName="customerId"> <xpath>/cus:getCustomerStatus/customerId/text()</xpath> </setHeader> <to uri="getCustomerStatus"/> <to uri="velocity:getCustomerStatusResponse.vm"/> </when> </choice> </route> </camelContext ... <bean id="getCustomerStatus" class="com.fusesource.customerwscamelcxfpayload.GetCustomerStatus"/>
Route processing steps
getCustomerStatus
would be processed as follows:
- To facilitate processing the payload body, the first step uses
convertBodyTo
to convert the body type fromorg.apache.camel.component.cxf.CxfPayload
(the default payload type) toorg.w3c.dom.Node
. - The route then applies an XPath expression to the message in order to extract the customer ID value and then stashes it in the
customerId
header. - The next step sends the message to the
getCustomerStatus
bean, which does whatever processing is required to get the customer status for the specified customer ID. The results from this step are stashed in message headers. - Finally, a response is generated using a velocity template.
Converting XPath result to a string
- Specify the result type explicitly using the
resultType
attribute, as follows:<xpath resultType="java.lang.String">/cus:getCustomerStatus/customerId</xpath>
- Modify the expression so that it returns a
text()
node, which automatically converts to string:<xpath>/cus:getCustomerStatus/customerId/text()</xpath>
getCustomerStatus processor bean
getCustomerStatus
processor bean is an instance of the GetCustomerStatus
processor class, which is defined as follows:
// Java package com.fusesource.customerwscamelcxfpayload; import org.apache.camel.Exchange; import org.apache.camel.Processor; public class GetCustomerStatus implements Processor { public void process(Exchange exchng) throws Exception { String id = exchng.getIn().getHeader("customerId", String.class); // Maybe do some kind of lookup here! // exchng.getIn().setHeader("status", "Away"); exchng.getIn().setHeader("statusMessage", "Going to sleep."); } }
status
and statusMessage
are simply set to constant values and stashed in message headers.
null
, the next processor in the route gets a copy of the current In message instead
null
.
getCustomerStatusResponse.vm Velocity template
${header.HeaderName}
substitutes the value of a named header.
getCustomerStatus
reponse is located in the customer-ws-camel-cxf-payload/src/main/resources
directory and it contains the following template script:
<ns2:getCustomerStatusResponse xmlns:ns2="http://demo.fusesource.com/wsdl/CustomerService/"> <status>${headers.status}</status> <statusMessage>${headers.statusMessage}</statusMessage> </ns2:getCustomerStatusResponse>
38.6. TypeConverter for CXFPayload
Overview
String
objects to CXFPayload
objects. This type converter automatically gets invoked at the end of the Camel route, when the generated response message (which is a String
type) gets converted into a CXFPayload
object.
String to CXFPayload type converter
String
to CXFPayload
type converter is implemented in the AdditionalCxfPayloadConverters
class, as follows:
// Java
package com.fusesource.customerwscamelcxfpayload;
import java.io.ByteArrayInputStream;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.apache.camel.Converter;
import org.apache.camel.component.cxf.CxfPayload;
import org.apache.cxf.binding.soap.SoapHeader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
@Converter
public class AdditionalCxfPayloadConverters {
...
@Converter
public static CxfPayload<SoapHeader> toCxfPayload(String xml) {
// System.out.println("To CxfPayload " + xml);
List<Element> elements = new ArrayList<Element>();
try {
Document doc = b.newDocumentBuilder().parse(new ByteArrayInputStream(xml.getBytes()));
elements.add(doc.getDocumentElement());
} catch (Exception ex) {
log.warn("Exception while converting String payload to CxfPayload; resulting payload will be empty.");
}
// The CxfPayload is changed to use Source object under layer, the elements API only work if we already setup the list before creating the CxfPayload
CxfPayload<SoapHeader> ret = new CxfPayload<SoapHeader>(null, elements);
return ret;
}
...
}
Reference
38.7. Deploy to OSGi
Overview
- Bundles are a relatively lightweight deployment option (because dependencies can be shared between deployed bundles).
- OSGi provides sophisticated dependency management, ensuring that only version-consistent dependencies are added to the bundle's classpath.
Using the Maven bundle plug-in
pom.xml
file:
- Change the packaging type to
bundle
(by editing the value of theproject/packaging
element in the POM). - Add the Maven bundle plug-in to your POM file and configure it as appropriate.
Sample bundle plug-in configuration
<?xml version="1.0"?>
<project ...>
...
<groupId>com.fusesource.byexample.cxf-webinars</groupId>
<artifactId>customer-ws-camel-cxf-payload</artifactId>
<name>customer-ws-camel-cxf-payload</name>
<packaging>bundle</packaging>
...
<build>
<plugins>
...
<plugin>
<groupId>org.apache.felix</groupId>
<artifactId>maven-bundle-plugin</artifactId>
<extensions>true</extensions>
<configuration>
<instructions>
<Import-Package>
org.apache.camel.component.velocity,
javax.jws,
javax.wsdl,
javax.xml.bind,
javax.xml.bind.annotation,
javax.xml.namespace,
javax.xml.ws,
org.w3c.dom,
*
</Import-Package>
<DynamicImport-Package>
org.apache.cxf.*,
org.springframework.beans.*
</DynamicImport-Package>
</instructions>
</configuration>
</plugin>
...
</plugins>
</build>
</project>
Dynamic imports
DynamicImport-Package
element). This is a pragmatic way of dealing with the fact that Spring XML files are not terribly well integrated with the Maven bundle plug-in. At build time, the Maven bundle plug-in is not able to figure out which Java classes are required by the Spring XML code. By listing wildcarded package names in the DynamicImport-Package
element, however, you allow the OSGi container to figure out which Java classes are needed by the Spring XML code at run time.
DynamicImport-Package
headers is not recommended in OSGi, because it short-circuits OSGi version checking. Normally, what should happen is that the Maven bundle plug-in lists the Java packages used at build time, along with their versions, in the Import-Package
header. At deploy time, the OSGi container then checks that the available Java packages are compatible with the build time versions listed in the Import-Package
header. With dynamic imports, this version checking cannot be performed.
Build and deploy the client bundle
mvn install
camel-velocity
feature, which is needed for this example:
karaf@root> features:install camel-velocity
karaf@root> install -s mvn:com.fusesource.byexample.cxf-webinars/customer-ws-camel-cxf-payload
org.ops4j.pax.url.mvn.localRepository
property in the InstallDir/etc/org.ops4j.pax.url.mvn.cfg
file, before you can use the mvn:
scheme to access Maven artifacts.
Chapter 39. Provider-Based Route
39.1. Provider-Based JAX-WS Endpoint
Overview
SAXSource
. Since the XMLstreaming types are more efficient than DOM objects, the provider-based approach is ideal for large XML messages.
Demonstration location
cxf-webinars-jboss-fuse-6.2/customer-ws-camel-cxf-provider
Camel CXF component
cxf:cxfEndpoint
XML element and are implemented by the Apache Camel project—are not to be confused with the Apache CXF JAX-WS endpoints—which are instantiated using the jaxws:endpoint
XML element and are implemented by the Apache CXF project.
Provider-based approach and the PAYLOAD data format
- Define a custom
javax.xml.ws.Provider<StreamType>
class, where the StreamType type is an XML streaming type, such asSAXSource
. - The PAYLOAD data format is selected by an annotation on the custom
Provider<?>
class (see the section called “The SAXSourceService provider class”). - The custom
Provider<?>
class is referenced by setting theserviceClass
attribute of thecxf:cxfEndpoint
element in XML configuration.
- Enables you to access the message body as a streamed XML type—for example,
javax.xml.transform.sax.SAXSource
. - No JAX-WS or JAXB stub code required.
- The SOAP body is marshalled into a stream-based
SAXSource
type. - The SOAP headers are converted into headers in the exchange's In message, of
org.apache.cxf.binding.soap.SoapHeader
type.
Implementing and building a provider-based route
- Define a custom
javax.xml.ws.Provider<StreamType>
class (the current demonstration usesSAXSource
as the StreamType type). - Instantiate the Camel CXF endpoint in Spring, using the
cxf:cxfEndpoint
element and reference the custom provider class (using theserviceClass
attribute). - Implement the route in XML, where you can use the content-based router to sort requests by operation name.
- For each operation, define a processor bean to process the request.
- Define velocity templates for generating the reponse messages.
- Define a custom type converter, to support converting a
String
message body to aSAXSource
message body.
Sample provider-based route
CustomerService
Web service using the provider-based approach. After sorting the request messages by operation name, an operation-specific processor bean reads the incoming request parameters. Finally, the response messages are generated using Velocity templates.
Figure 39.1. Sample Provider-Based Route
39.2. Create a Provider<?> Implementation Class
Overview
Provider<>
class that implements the invoke()
method. In fact, the sole purpose of this class is to provide runtime type information for Apache CXF: the invoke()
method never gets called!
SAXSource
.
The SAXSourceService provider class
SAXSourceService
, is as follows:
// Java package com.fusesource.customerwscamelcxfprovider; import javax.xml.transform.sax.SAXSource; import javax.xml.ws.Provider; import javax.xml.ws.Service.Mode; import javax.xml.ws.ServiceMode; import javax.xml.ws.WebServiceProvider; @WebServiceProvider() @ServiceMode(Mode.PAYLOAD) public class SAXSourceService implements Provider<SAXSource> { public SAXSource invoke(SAXSource t) { throw new UnsupportedOperationException("Not supported yet."); } }
SAXSourceService
, must be annotated by the @WebServiceProvider
annotation to mark it as a provider class and can be optionally annotated by the @ServiceMode
annotation to select PAYLOAD mode.
39.3. Instantiate the WS Endpoint
Overview
- Consumer endpoint—(at the start of a route) represents a Web service instance, which integrates with the route. The type of payload injected into the route depends on the value of the endpoint's
dataFormat
option. - Producer endpoint—represents a special kind of WS client proxy, which converts the current exchange object into an operation invocation on a remote Web service. The format of the current exchange must match the endpoint's
dataFormat
setting.
The cxf:bean: URI syntax
cxf:bean:
URI is used to bind an Apache CXF endpoint to a route and has the following general syntax:
cxf:bean:CxfEndpointID[?Options]
CxfEndpointID
is the ID of a bean created using the cxf:cxfEndpoint
element, which configures the details of the WS endpoint. You can append options to this URI (where the options are described in detail in chapter "CXF" in "Apache Camel Component Reference"). Provider mode is essentially a variant of PAYLOAD mode: you could specify this mode on the URI (by setting dataFormat=PAYLOAD
), but this is not necessary, because PAYLOAD mode is already selected by the @ServiceMode
annotation on the custom Provider
class.
customer-ws
bean, define the route as follows:
<route> <from uri="cxf:bean:customer-ws"/> ... </route>
The cxf:cxfEndpoint element
cxf:cxfEndpoint
element is used to define a WS endpoint that binds either to the start (consumer endpoint) or the end (producer endpoint) of a route. For example, to define the customer-ws
WS endpoint in provider mode, you define a cxf:cxfEndpoint
element as follows:
<?xml version="1.0" encoding="UTF-8"?> <beans ...> ... <cxf:cxfEndpoint id="customer-ws" address="/Customer" endpointName="c:SOAPOverHTTP" serviceName="c:CustomerService" wsdlURL="wsdl/CustomerService.wsdl" serviceClass="com.fusesource.customerwscamelcxfprovider.SAXSourceService" xmlns:c="http://demo.fusesource.com/wsdl/CustomerService/"/> ... </beans>
Specifying the WSDL location
wsdlURL
attribute of the cxf:cxfEndpoint
element is used to specify the location of the WSDL contract for this endpoint. The WSDL contract is used as the source of metadata for this endpoint.
Specifying the service class
serviceClass
attribute must be set to the provider class, SAXSourceService
.
39.4. Sort Messages by Operation Name
The operationName header
operationName
header to the name of the invoked operation. You can then use this header to sort messages by operation name.
Sorting by operation name
customer-ws-camel-cxf-provider
demonstration defines the following route, which uses the content-based router pattern to sort incoming messages, based on the operation name. The when
predicates check the value of the operationName
header using simple language expressions, sorting messages into invocations on the updateCustomer
operation, the lookupCustomer
operation, or the getCustomerStatus
operation.
<beans ...> ... <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="cxf:bean:customer-ws"/> <choice> <when> <simple>${in.header.operationName} == 'updateCustomer'</simple> ... </when> <when> <simple>${in.header.operationName} == 'lookupCustomer'</simple> ... </when> <when> <simple>${in.header.operationName} == 'getCustomerStatus'</simple> ... </when> </choice> </route> </camelContext> ... </beans>
39.5. SOAP/HTTP-to-JMS Bridge Use Case
Overview
Figure 39.2. SOAP/HTTP-to-JMS Bridge
Transforming RPC operations to One Way
- The WS client invokes a synchronous operation on the Camel CXF endpoint at the start of the route. The Camel CXF endpoint then creates an initial InOut exchange at the start of the route, where the body of the exchange message contains a payload in XML format.
- The
inOnly
DSL command pushes a copy of the XML payload onto a JMS queue, so that it can be processed offline at some later time. - The
transform
DSL command constructs an immediate response to send back to the client, where the response has the form of an XML string. - The route explicitly converts the XML string to the
javax.xml.transform.sax.SAXSource
type. - The response is sent back to the WS client, thus completing the synchronous operation invocation.
Creating a broker instance
amq:broker
element in the Spring XML file, as follows:
<beans xmlns="http://www.springframework.org/schema/beans" ... xmlns:amq="http://activemq.apache.org/schema/core" ...> <amq:broker brokerName="CxfPayloadDemo" persistent="false"> <amq:transportConnectors> <amq:transportConnector name="openwire" uri="tcp://localhost:51616"/> <amq:transportConnector name="vm" uri="vm:local"/> </amq:transportConnectors> </amq:broker> ... </beans>
persistent
attribute set to false
, so that the messages are stored only in memory.
Configuring the JMS component
<beans ...> ... <bean id="activemq" class="org.apache.activemq.camel.component.ActiveMQComponent"> <property name="brokerURL" value="vm:local"/> </bean> ... </beans>
id
value of activemq
, you are implicitly overriding the component associated with the endpoint URI prefix, activemq:
. In other words, your custom ActiveMQComponent
instance is used instead of the default ActiveMQComponent
instance from the camel-activemq
JAR file.
Sample SOAP/HTTP-to-JMS route
updateCustomer
operation from the CustomerService
SEI, as follows:
<when> <simple>${in.header.operationName} == 'updateCustomer'</simple> <log message="Placing update customer message onto queue."/> <inOnly uri="activemq:queue:CustomerUpdates?jmsMessageType=Text"/> <transform> <constant> <![CDATA[ <ns2:updateCustomerResponse xmlns:ns2="http://demo.fusesource.com/wsdl/CustomerService/"/> ]]> </constant> </transform> <convertBodyTo type="javax.xml.transform.sax.SAXSource"/> </when>
Sending to the JMS endpoint in inOnly mode
inOnly
DSL command instead of the to
DSL command. When you send a message using the to
DSL command, the default behavior is to use the same invocation mode as the current exchange. But the current exchange has an InOut MEP, which means that the to
DSL command would wait forever for a response message from JMS.
inOnly
DSL command into the route.
jmsMessageType=Text
, Camel CXF implicitly converts the message payload to an XML string before pushing it onto the JMS queue.
Returning a literal response value
transform
DSL command uses an expression to set the body of the exchange's Out message and this message is then used as the response to the client. Your first impulse when defining a response in XML format might be to use a DOM API, but in this example, the response is specified as a string literal. This approach has the advantage of being both efficient and very easy to program.
Type conversion of the response message
javax.xml.transform.sax.SAXSource
. In the last step of the route, therefore, you must convert the message body from String
type to javax.xml.transform.sax.SAXSource
type, by invoking the convertBodyTo
DSL command.
SAXSource
conversion is provided by a custom type converter, as described in Section 39.7, “TypeConverter for SAXSource”.
39.6. Generating Responses Using Templates
Overview
Figure 39.3. Response Generated by Velocity
Sample template-based route
getCustoemrStatus
operation, as follows:
... <when> <simple>${in.header.operationName} == 'getCustomerStatus'</simple> <setHeader headerName="customerId"> <xpath resultType="java.lang.String">/cus:getCustomerStatus/customerId</xpath> </setHeader> <to uri="getCustomerStatus"/> <to uri="velocity:getCustomerStatusResponse.vm"/> <convertBodyTo type="javax.xml.transform.sax.SAXSource"/> </when> </choice> </route> </camelContext ... <bean id="getCustomerStatus" class="com.fusesource.customerwscamelcxfpayload.GetCustomerStatus"/>
Route processing steps
getCustomerStatus
would be processed as follows:
- The route applies an XPath expression to the message in order to extract the customer ID value and then stashes it in the
customerId
header. - The next step sends the message to the
getCustomerStatus
bean, which does whatever processing is required to get the customer status for the specified customer ID. The results from this step are stashed in message headers. - A response is generated using a Velocity template.
- Finally, the XML string generated by the Velocity template must be explicitly converted to the
javax.xml.transform.sax.SAXSource
type usingconvertBodyTo
(which implicitly relies on a type converter).
XPath expressions and SAXSource
getCustomerStatus processor bean
getCustomerStatus
processor bean is an instance of the GetCustomerStatus
processor class, which is defined as follows:
// Java package com.fusesource.customerwscamelcxfpayload; import org.apache.camel.Exchange; import org.apache.camel.Processor; public class GetCustomerStatus implements Processor { public void process(Exchange exchng) throws Exception { String id = exchng.getIn().getHeader("customerId", String.class); // Maybe do some kind of lookup here! // exchng.getIn().setHeader("status", "Away"); exchng.getIn().setHeader("statusMessage", "Going to sleep."); } }
status
and statusMessage
are simply set to constant values and stashed in message headers.
getCustomerStatusResponse.vm Velocity template
${header.HeaderName}
substitutes the value of a named header.
getCustomerStatus
reponse is located in the customer-ws-camel-cxf-provider/src/main/resources
directory and it contains the following template script:
<ns2:getCustomerStatusResponse xmlns:ns2="http://demo.fusesource.com/wsdl/CustomerService/"> <status>${headers.status}</status> <statusMessage>${headers.statusMessage}</statusMessage> </ns2:getCustomerStatusResponse>
39.7. TypeConverter for SAXSource
Overview
String
objects to SAXSource
objects.
String to SAXSource type converter
String
to SAXSource
type converter is implemented in the AdditionalConverters
class, as follows:
// Java package com.fusesource.customerwscamelcxfprovider; import java.io.ByteArrayInputStream; import javax.xml.transform.sax.SAXSource; import org.apache.camel.Converter; import org.xml.sax.InputSource; @Converter public class AdditionalConverters { @Converter public static SAXSource toSAXSource(String xml) { return new SAXSource(new InputSource(new ByteArrayInputStream(xml.getBytes()))); } }
Reference
39.8. Deploy to OSGi
Overview
- Bundles are a relatively lightweight deployment option (because dependencies can be shared between deployed bundles).
- OSGi provides sophisticated dependency management, ensuring that only version-consistent dependencies are added to the bundle's classpath.
Using the Maven bundle plug-in
pom.xml
file:
- Change the packaging type to
bundle
(by editing the value of theproject/packaging
element in the POM). - Add the Maven bundle plug-in to your POM file and configure it as appropriate.
Sample bundle plug-in configuration
<?xml version="1.0"?>
<project ...>
...
<groupId>com.fusesource.byexample.cxf-webinars</groupId>
<artifactId>customer-ws-camel-cxf-provider</artifactId>
<name>customer-ws-camel-cxf-provider</name>
<packaging>bundle</packaging>
...
<build>
<plugins>
...
<plugin>
<groupId>org.apache.felix</groupId>
<artifactId>maven-bundle-plugin</artifactId>
<extensions>true</extensions>
<configuration>
<instructions>
<Import-Package>
org.apache.camel.component.velocity,
javax.jws,
javax.wsdl,
javax.xml.bind,
javax.xml.bind.annotation,
javax.xml.namespace,
javax.xml.ws,
org.w3c.dom,
*
</Import-Package>
<DynamicImport-Package>
org.apache.cxf.*,
org.springframework.beans.*
</DynamicImport-Package>
</instructions>
</configuration>
</plugin>
...
</plugins>
</build>
</project>
Dynamic imports
DynamicImport-Package
element). This is a pragmatic way of dealing with the fact that Spring XML files are not terribly well integrated with the Maven bundle plug-in. At build time, the Maven bundle plug-in is not able to figure out which Java classes are required by the Spring XML code. By listing wildcarded package names in the DynamicImport-Package
element, however, you allow the OSGi container to figure out which Java classes are needed by the Spring XML code at run time.
DynamicImport-Package
headers is not recommended in OSGi, because it short-circuits OSGi version checking. Normally, what should happen is that the Maven bundle plug-in lists the Java packages used at build time, along with their versions, in the Import-Package
header. At deploy time, the OSGi container then checks that the available Java packages are compatible with the build time versions listed in the Import-Package
header. With dynamic imports, this version checking cannot be performed.
Build and deploy the client bundle
mvn install
karaf@root> install -s mvn:com.fusesource.byexample.cxf-webinars/customer-ws-camel-cxf-provider
org.ops4j.pax.url.mvn.localRepository
property in the EsbInstallDir/etc/org.ops4j.pax.url.mvn.cfg
file, before you can use the mvn:
scheme to access Maven artifacts.
Chapter 40. Proxying a Web Service
Abstract
40.1. Proxying with HTTP
Overview
Figure 40.1. Proxy Route with Message in HTTP Format
Alternatives for the consumer endpoint
- Jetty endpoint—is a lightweight Web server. You can use Jetty to handle messages for any HTTP-based protocol, including the commonly-used Web service SOAP/HTTP protocol.
- Camel CXF endpoint in MESSAGE mode—when a Camel CXF endpoint is used in MESSAGE mode, the body of the exchange message is the raw message received from the transport layer (which is HTTP). In other words, the Camel CXF endpoint in MESSAGE mode is equivalent to a Jetty endpoint in the case of HTTP-based protocols.
Consumer endpoint for HTTP
jetty:HttpAddress
. To configure the Jetty endpoint to be a proxy for a Web service, use a HttpAddress
value that is almost identical to the HTTP address the client connects to, except that Jetty's version of HttpAddress
uses the special hostname, 0.0.0.0
(which matches all of the network interfaces on the current machine).
<route>
<from uri="jetty:http://0.0.0.0:9093/Customers?matchOnUriPrefix=true"/>
...
</route>
matchOnUriPrefix option
http://localhost:9093/Customers
would be accepted, but a request sent to http://localhost:9093/Customers/Foo
would be rejected. By setting matchOnUriPrefix
to true
, however, you enable a kind of wildcarding on the context path, so that any context path prefixed by /Customers
is accepted.
Alternatives for the producer endpoint
- Jetty HTTP client endpoint—(recommended) the Jetty library implements a HTTP client. In particular, the Jetty HTTP client features support for
HttpClient
thread pools, which means that the Jetty implementation scales particularly well. - HTTP endpoint—the HTTP endpoint implements a HTTP client based on the
HttpClient
3.x API. - HTTP4 endpoint—the HTTP endpoint implements a HTTP client based on the
HttpClient
4.x API.
Producer endpoint for HTTP
uri
attribute of the to
element at the end of the route to be the address of the remote Web service, as follows:
<route>
...
<to uri="jetty:http://localhost:8083/Customers?bridgeEndpoint=true&throwExceptionOnFailure=false"/>
</route>
bridgeEndpoint option
bridgeEndpoint
option, which you can enable on a HTTP producer endpoint to configure the endpoint appropriately for operating in a HTTP-to-HTTP bridge (as is the case in this demonstration). In particular, when bridgeEndpoint=true
, the HTTP endpoint ignores the value of the Exchange.HTTP_URI
header, using the HTTP address from the endpoint URI instead.
throwExceptionOnFailure option
throwExceptionOnFailure
to false
ensures that any HTTP exceptions are relayed back to the original WS client, instead of being thrown within the route.
Handling message headers
CamelHttp*
headers set by the consumer endpoint at the start of the route can affect the behavior of the producer endpoint. For this reason, in a bridge application it is advisable to remove the CamelHttp*
headers before the message reaches the producer endpoint, as follows:
<route>
<from uri="jetty:http:..."/>
...
<removeHeaders pattern="CamelHttp*"/>
<to uri="jetty:http:..."/>
</route>
Outgoing HTTP headers
Camel
will be converted into HTTP headers and sent out over the wire by the HTTP producer endpoint. This could have adverse consequences on the behavior of your application, so it is important to be aware of any headers that are set in the exchange object and to remove them, if necessary.
40.2. Proxying with POJO Format
Overview
Figure 40.2. Proxy Route with Message in POJO Format
Consumer endpoint for CXF/POJO
cxf:bean:BeanID
URI format to reference the Camel CXF endpoint as follows (where the dataFormat
option defaults to POJO):
<route>
<from uri="cxf:bean:customerServiceProxy"/>
...
</route>
customerServiceProxy
, is a Camel CXF/POJO endpoint, which is defined as follows:
<?xml version="1.0" encoding="UTF-8"?> <beans ...> ... <cxf:cxfEndpoint id="customerServiceProxy" xmlns:c="http://demo.fusesource.org/wsdl/camelcxf" address="/Customers" endpointName="c:SOAPOverHTTP" serviceName="c:CustomerService" wsdlURL="wsdl/CustomerService.wsdl" serviceClass="org.fusesource.demo.wsdl.camelcxf.CustomerService" /> ... </beans>
Producer endpoint for CXF/POJO
cxf:bean:BeanID
URI format to reference the Camel CXF endpoint as follows (where the dataFormat
option defaults to POJO):
<route>
...
<to uri="cxf:bean:customerServiceReal"/>
</route>
customerServiceReal
, is a Camel CXF/POJO endpoint, which is defined as follows:
<?xml version="1.0" encoding="UTF-8"?> <beans ...> ... <cxf:cxfEndpoint id="customerServiceReal" xmlns:c="http://demo.fusesource.org/wsdl/camelcxf" address="http://localhost:8083/Customers" endpointName="c:SOAPOverHTTP" serviceName="c:CustomerService" wsdlURL="wsdl/CustomerService.wsdl" serviceClass="org.fusesource.demo.wsdl.camelcxf.CustomerService" /> ... </beans>
40.3. Proxying with PAYLOAD Format
Overview
org.w3c.dom.Node
object). The key advantate of using PAYLOAD format is that you can easily process the contents of a message, by accessing the message body as an XML document.
Figure 40.3. Proxy Route with Message in PAYLOAD Format
Consumer endpoint for CXF/PAYLOAD
cxf:bean:BeanID
URI format to reference the Camel CXF endpoint as follows, where you must set the dataFormat
option to PAYLOAD:
<route>
<from uri="cxf:bean:customerServiceProxy?dataFormat=PAYLOAD"/>
...
</route>
customerServiceProxy
, is a Camel CXF/PAYLOAD endpoint, which is defined as follows:
<?xml version="1.0" encoding="UTF-8"?> <beans ...> ... <cxf:cxfEndpoint id="customerServiceProxy" xmlns:c="http://demo.fusesource.org/wsdl/camelcxf" address="/Customers" endpointName="c:SOAPOverHTTP" serviceName="c:CustomerService" wsdlURL="wsdl/CustomerService.wsdl" /> ... </beans>
Producer endpoint for CXF/PAYLOAD
cxf:bean:BeanID
URI format to reference the Camel CXF endpoint as follows, where you must set the dataFormat
option to PAYLOAD:
<route>
...
<to uri="cxf:bean:customerServiceReal?dataFormat=PAYLOAD"/>
</route>
customerServiceReal
, is a Camel CXF/PAYLOAD endpoint, which is defined as follows:
<?xml version="1.0" encoding="UTF-8"?> <beans ...> ... <cxf:cxfEndpoint id="customerServiceReal" xmlns:c="http://demo.fusesource.org/wsdl/camelcxf" address="http://localhost:8083/Customers" endpointName="c:SOAPOverHTTP" serviceName="c:CustomerService" wsdlURL="wsdl/CustomerService.wsdl" /> ... </beans>
Outgoing HTTP headers
Camel
will be converted into HTTP headers and sent out over the wire by the Camel CXF producer endpoint. This could have adverse consequences on the behavior of your application, so it is important to be aware of any headers that are set in the exchange object and to remove them, if necessary.
40.4. Handling HTTP Headers
Overview
HTTP-based components
camel-http
), but also a number of other HTTP-based components, including:
camel-http camel-http4 camel-jetty camel-restlet camel-cxf camel-cxfrs
HTTP headers in Camel CXF
POJO
PAYLOAD
MESSAGE
HTTP consumer endpoint
CamelHttp*
headers- Several headers with the
CamelHttp
prefix are created, which record the status of the incoming message. For details of these internal headers, see HTTP. - HTTP headers
- All of the HTTP headers from the original incoming message are mapped to headers on the exchange's In message.
- URL options (Jetty only)
- The URL options from the original HTTP request URL are mapped to headers on the exchange's In message. For example, given the client request with the URL,
http://myserver/myserver?orderid=123
, a Jetty consumer endpoint creates theorderid
header with value123
.
HTTP producer endpoint
CamelHttp*
- Headers prefixed by
CamelHttp
are used to control the behaviour of the HTTP producer endpoint. Any headers of this kind are consumed by the HTTP producer endpoint and the endpoint behaves as directed.NoteHowever,CamelHttp
message headers are ignored by Camel CXF producer endpoints (but not by Camel CXF-RS producer endpoints). Camel*
- All other headers prefixed by
Camel
are presumed to be meant for internal use and are not mapped to HTTP headers in the target message (in other words, these headers are ignored). *
- All other headers are converted to HTTP headers in the target message, with the exception of the following headers, which are blocked (based on a case-insensitive match):
content-length content-type cache-control connection date pragma trailer transfer-encoding upgrade via warning
Implications for HTTP bridge applications
CamelHttp*
headers set by the consumer endpoint at the start of the route can affect the behavior of the producer endpoint. For this reason, in a bridge application it is advisable to remove the CamelHttp*
headers, as follows:
from("http://0.0.0.0/context/path")
.removeHeaders("CamelHttp*)
...
.to("http://remoteHost/context/path");
Setting a custom header filter
headerFilterStrategy
option on the endpoint URI. For example, to configure a producer endpoint with the myHeaderFilterStrategy
filter, you could use a URI like the following:
http://remoteHost/context/path?headerFilterStrategy=#myHeaderFilterStrategy
myHeaderFilterStrategy
is the bean ID of your custom filter instance.
Chapter 41. Filtering SOAP Message Headers
Abstract
41.1. Basic Configuration
Overview
CxfHeaderFilterStrategy
CxfHeaderFilterStrategy
class. Basic configuration of the CxfHeaderFilterStrategy
class involves setting one or more of the following options:
relayHeaders option
relayHeaders
option can be summarized as follows:
In-band headers | Out-of-band headers | |
relayHeaders=true , dataFormat=PAYLOAD | Filter | Filter |
relayHeaders=true , dataFormat=POJO | Relay all | Filter |
relayHeaders=false | Block | Block |
In-band headers
Out-of-band headers
Payload format
POJO
- (Default) Only out-of-band headers are available for filtering, because the in-band headers have already been processed and removed from the list by CXF. The in-band headers are incorporated into the
MessageContentList
in POJO mode. If you require access to headers in POJO mode, you have the option of implementing a custom CXF interceptor or JAX-WS handler. PAYLOAD
- In this mode, both in-band and out-of-band headers are available for filtering.
MESSAGE
- Not applicable. (In this mode, the message remains in a raw format and the headers are not processed at all.)
Default filter
SoapMessageHeaderFilter
, which removes only the SOAP headers that the SOAP specification expects an intermediate Web service to consume. For more details, see the section called “SoapMessageHeaderFilter”.
Overriding the default filter
CxfHeaderFilterStrategy
instance by defining a new CxfHeaderFilterStrategy
bean and associating it with a CXF endpoint.
Sample relayHeaders configuration
relayHeaders
option to create a CxfHeaderFilterStrategy
bean that blocks all message headers. The CXF endpoints in the route use the headerFilterStrategy
option to install the filter strategy in the endpoint, where the headerFilterStrategy
setting has the syntax, headerFilterStrategy=#BeanID
.
<beans ...> ... <bean id="dropAllMessageHeadersStrategy" class="org.apache.camel.component.cxf.common.header.CxfHeaderFilterStrategy"> <!-- Set relayHeaders to false to drop all SOAP headers --> <property name="relayHeaders" value="false"/> </bean> <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="cxf:bean:routerNoRelayEndpoint?headerFilterStrategy=#dropAllMessageHeadersStrategy"/> <to uri="cxf:bean:serviceNoRelayEndpoint?headerFilterStrategy=#dropAllMessageHeadersStrategy"/> </route> </camelContext> ... </beans>
relayAllMessageHeaders option
relayAllMessageHeaders
option is used to propagate all SOAP headers, without applying any filtering (any installed filters would be bypassed). In order to enable this feature, you must set both relayHeaders
and relayAllMessageHeaders
to true
.
Sample relayAllMessageHeaders configuration
propagateAllMessages
filter strategy sets both relayHeaders
and relayAllMessageHeaders
to true
.
<beans ...> ... <bean id="propagateAllMessages" class="org.apache.camel.component.cxf.common.header.CxfHeaderFilterStrategy"> <!-- Set both properties to true to propagate *all* SOAP headers --> <property name="relayHeaders" value="true"/> <property name="relayAllMessageHeaders" value="true"/> </bean> <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="cxf:bean:routerNoRelayEndpoint?headerFilterStrategy=#propagateAllMessages"/> <to uri="cxf:bean:serviceNoRelayEndpoint?headerFilterStrategy=#propagateAllMessages"/> </route> </camelContext> ... </beans>
41.2. Header Filtering
Overview
CxfHeaderFilterStrategy
instance. The filtering mechanism then uses the header's XML namespace to lookup a particular filter, which it then applies to the header.
Filter map
CxfHeaderFilterStrategy
instance. For each filter that you install in CxfHeaderFilterStrategy
, corresponding entries are made in the filter map, where one or more XML schema namespaces are associated with each filter.
Figure 41.1. Filter Map
Filter behavior
PAYLOAD mode
POJO mode
41.3. Implementing a Custom Filter
Overview
MessageHeaderFilter
Java interface. You must associate a filter with one or more XML schema namespaces (representing the header's namespace) and it is possible to differentiate between request message headers and response message headers.
MessageHeaderFilter interface
MessageHeaderFilter
interface is defined in the org.apache.camel.component.cxf.common.header
package, as follows:
// Java package org.apache.camel.component.cxf.common.header; import java.util.List; import org.apache.camel.spi.HeaderFilterStrategy.Direction; import org.apache.cxf.headers.Header; public interface MessageHeaderFilter { List<String> getActivationNamespaces(); void filter(Direction direction, List<Header> headers); }
Implementing the filter() method
MessageHeaderFilter.filter()
method is reponsible for applying header filtering. Filtering is applied both before and after an operation is invoked on an endpoint. Hence, there are two directions to which filtering is applied, as follows:
Direction.OUT
- When the
direction
parameter equalsDirection.OUT
, the filter is being applied to a request either leaving a consumer endpoint or entering a producer endpoint (that is, it applies to a WS request message propagating through a route). Direction.IN
- When the
direction
parameter equalsDirection.IN
, the filter is being applied to a response either leaving a producer endpoint or entering a consumer endpoint (that is, it applies to a WS response message being sent back).
headers
. Any headers left in the list are propagated.
Binding filters to XML namespaces
getActivationNamespaces()
method, which returns the list of bound XML namespaces.
Identifying the namespace to bind to
Example 41.1. Sample Binding Namespaces
<wsdl:definitions targetNamespace="http://cxf.apache.org/schemas/cxf/idl/bank" xmlns:tns="http://cxf.apache.org/schemas/cxf/idl/bank" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"> ... <wsdl:binding name="BankSOAPBinding" type="tns:Bank"> <soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http" /> <wsdl:operation name="getAccount"> ... </wsdl:operation> ... </wsdl:binding> ... </wsdl>
soap:binding
tag, you can infer that namespace associated with the SOAP binding is http://schemas.xmlsoap.org/wsdl/soap/
.
Implementing a custom filter
MessageHeaderFilter
interface and implement its methods as described in this section. For example, Example 41.2, “Sample Header Filter Implementation” shows an example of a custom filter, CustomHeaderFilter
, that binds to the namespace, http://cxf.apache.org/bindings/custom
, and relays all of the headers that pass through it.
Example 41.2. Sample Header Filter Implementation
// Java package org.apache.camel.component.cxf.soap.headers; import java.util.Arrays; import java.util.List; import org.apache.camel.component.cxf.common.header.MessageHeaderFilter; import org.apache.camel.spi.HeaderFilterStrategy.Direction; import org.apache.cxf.headers.Header; public class CustomHeaderFilter implements MessageHeaderFilter { public static final String ACTIVATION_NAMESPACE = "http://cxf.apache.org/bindings/custom"; public static final List<String> ACTIVATION_NAMESPACES = Arrays.asList(ACTIVATION_NAMESPACE); public List<String> getActivationNamespaces() { return ACTIVATION_NAMESPACES; } public void filter(Direction direction, List<Header> headers) { } }
41.4. Installing Filters
Overview
messageHeaderFilters
property of the CxfHeaderFilterStrategy
object. When you initialize this property with a list of message header filters, the header filter strategy combines the specified filters to make a filter map.
messageHeaderFilters
property is of type, List<MessageHeaderFilter>
.
Installing filters in XML
CxfHeaderFilterStrategy
instance, specifying a customized list of header filters in the messageHeaderFilters
property. There are two header filters in this example: SoapMessageHeaderFilter
and CustomHeaderFilter
.
<bean id="customMessageFilterStrategy" class="org.apache.camel.component.cxf.common.header.CxfHeaderFilterStrategy"> <property name="messageHeaderFilters"> <list> <!-- SoapMessageHeaderFilter is the built in filter. It can be removed by omitting it. --> <bean class="org.apache.camel.component.cxf.common.header.SoapMessageHeaderFilter"/> <!-- Add custom filter here --> <bean class="org.apache.camel.component.cxf.soap.headers.CustomHeaderFilter"/> </list> </property> <!-- The 'relayHeaders' property is 'true' by default --> </bean>
SoapMessageHeaderFilter
SoapMessageHeaderFilter
filter, which is the default header filter. This filter is designed to filter standard SOAP headers and is bound to the following XML namespaces:
http://schemas.xmlsoap.org/soap/ http://schemas.xmlsoap.org/wsdl/soap/ http://schemas.xmlsoap.org/wsdl/soap12/
soap:actor
attribute (SOAP 1.1) or the soap:role
attribute (SOAP 1.2) is present and has the value next, the header is removed from the message. Otherwise, the header is propagated.
Namespace clashes
allowFilterNamespaceClash
property to true
in the CxfHeaderFilterStrategy
instance. When this policy is set to true
, the nearest to last filter is selected, in the event of a namespace clash.
Part IV. Programming EIP Components
Abstract
Chapter 42. Understanding Message Formats
Abstract
42.1. Exchanges
Overview
Figure 42.1. Exchange Object Passing through a Route
Processor.process()
method. This means that the exchange object is directly accessible to the source endpoint, the target endpoint, and all of the processors in between.
The Exchange interface
org.apache.camel.Exchange
interface defines methods to access In and Out messages, as shown in Example 42.1, “Exchange Methods”.
Example 42.1. Exchange Methods
// Access the In message Message getIn(); void setIn(Message in); // Access the Out message (if any) Message getOut(); void setOut(Message out); boolean hasOut(); // Access the exchange ID String getExchangeId(); void setExchangeId(String id);
Exchange
interface, see Section 51.1, “The Exchange Interface”.
Lazy creation of messages
getIn()
or getOut()
). The lazy message creation semantics are implemented by the org.apache.camel.impl.DefaultExchange
class.
getIn()
or getOut()
), or if you call an accessor with the boolean argument equal to true
(that is, getIn(true)
or getOut(true)
), the default method implementation creates a new message instance, if one does not already exist.
false
(that is, getIn(false)
or getOut(false)
), the default method implementation returns the current message value.[2]
Lazy creation of exchange IDs
getExchangeId()
on any exchange to obtain a unique ID for that exchange instance, but the ID is generated only when you actually call the method. The DefaultExchange.getExchangeId()
implementation of this method delegates ID generation to the UUID generator that is registered with the CamelContext
.
CamelContext
, see Section 42.4, “Built-In UUID Generators”.
42.2. Messages
Overview
- Message body
- Message headers
- Message attachments
Object
) and the message attachments are declared to be of type javax.activation.DataHandler
, which can contain arbitrary MIME types. If you need to obtain a concrete representation of the message contents, you can convert the body and headers to another type using the type converter mechanism and, possibly, using the marshalling and unmarshalling mechanism.
The Message interface
org.apache.camel.Message
interface defines methods to access the message body, message headers and message attachments, as shown in Example 42.2, “Message Interface”.
Example 42.2. Message Interface
// Access the message body Object getBody(); <T> T getBody(Class<T> type); void setBody(Object body); <T> void setBody(Object body, Class<T> type); // Access message headers Object getHeader(String name); <T> T getHeader(String name, Class<T> type); void setHeader(String name, Object value); Object removeHeader(String name); Map<String, Object> getHeaders(); void setHeaders(Map<String, Object> headers); // Access message attachments javax.activation.DataHandler getAttachment(String id); java.util.Map<String, javax.activation.DataHandler> getAttachments(); java.util.Set<String> getAttachmentNames(); void addAttachment(String id, javax.activation.DataHandler content) // Access the message ID String getMessageId(); void setMessageId(String messageId);
Message
interface, see Section 52.1, “The Message Interface”.
Lazy creation of bodies, headers, and attachments
foo
message header from the In message:
from("SourceURL") .filter(header("foo") .isEqualTo("bar")) .to("TargetURL");
header("foo")
call is executed. At that point, the underlying message implementation parses the headers and populates the header map. The message body is not parsed until you reach the end of the route, at the to("TargetURL")
call. At that point, the body is converted into the format required for writing it to the target endpoint, TargetURL.
Lazy creation of message IDs
getMessageId()
method. The DefaultExchange.getExchangeId()
implementation of this method delegates ID generation to the UUID generator that is registered with the CamelContext
.
getMessageId()
method implicitly, if the endpoint implements a protocol that requires a unique message ID. In particular, JMS messages normally include a header containing unique message ID, so the JMS component automatically calls getMessageId()
to obtain the message ID (this is controlled by the messageIdEnabled
option on the JMS endpoint).
CamelContext
, see Section 42.4, “Built-In UUID Generators”.
Initial message format
byte[]
, ByteBuffer
, InputStream
, or OutputStream
. This ensures that the overhead required for creating the initial message is minimal. Where more elaborate message formats are required components usually rely on type converters or marshalling processors.
Type converters
convertBodyTo(Class type)
method can be inserted into a route to convert the body of an In message, as follows:
from("SourceURL").convertBodyTo(String.class).to("TargetURL");
java.lang.String
. The following example shows how to append a string to the end of the In message body:
from("SourceURL").setBody(bodyAs(String.class).append("My Special Signature")).to("TargetURL");
from("SourceURL").setBody(body().append("My Special Signature")).to("TargetURL");
append()
method automatically converts the message body to a string before appending its argument.
Type conversion methods in Message
org.apache.camel.Message
interface exposes some methods that perform type conversion explicitly:
getBody(Class<T> type)
—Returns the message body as type,T
.getHeader(String name, Class<T> type)
—Returns the named header value as type,T
.
Converting to XML
byte[]
, ByteBuffer
, String
, and so on), the built-in type converter also supports conversion to XML formats. For example, you can convert a message body to the org.w3c.dom.Document
type. This conversion is more expensive than the simple conversions, because it involves parsing the entire message and then creating a tree of nodes to represent the XML document structure. You can convert to the following XML document types:
org.w3c.dom.Document
javax.xml.transform.sax.SAXSource
Marshalling and unmarshalling
marshal()
unmarshal()
Example 42.3. Unmarshalling a Java Object
from("file://tmp/appfiles/serialized") .unmarshal() .serialization() .<FurtherProcessing> .to("TargetURL");
Final message format
byte[]
array to an InputStream
type.
42.3. Built-In Type Converters
Overview
Message.getBody(Class<T> type)
or Message.getHeader(String name, Class<T> type)
. It is also possible to invoke the master type converter directly. For example, if you have an exchange object, exchange
, you could convert a given value to a String
as shown in Example 42.4, “Converting a Value to a String”.
Example 42.4. Converting a Value to a String
org.apache.camel.TypeConverter tc = exchange.getContext().getTypeConverter(); String str_value = tc.convertTo(String.class, value);
Basic type converters
java.io.File
String
byte[]
andjava.nio.ByteBuffer
java.io.InputStream
andjava.io.OutputStream
java.io.Reader
andjava.io.Writer
java.io.BufferedReader
andjava.io.BufferedWriter
java.io.StringReader
File
and String
types. The File
type can be converted to any of the preceding types, except Reader
, Writer
, and StringReader
. The String
type can be converted to File
, byte[]
, ByteBuffer
, InputStream
, or StringReader
. The conversion from String
to File
works by interpreting the string as a file name. The trio of String
, byte[]
, and ByteBuffer
are completely inter-convertible.
byte[]
to String
and from String
to byte[]
by setting the Exchange.CHARSET_NAME
exchange property in the current exchange. For example, to perform conversions using the UTF-8 character encoding, call exchange.setProperty("Exchange.CHARSET_NAME", "UTF-8")
. The supported character sets are described in the java.nio.charset.Charset
class.
Collection type converters
Object[]
java.util.Set
java.util.List
Map type converters
java.util.Map
java.util.HashMap
java.util.Hashtable
java.util.Properties
java.util.Set
type, where the set elements are of the MapEntry<K,V>
type.
DOM type converters
org.w3c.dom.Document
—convertible frombyte[]
,String
,java.io.File
, andjava.io.InputStream
.org.w3c.dom.Node
javax.xml.transform.dom.DOMSource
—convertible fromString
.javax.xml.transform.Source
—convertible frombyte[]
andString
.
SAX type converters
javax.xml.transform.sax.SAXSource
type, which supports the SAX event-driven XML parser (see the SAX Web site for details). You can convert to SAXSource
from the following types:
String
InputStream
Source
StreamSource
DOMSource
enum type converter
String
to enum
type conversions, where the string value is converted to the matching enum
constant from the specified enumeration class (the matching is case-insensitive). This type converter is rarely needed for converting message bodies, but it is frequently used internally by Apache Camel to select particular options.
INFO
, is converted into an enum
constant:
<to uri="log:foo?level=INFO"/>
enum
type converter is case-insensitive, any of the following alternatives would also work:
<to uri="log:foo?level=info"/> <to uri="log:foo?level=INfo"/> <to uri="log:foo?level=InFo"/>
Custom type converters
42.4. Built-In UUID Generators
Overview
CamelContext
. This UUID generator is then used whenever Apache Camel needs to generate a unique ID—in particular, the registered UUID generator is called to generate the IDs returned by the Exchange.getExchangeId()
and the Message.getMessageId()
methods.
SimpleUuidGenerator
) for testing purposes.
Provided UUID generators
org.apache.camel.impl.ActiveMQUuidGenerator
—(Default) generates the same style of ID as is used by Apache ActiveMQ. This implementation might not be suitable for all applications, because it uses some JDK APIs that are forbidden in the context of cloud computing (such as the Google App Engine).org.apache.camel.impl.SimpleUuidGenerator
—implements a simple counter ID, starting at1
. The underlying implementation uses thejava.util.concurrent.atomic.AtomicLong
type, so that it is thread-safe.org.apache.camel.impl.JavaUuidGenerator
—implements an ID based on thejava.util.UUID
type. Becausejava.util.UUID
is synchronized, this might affect performance on some highly concurrent systems.
Custom UUID generator
org.apache.camel.spi.UuidGenerator
interface, which is shown in Example 42.5, “UuidGenerator Interface”. The generateUuid()
must be implemented to return a unique ID string.
Example 42.5. UuidGenerator Interface
// Java package org.apache.camel.spi; /** * Generator to generate UUID strings. */ public interface UuidGenerator { String generateUuid(); }
Specifying the UUID generator using Java
setUuidGenerator()
method on the current CamelContext
object. For example, you can register a SimpleUuidGenerator
instance with the current CamelContext
, as follows:
// Java getContext().setUuidGenerator(new org.apache.camel.impl.SimpleUuidGenerator());
setUuidGenerator()
method should be called during startup, before any routes are activated.
Specifying the UUID generator using Spring
bean
element. When a camelContext
instance is created, it automatically looks up the Spring registry, searching for a bean that implements org.apache.camel.spi.UuidGenerator
. For example, you can register a SimpleUuidGenerator
instance with the CamelContext
as follows:
<beans ...> <bean id="simpleUuidGenerator" class="org.apache.camel.impl.SimpleUuidGenerator" /> <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> ... </camelContext> ... </beans>
Chapter 43. Implementing a Processor
Abstract
43.1. Processing Model
Pipelining model
Figure 43.1. Pipelining Model
ProcessorA
, ProcessorB
, and a producer endpoint, TargetURI.
Example 43.1. Java DSL Pipeline
from(SourceURI).pipeline(ProcessorA, ProcessorB, TargetURI);
43.2. Implementing a Simple Processor
Overview
Processor interface
org.apache.camel.Processor
interface. As shown in Example 43.2, “Processor Interface”, the interface defines a single method, process()
, which processes an exchange object.
Example 43.2. Processor Interface
package org.apache.camel; public interface Processor { void process(Exchange exchange) throws Exception; }
Implementing the Processor interface
Processor
interface and provide the logic for the process()
method. Example 43.3, “Simple Processor Implementation” shows the outline of a simple processor implementation.
Example 43.3. Simple Processor Implementation
import org.apache.camel.Processor; public class MyProcessor implements Processor { public MyProcessor() { } public void process(Exchange exchange) throws Exception { // Insert code that gets executed *before* delegating // to the next processor in the chain. ... } }
process()
method gets executed before the exchange object is delegated to the next processor in the chain.
Inserting the simple processor into a route
process()
DSL command to insert a simple processor into a route. Create an instance of your custom processor and then pass this instance as an argument to the process()
method, as follows:
org.apache.camel.Processor myProc = new MyProcessor(); from("SourceURL").process(myProc).to("TargetURL");
43.3. Accessing Message Content
Accessing message headers
Exchange.getIn()
), and then use the Message
interface to retrieve the individual headers (for example, using Message.getHeader()
).
Authorization
. This example uses the ExchangeHelper.getMandatoryHeader()
method, which eliminates the need to test for a null header value.
Example 43.4. Accessing an Authorization Header
import org.apache.camel.*;
import org.apache.camel.util.ExchangeHelper;
public class MyProcessor implements Processor {
public void process(Exchange exchange) {
String auth = ExchangeHelper.getMandatoryHeader(
exchange,
"Authorization",
String.class
);
// process the authorization string...
// ...
}
}
Message
interface, see Section 42.2, “Messages”.
Accessing the message body
Example 43.5. Accessing the Message Body
import org.apache.camel.*; import org.apache.camel.util.ExchangeHelper; public class MyProcessor implements Processor { public void process(Exchange exchange) { Message in = exchange.getIn(); in.setBody(in.getBody(String.class) + " World!"); } }
Accessing message attachments
Message.getAttachment()
method or the Message.getAttachments()
method. See Example 42.2, “Message Interface” for more details.
43.4. The ExchangeHelper Class
Overview
org.apache.camel.util.ExchangeHelper
class is a Apache Camel utility class that provides methods that are useful when implementing a processor.
Resolve an endpoint
resolveEndpoint()
method is one of the most useful methods in the ExchangeHelper
class. You use it inside a processor to create new Endpoint
instances on the fly.
Example 43.6. The resolveEndpoint()
Method
public final class ExchangeHelper { ... @SuppressWarnings({"unchecked" }) public static Endpoint resolveEndpoint(Exchange exchange, Object value) throws NoSuchEndpointException { ... } ... }
resolveEndpoint()
is an exchange instance, and the second argument is usually an endpoint URI string. Example 43.7, “Creating a File Endpoint” shows how to create a new file endpoint from an exchange instance exchange
Example 43.7. Creating a File Endpoint
Endpoint file_endp = ExchangeHelper.resolveEndpoint(exchange, "file://tmp/messages/in.xml");
Wrapping the exchange accessors
ExchangeHelper
class provides several static methods of the form getMandatoryBeanProperty()
, which wrap the corresponding getBeanProperty()
methods on the Exchange
class. The difference between them is that the original getBeanProperty()
accessors return null
, if the corresponding property is unavailable, and the getMandatoryBeanProperty()
wrapper methods throw a Java exception. The following wrapper methods are implemented in the ExchangeHelper
class:
public final class ExchangeHelper { ... public static <T> T getMandatoryProperty(Exchange exchange, String propertyName, Class<T> type) throws NoSuchPropertyException { ... } public static <T> T getMandatoryHeader(Exchange exchange, String propertyName, Class<T> type) throws NoSuchHeaderException { ... } public static Object getMandatoryInBody(Exchange exchange) throws InvalidPayloadException { ... } public static <T> T getMandatoryInBody(Exchange exchange, Class<T> type) throws InvalidPayloadException { ... } public static Object getMandatoryOutBody(Exchange exchange) throws InvalidPayloadException { ... } public static <T> T getMandatoryOutBody(Exchange exchange, Class<T> type) throws InvalidPayloadException { ... } ... }
Testing the exchange pattern
ExchangeHelper
class provides the following methods:
public final class ExchangeHelper { ... public static boolean isInCapable(Exchange exchange) { ... } public static boolean isOutCapable(Exchange exchange) { ... } ... }
Get the In message's MIME content type
ExchangeHelper.getContentType(exchange)
method. To implement this, the ExchangeHelper
object looks up the value of the In message's Content-Type
header—this method relies on the underlying component to populate the header value).
Chapter 44. Type Converters
Abstract
44.1. Type Converter Architecture
Overview
Type converter interface
org.apache.camel.TypeConverter
interface, which all type converters must implement.
Example 44.1. TypeConverter Interface
package org.apache.camel; public interface TypeConverter { <T> T convertTo(Class<T> type, Object value); }
Master type converter
CamelContext
object. To obtain a reference to the master type converter, you call the CamelContext.getTypeConverter()
method. For example, if you have an exchange object, exchange
, you can obtain a reference to the master type converter as shown in Example 44.2, “Getting a Master Type Converter”.
Example 44.2. Getting a Master Type Converter
org.apache.camel.TypeConverter tc = exchange.getContext().getTypeConverter();
Type converter loader
TypeConverterLoader
interface. Apache Camel currently uses only one kind of type converter loader—the annotation type converter loader (of AnnotationTypeConverterLoader
type).
Type conversion process
value
, to a specified type, toType
.
Figure 44.1. Type Conversion Process
- The
CamelContext
object holds a reference to the masterTypeConverter
instance. The first step in the conversion process is to retrieve the master type converter by callingCamelContext.getTypeConverter()
. - Type conversion is initiated by calling the
convertTo()
method on the master type converter. This method instructs the type converter to convert the data object,value
, from its original type to the type specified by thetoType
argument. - Because the master type converter is a front end for many different slave type converters, it looks up the appropriate slave type converter by checking a registry of type mappings The registry of type converters is keyed by a type mapping pair
(toType, fromType)
. If a suitable type converter is found in the registry, the master type converter calls the slave'sconvertTo()
method and returns the result. - If a suitable type converter cannot be found in the registry, the master type converter loads a new type converter, using the type converter loader.
- The type converter loader searches the available JAR libraries on the classpath to find a suitable type converter. Currently, the loader strategy that is used is implemented by the annotation type converter loader, which attempts to load a class annotated by the
org.apache.camel.Converter
annotation. See the section called “Create a TypeConverter file”. - If the type converter loader is successful, a new slave type converter is loaded and entered into the type converter registry. This type converter is then used to convert the
value
argument to thetoType
type. - If the data is successfully converted, the converted data value is returned. If the conversion does not succeed,
null
is returned.
44.2. Implementing Type Converter Using Annotations
Overview
How to implement a type converter
Implement an annotated converter class
@Converter
annotation. You must annotate the class itself and each of the static
methods intended to perform type conversion. Each converter method takes an argument that defines the from type, optionally takes a second Exchange
argument, and has a non-void return value that defines the to type. The type converter loader uses Java reflection to find the annotated methods and integrate them into the type converter mechanism. Example 44.3, “Example of an Annotated Converter Class” shows an example of an annotated converter class that defines a converter method for converting from java.io.File
to java.io.InputStream
and another converter method (with an Exchange
argument) for converting from byte[]
to String
.
Example 44.3. Example of an Annotated Converter Class
package com.YourDomain.YourPackageName; import org.apache.camel.Converter; import java.io.*; @Converter public class IOConverter { private IOConverter() { } @Converter public static InputStream toInputStream(File file) throws FileNotFoundException { return new BufferedInputStream(new FileInputStream(file)); } @Converter public static String toString(byte[] data, Exchange exchange) { if (exchange != null) { String charsetName = exchange.getProperty(Exchange.CHARSET_NAME, String.class); if (charsetName != null) { try { return new String(data, charsetName); } catch (UnsupportedEncodingException e) { LOG.warn("Can't convert the byte to String with the charset " + charsetName, e); } } } return new String(data); } }
toInputStream()
method is responsible for performing the conversion from the File
type to the InputStream
type and the toString()
method is responsible for performing the conversion from the byte[]
type to the String
type.
@Converter
annotation.
Create a TypeConverter file
TypeConverter
file at the following location:
META-INF/services/org/apache/camel/TypeConverter
TypeConverter
file must contain a comma-separated list of package names identifying the packages that contain type converter classes. For example, if you want the type converter loader to search the com.
YourDomain.
YourPackageName package for annotated converter classes, the TypeConverter
file would have the following contents:
com.YourDomain.YourPackageName
Package the type converter
META-INF
directory. Put this JAR file on your classpath to make it available to your Apache Camel application.
Fallback converter method
@Converter
annotation, you can optionally define a fallback converter method using the @FallbackConverter
annotation. The fallback converter method will only be tried, if the master type converter fails to find a regular converter method in the type registry.
byte[]
to String
), a fallback converter can potentially perform conversion between any pair of types. It is up to the code in the body of the fallback converter method to figure out which conversions it is able to perform. At run time, if a conversion cannot be performed by a regular converter, the master type converter iterates through every available fallback converter until it finds one that can perform the conversion.
// 1. Non-generic form of signature @FallbackConverter public static Object MethodName( Class type, Exchange exchange, Object value, TypeConverterRegistry registry ) // 2. Templating form of signature @FallbackConverter public static <T> T MethodName( Class<T> type, Exchange exchange, Object value, TypeConverterRegistry registry )
GenericFile
object, exploiting the type converters already available in the type converter registry:
package org.apache.camel.component.file; import org.apache.camel.Converter; import org.apache.camel.FallbackConverter; import org.apache.camel.Exchange; import org.apache.camel.TypeConverter; import org.apache.camel.spi.TypeConverterRegistry; @Converter public final class GenericFileConverter { private GenericFileConverter() { // Helper Class } @FallbackConverter public static <T> T convertTo(Class<T> type, Exchange exchange, Object value, TypeConverterRegistry registry) { // use a fallback type converter so we can convert the embedded body if the value is GenericFile if (GenericFile.class.isAssignableFrom(value.getClass())) { GenericFile file = (GenericFile) value; Class from = file.getBody().getClass(); TypeConverter tc = registry.lookup(type, from); if (tc != null) { Object body = file.getBody(); return tc.convertTo(type, exchange, body); } } return null; } ... }
44.3. Implementing a Type Converter Directly
Overview
Implement the TypeConverter interface
TypeConverter
interface. For example, the following MyOrderTypeConverter
class converts an integer value to a MyOrder
object, where the integer value is used to initialize the order ID in the MyOrder
object.
import org.apache.camel.TypeConverter private class MyOrderTypeConverter implements TypeConverter { public <T> T convertTo(Class<T> type, Object value) { // converter from value to the MyOrder bean MyOrder order = new MyOrder(); order.setId(Integer.parseInt(value.toString())); return (T) order; } public <T> T convertTo(Class<T> type, Exchange exchange, Object value) { // this method with the Exchange parameter will be preferd by Camel to invoke // this allows you to fetch information from the exchange during convertions // such as an encoding parameter or the likes return convertTo(type, value); } public <T> T mandatoryConvertTo(Class<T> type, Object value) { return convertTo(type, value); } public <T> T mandatoryConvertTo(Class<T> type, Exchange exchange, Object value) { return convertTo(type, value); } }
Add the type converter to the registry
// Add the custom type converter to the type converter registry context.getTypeConverterRegistry().addTypeConverter(MyOrder.class, String.class, new MyOrderTypeConverter());
context
is the current org.apache.camel.CamelContext
instance. The addTypeConverter()
method registers the MyOrderTypeConverter
class against the specific type conversion, from String.class
to MyOrder.class
.
Chapter 45. Producer and Consumer Templates
Abstract
45.1. Using the Producer Template
45.1.1. Introduction to the Producer Template
Overview
Exchange
object, as a message body, as a message body with a single header setting, and so on) and there are methods to support both the synchronous and the asynchronous style of invocation. Overall, producer template methods can be grouped into the following categories:
Synchronous invocation
sendSuffix()
and requestSuffix()
. For example, the methods for invoking an endpoint using either the default message exchange pattern (MEP) or an explicitly specified MEP are named send()
, sendBody()
, and sendBodyAndHeader()
(where these methods respectively send an Exchange
object, a message body, or a message body and header value). If you want to force the MEP to be InOut (request/reply semantics), you can call the request()
, requestBody()
, and requestBodyAndHeader()
methods instead.
ProducerTemplate
instance and use it to send a message body to the activemq:MyQueue
endpoint. The example also shows how to send a message body and header value using sendBodyAndHeader()
.
import org.apache.camel.ProducerTemplate import org.apache.camel.impl.DefaultProducerTemplate ... ProducerTemplate template = context.createProducerTemplate(); // Send to a specific queue template.sendBody("activemq:MyQueue", "<hello>world!</hello>"); // Send with a body and header template.sendBodyAndHeader( "activemq:MyQueue", "<hello>world!</hello>", "CustomerRating", "Gold" );
Synchronous invocation with a processor
send()
method with a Processor
argument instead of an Exchange
argument. In this case, the producer template implicitly asks the specified endpoint to create an Exchange
instance (typically, but not always having the InOnly MEP by default). This default exchange is then passed to the processor, which initializes the contents of the exchange object.
MyProcessor
processor to the activemq:MyQueue
endpoint.
import org.apache.camel.ProducerTemplate import org.apache.camel.impl.DefaultProducerTemplate ... ProducerTemplate template = context.createProducerTemplate(); // Send to a specific queue, using a processor to initialize template.send("activemq:MyQueue", new MyProcessor());
MyProcessor
class is implemented as shown in the following example. In addition to setting the In message body (as shown here), you could also initialize message heades and exchange properties.
import org.apache.camel.Processor; import org.apache.camel.Exchange; ... public class MyProcessor implements Processor { public MyProcessor() { } public void process(Exchange ex) { ex.getIn().setBody("<hello>world!</hello>"); } }
Asynchronous invocation
asyncSendSuffix()
and asyncRequestSuffix()
. For example, the methods for invoking an endpoint using either the default message exchange pattern (MEP) or an explicitly specified MEP are named asyncSend()
and asyncSendBody()
(where these methods respectively send an Exchange
object or a message body). If you want to force the MEP to be InOut (request/reply semantics), you can call the asyncRequestBody()
, asyncRequestBodyAndHeader()
, and asyncRequestBodyAndHeaders()
methods instead.
direct:start
endpoint. The asyncSend()
method returns a java.util.concurrent.Future
object, which is used to retrieve the invocation result at a later time.
import java.util.concurrent.Future; import org.apache.camel.Exchange; import org.apache.camel.impl.DefaultExchange; ... Exchange exchange = new DefaultExchange(context); exchange.getIn().setBody("Hello"); Future<Exchange> future = template.asyncSend("direct:start", exchange); // You can do other things, whilst waiting for the invocation to complete ... // Now, retrieve the resulting exchange from the Future Exchange result = future.get();
asyncSendBody()
or asyncRequestBody()
). In this case, you can use one of the following helper methods to extract the returned message body from the Future
object:
<T> T extractFutureBody(Future future, Class<T> type); <T> T extractFutureBody(Future future, long timeout, TimeUnit unit, Class<T> type) throws TimeoutException;
extractFutureBody()
method blocks until the invocation completes and the reply message is available. The second version of the extractFutureBody()
method allows you to specify a timeout. Both methods have a type argument, type
, which casts the returned message body to the specified type using a built-in type converter.
asyncRequestBody()
method to send a message body to the direct:start
endpoint. The blocking extractFutureBody()
method is then used to retrieve the reply message body from the Future
object.
Future<Object> future = template.asyncRequestBody("direct:start", "Hello"); // You can do other things, whilst waiting for the invocation to complete ... // Now, retrieve the reply message body as a String type String result = template.extractFutureBody(future, String.class);
Asynchronous invocation with a callback
asyncCallback()
, asyncCallbackSendBody()
, or asyncCallbackRequestBody()
methods. In this case, you supply a callback object (of org.apache.camel.impl.SynchronizationAdapter
type), which automatically gets invoked in the sub-thread as soon as a reply message arrives.
Synchronization
callback interface is defined as follows:
package org.apache.camel.spi;
import org.apache.camel.Exchange;
public interface Synchronization {
void onComplete(Exchange exchange);
void onFailure(Exchange exchange);
}
onComplete()
method is called on receipt of a normal reply and the onFailure()
method is called on receipt of a fault message reply. Only one of these methods gets called back, so you must override both of them to ensure that all types of reply are processed.
direct:start
endpoint, where the reply message is processed in the sub-thread by the SynchronizationAdapter
callback object.
import java.util.concurrent.Future; import java.util.concurrent.TimeUnit; import org.apache.camel.Exchange; import org.apache.camel.impl.DefaultExchange; import org.apache.camel.impl.SynchronizationAdapter; ... Exchange exchange = context.getEndpoint("direct:start").createExchange(); exchange.getIn().setBody("Hello"); Future<Exchange> future = template.asyncCallback("direct:start", exchange, new SynchronizationAdapter() { @Override public void onComplete(Exchange exchange) { assertEquals("Hello World", exchange.getIn().getBody()); } });
SynchronizationAdapter
class is a default implementation of the Synchronization
interface, which you can override to provide your own definitions of the onComplete()
and onFailure()
callback methods.
asyncCallback()
method also returns a Future
object—for example:
// Retrieve the reply from the main thread, specifying a timeout Exchange reply = future.get(10, TimeUnit.SECONDS);
45.1.2. Synchronous Send
Overview
Send an exchange
send()
method is a general-purpose method that sends the contents of an Exchange
object to an endpoint, using the message exchange pattern (MEP) of the exchange. The return value is the exchange that you get after it has been processed by the producer endpoint (possibly containing an Out message, depending on the MEP).
send()
method for sending an exchange that let you specify the target endpoint in one of the following ways: as the default endpoint, as an endpoint URI, or as an Endpoint
object.
Exchange send(Exchange exchange); Exchange send(String endpointUri, Exchange exchange); Exchange send(Endpoint endpoint, Exchange exchange);
Send an exchange populated by a processor
send()
method is to use a processor to populate a default exchange, instead of supplying the exchange object explicitly (see the section called “Synchronous invocation with a processor” for details).
send()
methods for sending an exchange populated by a processor let you specify the target endpoint in one of the following ways: as the default endpoint, as an endpoint URI, or as an Endpoint
object. In addition, you can optionally specify the exchange's MEP by supplying the pattern
argument, instead of accepting the default.
Exchange send(Processor processor); Exchange send(String endpointUri, Processor processor); Exchange send(Endpoint endpoint, Processor processor); Exchange send( String endpointUri, ExchangePattern pattern, Processor processor ); Exchange send( Endpoint endpoint, ExchangePattern pattern, Processor processor );
Send a message body
sendBody()
methods to provide the message body as an argument and let the producer template take care of inserting the body into a default exchange object.
sendBody()
methods let you specify the target endpoint in one of the following ways: as the default endpoint, as an endpoint URI, or as an Endpoint
object. In addition, you can optionally specify the exchange's MEP by supplying the pattern
argument, instead of accepting the default. The methods without a pattern
argument return void
(even though the invocation might give rise to a reply in some cases); and the methods with a pattern
argument return either the body of the Out message (if there is one) or the body of the In message (otherwise).
void sendBody(Object body); void sendBody(String endpointUri, Object body); void sendBody(Endpoint endpoint, Object body); Object sendBody( String endpointUri, ExchangePattern pattern, Object body ); Object sendBody( Endpoint endpoint, ExchangePattern pattern, Object body );
Send a message body and header(s)
sendBodyAndHeader()
methods are useful for this kind of header testing. You supply the message body and header setting as arguments to sendBodyAndHeader()
and let the producer template take care of inserting the body and header setting into a default exchange object.
sendBodyAndHeader()
methods let you specify the target endpoint in one of the following ways: as the default endpoint, as an endpoint URI, or as an Endpoint
object. In addition, you can optionally specify the exchange's MEP by supplying the pattern
argument, instead of accepting the default. The methods without a pattern
argument return void
(even though the invocation might give rise to a reply in some cases); and the methods with a pattern
argument return either the body of the Out message (if there is one) or the body of the In message (otherwise).
void sendBodyAndHeader( Object body, String header, Object headerValue ); void sendBodyAndHeader( String endpointUri, Object body, String header, Object headerValue ); void sendBodyAndHeader( Endpoint endpoint, Object body, String header, Object headerValue ); Object sendBodyAndHeader( String endpointUri, ExchangePattern pattern, Object body, String header, Object headerValue ); Object sendBodyAndHeader( Endpoint endpoint, ExchangePattern pattern, Object body, String header, Object headerValue );
sendBodyAndHeaders()
methods are similar to the sendBodyAndHeader()
methods, except that instead of supplying just a single header setting, these methods allow you to specify a complete hash map of header settings.
void sendBodyAndHeaders( Object body, Map<String, Object> headers ); void sendBodyAndHeaders( String endpointUri, Object body, Map<String, Object> headers ); void sendBodyAndHeaders( Endpoint endpoint, Object body, Map<String, Object> headers ); Object sendBodyAndHeaders( String endpointUri, ExchangePattern pattern, Object body, Map<String, Object> headers ); Object sendBodyAndHeaders( Endpoint endpoint, ExchangePattern pattern, Object body, Map<String, Object> headers );
Send a message body and exchange property
sendBodyAndProperty()
methods. You supply the message body and property setting as arguments to sendBodyAndProperty()
and let the producer template take care of inserting the body and exchange property into a default exchange object.
sendBodyAndProperty()
methods let you specify the target endpoint in one of the following ways: as the default endpoint, as an endpoint URI, or as an Endpoint
object. In addition, you can optionally specify the exchange's MEP by supplying the pattern
argument, instead of accepting the default. The methods without a pattern
argument return void
(even though the invocation might give rise to a reply in some cases); and the methods with a pattern
argument return either the body of the Out message (if there is one) or the body of the In message (otherwise).
void sendBodyAndProperty( Object body, String property, Object propertyValue ); void sendBodyAndProperty( String endpointUri, Object body, String property, Object propertyValue ); void sendBodyAndProperty( Endpoint endpoint, Object body, String property, Object propertyValue ); Object sendBodyAndProperty( String endpoint, ExchangePattern pattern, Object body, String property, Object propertyValue ); Object sendBodyAndProperty( Endpoint endpoint, ExchangePattern pattern, Object body, String property, Object propertyValue );
45.1.3. Synchronous Request with InOut Pattern
Overview
Request an exchange populated by a processor
request()
method is a general-purpose method that uses a processor to populate a default exchange and forces the message exchange pattern to be InOut (so that the invocation obeys request/reply semantics). The return value is the exchange that you get after it has been processed by the producer endpoint, where the Out message contains the reply message.
request()
methods for sending an exchange populated by a processor let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object.
Exchange request(String endpointUri, Processor processor); Exchange request(Endpoint endpoint, Processor processor);
Request a message body
requestBody()
methods to provide the request message body as an argument and let the producer template take care of inserting the body into a default exchange object.
requestBody()
methods let you specify the target endpoint in one of the following ways: as the default endpoint, as an endpoint URI, or as an Endpoint
object. The return value is the body of the reply message (Out message body), which can either be returned as plain Object
or converted to a specific type, T
, using the built-in type converters (see Section 42.3, “Built-In Type Converters”).
Object requestBody(Object body); <T> T requestBody(Object body, Class<T> type); Object requestBody( String endpointUri, Object body ); <T> T requestBody( String endpointUri, Object body, Class<T> type ); Object requestBody( Endpoint endpoint, Object body ); <T> T requestBody( Endpoint endpoint, Object body, Class<T> type );
Request a message body and header(s)
requestBodyAndHeader()
methods. You supply the message body and header setting as arguments to requestBodyAndHeader()
and let the producer template take care of inserting the body and exchange property into a default exchange object.
requestBodyAndHeader()
methods let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object. The return value is the body of the reply message (Out message body), which can either be returned as plain Object
or converted to a specific type, T
, using the built-in type converters (see Section 42.3, “Built-In Type Converters”).
Object requestBodyAndHeader( String endpointUri, Object body, String header, Object headerValue ); <T> T requestBodyAndHeader( String endpointUri, Object body, String header, Object headerValue, Class<T> type ); Object requestBodyAndHeader( Endpoint endpoint, Object body, String header, Object headerValue ); <T> T requestBodyAndHeader( Endpoint endpoint, Object body, String header, Object headerValue, Class<T> type );
requestBodyAndHeaders()
methods are similar to the requestBodyAndHeader()
methods, except that instead of supplying just a single header setting, these methods allow you to specify a complete hash map of header settings.
Object requestBodyAndHeaders( String endpointUri, Object body, Map<String, Object> headers ); <T> T requestBodyAndHeaders( String endpointUri, Object body, Map<String, Object> headers, Class<T> type ); Object requestBodyAndHeaders( Endpoint endpoint, Object body, Map<String, Object> headers ); <T> T requestBodyAndHeaders( Endpoint endpoint, Object body, Map<String, Object> headers, Class<T> type );
45.1.4. Asynchronous Send
Overview
Send an exchange
asyncSend()
method takes an Exchange
argument and invokes an endpoint asynchronously, using the message exchange pattern (MEP) of the specified exchange. The return value is a java.util.concurrent.Future
object, which is a ticket you can use to collect the reply message at a later time—for details of how to obtain the return value from the Future
object, see the section called “Asynchronous invocation”.
asyncSend()
methods let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object.
Future<Exchange> asyncSend(String endpointUri, Exchange exchange); Future<Exchange> asyncSend(Endpoint endpoint, Exchange exchange);
Send an exchange populated by a processor
asyncSend()
method is to use a processor to populate a default exchange, instead of supplying the exchange object explicitly.
asyncSend()
methods let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object.
Future<Exchange> asyncSend(String endpointUri, Processor processor); Future<Exchange> asyncSend(Endpoint endpoint, Processor processor);
Send a message body
asyncSendBody()
methods to send a message body asynchronously and let the producer template take care of inserting the body into a default exchange object.
asyncSendBody()
methods let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object.
Future<Object> asyncSendBody(String endpointUri, Object body); Future<Object> asyncSendBody(Endpoint endpoint, Object body);
45.1.5. Asynchronous Request with InOut Pattern
Overview
Request a message body
requestBody()
methods to provide the request message body as an argument and let the producer template take care of inserting the body into a default exchange object.
asyncRequestBody()
methods let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object. The return value that is retrievable from the Future
object is the body of the reply message (Out message body), which can be returned either as a plain Object
or converted to a specific type, T
, using a built-in type converter (see the section called “Asynchronous invocation”).
Future<Object> asyncRequestBody( String endpointUri, Object body ); <T> Future<T> asyncRequestBody( String endpointUri, Object body, Class<T> type ); Future<Object> asyncRequestBody( Endpoint endpoint, Object body ); <T> Future<T> asyncRequestBody( Endpoint endpoint, Object body, Class<T> type );
Request a message body and header(s)
asyncRequestBodyAndHeader()
methods. You supply the message body and header setting as arguments to asyncRequestBodyAndHeader()
and let the producer template take care of inserting the body and exchange property into a default exchange object.
asyncRequestBodyAndHeader()
methods let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object. The return value that is retrievable from the Future
object is the body of the reply message (Out message body), which can be returned either as a plain Object
or converted to a specific type, T
, using a built-in type converter (see the section called “Asynchronous invocation”).
Future<Object> asyncRequestBodyAndHeader( String endpointUri, Object body, String header, Object headerValue ); <T> Future<T> asyncRequestBodyAndHeader( String endpointUri, Object body, String header, Object headerValue, Class<T> type ); Future<Object> asyncRequestBodyAndHeader( Endpoint endpoint, Object body, String header, Object headerValue ); <T> Future<T> asyncRequestBodyAndHeader( Endpoint endpoint, Object body, String header, Object headerValue, Class<T> type );
asyncRequestBodyAndHeaders()
methods are similar to the asyncRequestBodyAndHeader()
methods, except that instead of supplying just a single header setting, these methods allow you to specify a complete hash map of header settings.
Future<Object> asyncRequestBodyAndHeaders( String endpointUri, Object body, Map<String, Object> headers ); <T> Future<T> asyncRequestBodyAndHeaders( String endpointUri, Object body, Map<String, Object> headers, Class<T> type ); Future<Object> asyncRequestBodyAndHeaders( Endpoint endpoint, Object body, Map<String, Object> headers ); <T> Future<T> asyncRequestBodyAndHeaders( Endpoint endpoint, Object body, Map<String, Object> headers, Class<T> type );
45.1.6. Asynchronous Send with Callback
Overview
Send an exchange
asyncCallback()
method takes an Exchange
argument and invokes an endpoint asynchronously, using the message exchange pattern (MEP) of the specified exchange. This method is similar to the asyncSend()
method for exchanges, except that it takes an additional org.apache.camel.spi.Synchronization
argument, which is a callback interface with two methods: onComplete()
and onFailure()
. For details of how to use the Synchronization
callback, see the section called “Asynchronous invocation with a callback”.
asyncCallback()
methods let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object.
Future<Exchange> asyncCallback( String endpointUri, Exchange exchange, Synchronization onCompletion ); Future<Exchange> asyncCallback( Endpoint endpoint, Exchange exchange, Synchronization onCompletion );
Send an exchange populated by a processor
asyncCallback()
method for processors calls a processor to populate a default exchange and forces the message exchange pattern to be InOut (so that the invocation obeys request/reply semantics).
asyncCallback()
methods let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object.
Future<Exchange> asyncCallback( String endpointUri, Processor processor, Synchronization onCompletion ); Future<Exchange> asyncCallback( Endpoint endpoint, Processor processor, Synchronization onCompletion );
Send a message body
asyncCallbackSendBody()
methods to send a message body asynchronously and let the producer template take care of inserting the body into a default exchange object.
asyncCallbackSendBody()
methods let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object.
Future<Object> asyncCallbackSendBody( String endpointUri, Object body, Synchronization onCompletion ); Future<Object> asyncCallbackSendBody( Endpoint endpoint, Object body, Synchronization onCompletion );
Request a message body
asyncCallbackRequestBody()
methods to provide the request message body as an argument and let the producer template take care of inserting the body into a default exchange object.
asyncCallbackRequestBody()
methods let you specify the target endpoint in one of the following ways: as an endpoint URI, or as an Endpoint
object.
Future<Object> asyncCallbackRequestBody( String endpointUri, Object body, Synchronization onCompletion ); Future<Object> asyncCallbackRequestBody( Endpoint endpoint, Object body, Synchronization onCompletion );
45.2. Using the Consumer Template
Overview
Example of polling exchanges
receive()
; receive()
with a timeout; or receiveNoWait()
, which returns immediately. Because a consumer endpoint represents a service, it is also essential to start the service thread by calling start()
before you attempt to poll for exchanges.
seda:foo
consumer endpoint using the blocking receive()
method:
import org.apache.camel.ProducerTemplate; import org.apache.camel.ConsumerTemplate; import org.apache.camel.Exchange; ... ProducerTemplate template = context.createProducerTemplate(); ConsumerTemplate consumer = context.createConsumerTemplate(); // Start the consumer service consumer.start(); ... template.sendBody("seda:foo", "Hello"); Exchange out = consumer.receive("seda:foo"); ... // Stop the consumer service consumer.stop();
consumer
, is instantiated using the CamelContext.createConsumerTemplate()
method and the consumer service thread is started by calling ConsumerTemplate.start()
.
Example of polling message bodies
receiveBody()
; receiveBody()
with a timeout; or receiveBodyNoWait()
, which returns immediately. As in the previous example, it is also essential to start the service thread by calling start()
before you attempt to poll for exchanges.
seda:foo
consumer endpoint using the blocking receiveBody()
method:
import org.apache.camel.ProducerTemplate; import org.apache.camel.ConsumerTemplate; ... ProducerTemplate template = context.createProducerTemplate(); ConsumerTemplate consumer = context.createConsumerTemplate(); // Start the consumer service consumer.start(); ... template.sendBody("seda:foo", "Hello"); Object body = consumer.receiveBody("seda:foo"); ... // Stop the consumer service consumer.stop();
Methods for polling exchanges
receive()
without a timeout blocks indefinitely; receive()
with a timeout blocks for the specified period of milliseconds; and receiveNoWait()
is non-blocking. You can specify the consumer endpoint either as an endpoint URI or as an Endpoint
instance.
Exchange receive(String endpointUri); Exchange receive(String endpointUri, long timeout); Exchange receiveNoWait(String endpointUri); Exchange receive(Endpoint endpoint); Exchange receive(Endpoint endpoint, long timeout); Exchange receiveNoWait(Endpoint endpoint);
Methods for polling message bodies
receiveBody()
without a timeout blocks indefinitely; receiveBody()
with a timeout blocks for the specified period of milliseconds; and receiveBodyNoWait()
is non-blocking. You can specify the consumer endpoint either as an endpoint URI or as an Endpoint
instance. Moreover, by calling the templating forms of these methods, you can convert the returned body to a particular type, T
, using a built-in type converter.
Object receiveBody(String endpointUri); Object receiveBody(String endpointUri, long timeout); Object receiveBodyNoWait(String endpointUri); Object receiveBody(Endpoint endpoint); Object receiveBody(Endpoint endpoint, long timeout); Object receiveBodyNoWait(Endpoint endpoint); <T> T receiveBody(String endpointUri, Class<T> type); <T> T receiveBody(String endpointUri, long timeout, Class<T> type); <T> T receiveBodyNoWait(String endpointUri, Class<T> type); <T> T receiveBody(Endpoint endpoint, Class<T> type); <T> T receiveBody(Endpoint endpoint, long timeout, Class<T> type); <T> T receiveBodyNoWait(Endpoint endpoint, Class<T> type);
Chapter 46. Implementing a Component
Abstract
46.1. Component Architecture
46.1.1. Factory Patterns for a Component
Overview
Component
object itself (an instance of org.apache.camel.Component
type). You can use the Component
object as a factory to create Endpoint
objects, which in turn act as factories for creating Consumer
, Producer
, and Exchange
objects. These relationships are summarized in Figure 46.1, “Component Factory Patterns”
Figure 46.1. Component Factory Patterns
Component
Component.createEndpoint()
method, which is responsible for creating new endpoints on demand.
Endpoint
org.apache.camel.Endpoint
interface. The Endpoint
interface defines the following factory methods:
createConsumer()
andcreatePollingConsumer()
—Creates a consumer endpoint, which represents the source endpoint at the beginning of a route.createProducer()
—Creates a producer endpoint, which represents the target endpoint at the end of a route.createExchange()
—Creates an exchange object, which encapsulates the messages passed up and down the route.
Consumer
org.apache.camel.Consumer
interface. There are a number of different patterns you can follow when implementing a consumer. These patterns are described in Section 46.1.3, “Consumer Patterns and Threading”.
Producer
org.apache.camel.Producer
interface. You can optionally implement the producer to support an asynchronous style of processing. See Section 46.1.4, “Asynchronous Processing” for details.
Exchange
org.apache.camel.Exchange
interface. The default implementation, DefaultExchange
, is sufficient for many component implementations. However, if you want to associated extra data with the exchanges or have the exchanges preform additional processing, it can be useful to customize the exchange implementation.
Message
Exchange
object:
- In message—holds the current message.
- Out message—temporarily holds a reply message.
org.apache.camel.Message
. It is not always necessary to customize the message implementation—the default implementation, DefaultMessage
, is usually adequate.
46.1.2. Using a Component in a Route
Overview
org.apache.camel.Processor
type. Messages are encapsulated in an exchange object, E
, which gets passed from node to node by invoking the process()
method. The architecture of the processor pipeline is illustrated in Figure 46.2, “Consumer and Producer Instances in a Route”.
Figure 46.2. Consumer and Producer Instances in a Route
Source endpoint
org.apache.camel.Consumer
object. The source endpoint is responsible for accepting incoming request messages and dispatching replies. When constructing the route, Apache Camel creates the appropriate Consumer
type based on the component prefix from the endpoint URI, as described in Section 46.1.1, “Factory Patterns for a Component”.
Processors
org.apache.camel.Processor
interface). You can insert either standard processors (for example, filter
, throttler
, or delayer
) or insert your own custom processor implementations.
Target endpoint
org.apache.camel.Producer
object. Because it comes at the end of a processor pipeline, the producer is also a processor object (implementing the org.apache.camel.Processor
interface). The target endpoint is responsible for sending outgoing request messages and receiving incoming replies. When constructing the route, Apache Camel creates the appropriate Producer
type based on the component prefix from the endpoint URI.
46.1.3. Consumer Patterns and Threading
Overview
- Event-driven pattern—The consumer is driven by an external thread.
- Scheduled poll pattern—The consumer is driven by a dedicated thread pool.
- Polling pattern—The threading model is left undefined.
Event-driven pattern
handleNotification()
method to initiate request processing—see Example 49.4, “JMXConsumer Implementation” for details.
notify()
method.
Figure 46.3. Event-Driven Consumer
- The consumer must implement a method to receive the incoming event (in Figure 46.3, “Event-Driven Consumer” this is represented by the
notify()
method). The thread that callsnotify()
is normally a separate part of the application, so the consumer's threading policy is externally driven.For example, in the case of the JMX consumer implementation, the consumer implements theNotificationListener.handleNotification()
method to receive notifications from JMX. The threads that drive the consumer processing are created within the JMX layer. - In the body of the
notify()
method, the consumer first converts the incoming event into an exchange object,E
, and then callsprocess()
on the next processor in the route, passing the exchange object as its argument.
Scheduled poll pattern
Figure 46.4. Scheduled Poll Consumer
- The scheduled executor service has a pool of threads at its disposal, that can be used to initiate consumer processing. After each scheduled time interval has elapsed, the scheduled executor service attempts to grab a free thread from its pool (there are five threads in the pool by default). If a free thread is available, it uses that thread to call the
poll()
method on the consumer. - The consumer's
poll()
method is intended to trigger processing of an incoming request. In the body of thepoll()
method, the consumer attempts to retrieve an incoming message. If no request is available, thepoll()
method returns immediately. - If a request message is available, the consumer inserts it into an exchange object and then calls
process()
on the next processor in the route, passing the exchange object as its argument.
Polling pattern
receive()
receiveNoWait()
receive(long timeout)
Figure 46.5. Polling Consumer
- Processing of an incoming request is initiated whenever one of the consumer's polling methods is called. The mechanism for calling these polling methods is implementation defined.
- In the body of the
receive()
method, the consumer attempts to retrieve an incoming request message. If no message is currently available, the behavior depends on which receive method was called.receiveNoWait()
returns immediatelyreceive(long timeout)
waits for the specified timeout interval[3] before returningreceive()
waits until a message is received
- If a request message is available, the consumer inserts it into an exchange object and then calls
process()
on the next processor in the route, passing the exchange object as its argument.
46.1.4. Asynchronous Processing
Overview
process()
on a producer, the process()
method blocks until a reply is received. In this case, the processor's thread remains blocked until the producer has completed the cycle of sending the request and receiving the reply.
process()
call does not block. In this case, you should implement the producer using an asynchronous pattern, which gives the preceding processor the option of invoking a non-blocking version of the process()
method.
Synchronous producer
Figure 46.6. Synchronous Producer
- The preceding processor in the pipeline calls the synchronous
process()
method on the producer to initiate synchronous processing. The synchronousprocess()
method takes a single exchange argument. - In the body of the
process()
method, the producer sends the request (In message) to the endpoint. - If required by the exchange pattern, the producer waits for the reply (Out message) to arrive from the endpoint. This step can cause the
process()
method to block indefinitely. However, if the exchange pattern does not mandate a reply, theprocess()
method can return immediately after sending the request. - When the
process()
method returns, the exchange object contains the reply from the synchronous call (an Out message message).
Asynchronous producer
Figure 46.7. Asynchronous Producer
- Before the processor can call the asynchronous
process()
method, it must create an asynchronous callback object, which is responsible for processing the exchange on the return portion of the route. For the asynchronous callback, the processor must implement a class that inherits from theAsyncCallback
interface. - The processor calls the asynchronous
process()
method on the producer to initiate asynchronous processing. The asynchronousprocess()
method takes two arguments:- an exchange object
- a synchronous callback object
- In the body of the
process()
method, the producer creates aRunnable
object that encapsulates the processing code. The producer then delegates the execution of thisRunnable
object to a sub-thread. - The asynchronous
process()
method returns, thereby freeing up the processor's thread. The exchange processing continues in a separate sub-thread. - The
Runnable
object sends the In message to the endpoint. - If required by the exchange pattern, the
Runnable
object waits for the reply (Out or Fault message) to arrive from the endpoint. TheRunnable
object remains blocked until the reply is received. - After the reply arrives, the
Runnable
object inserts the reply (Out message) into the exchange object and then callsdone()
on the asynchronous callback object. The asynchronous callback is then responsible for processing the reply message (executed in the sub-thread).
46.2. How to Implement a Component
Overview
Which interfaces do you need to implement?
org.apache.camel.Component
org.apache.camel.Endpoint
org.apache.camel.Consumer
org.apache.camel.Producer
org.apache.camel.Exchange
org.apache.camel.Message
Implementation steps
- Implement the
Component
interface—A component object acts as an endpoint factory. You extend theDefaultComponent
class and implement thecreateEndpoint()
method. - Implement the
Endpoint
interface—An endpoint represents a resource identified by a specific URI. The approach taken when implementing an endpoint depends on whether the consumers follow an event-driven pattern, a scheduled poll pattern, or a polling pattern.For an event-driven pattern, implement the endpoint by extending theDefaultEndpoint
class and implementing the following methods:createProducer()
createConsumer()
For a scheduled poll pattern, implement the endpoint by extending theScheduledPollEndpoint
class and implementing the following methods:createProducer()
createConsumer()
For a polling pattern, implement the endpoint by extending theDefaultPollingEndpoint
class and implementing the following methods:createProducer()
createPollConsumer()
- Implement the
Consumer
interface—There are several different approaches you can take to implementing a consumer, depending on which pattern you need to implement (event-driven, scheduled poll, or polling). The consumer implementation is also crucially important for determining the threading model used for processing a message exchange. - Implement the
Producer
interface—To implement a producer, you extend theDefaultProducer
class and implement theprocess()
method. - Optionally implement the Exchange or the Message interface—The default implementations of
Exchange
andMessage
can be used directly, but occasionally, you might find it necessary to customize these types.
Installing and configuring the component
- Add the component directly to the CamelContext—The
CamelContext.addComponent()
method adds a component programatically. - Add the component using Spring configuration—The standard Spring
bean
element creates a component instance. The bean'sid
attribute implicitly defines the component prefix. For details, see Section 46.3.2, “Configuring a Component”. - Configure Apache Camel to auto-discover the component—Auto-discovery, ensures that Apache Camel automatically loads the component on demand. For details, see Section 46.3.1, “Setting Up Auto-Discovery”.
46.3. Auto-Discovery and Configuration
46.3.1. Setting Up Auto-Discovery
Overview
Availability of component classes
Configuring auto-discovery
/META-INF/services/org/apache/camel/component/component-prefix
class=component-class-name
Example
/META-INF/services/org/apache/camel/component/ftp
class=org.apache.camel.component.file.remote.RemoteFileComponent
camel-ftp-
Version.jar
.
46.3.2. Configuring a Component
Overview
META-INF/spring/camel-context.xml
. To find the component, the component's URI prefix is matched against the ID attribute of a bean
element in the Spring configuration. If the component prefix matches a bean element ID, Apache Camel instantiates the referenced class and injects the properties specified in the Spring configuration.
Define bean properties on your component class
public class CustomComponent extends DefaultComponent<CustomExchange> { ... PropType getProperty() { ... } void setProperty(PropType v) { ... } }
getProperty()
method and the setProperty()
method access the value of property.
Configure the component in Spring
META-INF/spring/camel-context.xml
, as shown in Example 46.1, “Configuring a Component in Spring”.
Example 46.1. Configuring a Component in Spring
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd"> <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <package>RouteBuilderPackage</package> </camelContext> <bean id="component-prefix" class="component-class-name"> <property name="property" value="propertyValue"/> </bean> </beans>
bean
element with ID component-prefix configures the component-class-name component. You can inject properties into the component instance using property
elements. For example, the property
element in the preceding example would inject the value, propertyValue, into the property property by calling setProperty()
on the component.
Examples
jms
. These settings are added to the Spring configuration file, camel-context.xml
.
Example 46.2. JMS Component Spring Configuration
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd"> <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring"> <package>org.apache.camel.example.spring</package> 1 </camelContext> <bean id="jms" class="org.apache.camel.component.jms.JmsComponent"> 2 <property name="connectionFactory"> 3 <bean class="org.apache.activemq.ActiveMQConnectionFactory"> <property name="brokerURL" value="vm://localhost?broker.persistent=false&broker.useJmx=false"/> 4 </bean> </property> </bean> </beans>
- 1
- The
CamelContext
automatically instantiates anyRouteBuilder
classes that it finds in the specified Java package, org.apache.camel.example.spring. - 2
- The bean element with ID,
jms
, configures the JMS component. The bean ID corresponds to the component's URI prefix. For example, if a route specifies an endpoint with the URI, jms://MyQName, Apache Camel automatically loads the JMS component using the settings from thejms
bean element. - 3
- JMS is just a wrapper for a messaging service. You must specify the concrete implementation of the messaging system by setting the
connectionFactory
property on theJmsComponent
class. - 4
- In this example, the concrete implementation of the JMS messaging service is Apache ActiveMQ. The
brokerURL
property initializes a connection to an ActiveMQ broker instance, where the message broker is embedded in the local Java virtual machine (JVM). If a broker is not already present in the JVM, ActiveMQ will instantiate it with the optionsbroker.persistent=false
(the broker does not persist messages) andbroker.useJmx=false
(the broker does not open a JMX port).
Chapter 47. Component Interface
Abstract
Component
interface.
47.1. The Component Interface
Overview
org.apache.camel.Component
interface. An instance of Component
type provides the entry point into a custom component. That is, all of the other objects in a component are ultimately accessible through the Component
instance. Figure 47.1, “Component Inheritance Hierarchy” shows the relevant Java interfaces and classes that make up the Component
inheritance hierarchy.
Figure 47.1. Component Inheritance Hierarchy
The Component interface
org.apache.camel.Component
interface.
Example 47.1. Component Interface
package org.apache.camel; public interface Component { CamelContext getCamelContext(); void setCamelContext(CamelContext context); Endpoint createEndpoint(String uri) throws Exception; }
Component methods
Component
interface defines the following methods:
getCamelContext()
andsetCamelContext()
—References theCamelContext
to which thisComponent
belongs. ThesetCamelContext()
method is automatically called when you add the component to aCamelContext
.createEndpoint()
—The factory method that gets called to createEndpoint
instances for this component. Theuri
parameter is the endpoint URI, which contains the details required to create the endpoint.
47.2. Implementing the Component Interface
The DefaultComponent class
org.apache.camel.impl.DefaultComponent
class, which provides some standard functionality and default implementations for some of the methods. In particular, the DefaultComponent
class provides support for URI parsing and for creating a scheduled executor (which is used for the scheduled poll pattern).
URI parsing
createEndpoint(String uri)
method defined in the base Component
interface takes a complete, unparsed endpoint URI as its sole argument. The DefaultComponent
class, on the other hand, defines a three-argument version of the createEndpoint()
method with the following signature:
protected abstract Endpoint createEndpoint( String uri, String remaining, Map parameters ) throws Exception;
uri
is the original, unparsed URI; remaining
is the part of the URI that remains after stripping off the component prefix at the start and cutting off the query options at the end; and parameters
contains the parsed query options. It is this version of the createEndpoint()
method that you must override when inheriting from DefaultComponent
. This has the advantage that the endpoint URI is already parsed for you.
file
component shows how URI parsing works in practice:
file:///tmp/messages/foo?delete=true&moveNamePostfix=.old
createEndpoint()
:
Argument | Sample Value |
---|---|
uri | file:///tmp/messages/foo?delete=true&moveNamePostfix=.old |
remaining | /tmp/messages/foo |
parameters |
Two entries are set in
java.util.Map :
|
Parameter injection
DefaultComponent
class automatically injects the parameters for you.
delete
and moveNamePostfix
. All you must do is define the corresponding bean methods (getters and setters) in the endpoint class:
public class FileEndpoint extends ScheduledPollEndpoint { ... public boolean isDelete() { return delete; } public void setDelete(boolean delete) { this.delete = delete; } ... public String getMoveNamePostfix() { return moveNamePostfix; } public void setMoveNamePostfix(String moveNamePostfix) { this.moveNamePostfix = moveNamePostfix; } }
Disabling endpoint parameter injection
Endpoint
class, you can optimize the process of endpoint creation by disabling endpoint parameter injection. To disable parameter injection on endpoints, override the useIntrospectionOnEndpoint()
method and implement it to return false
, as follows:
protected boolean useIntrospectionOnEndpoint() { return false; }
useIntrospectionOnEndpoint()
method does not affect the parameter injection that might be performed on a Consumer
class. Parameter injection at that level is controlled by the Endpoint.configureProperties()
method (see Section 48.2, “Implementing the Endpoint Interface”).
Scheduled executor service
ExecutorServiceStrategy
object that is returned by the CamelContext.getExecutorServiceStrategy()
method. For details of the Apache Camel threading model, see Section 2.8, “Threading Model”.
DefaultComponent
class provided a getExecutorService()
method for creating thread pool instances. Since 2.3, however, the creation of thread pools is now managed centrally by the ExecutorServiceStrategy
object.
Validating the URI
validateURI()
method from the DefaultComponent
class, which has the following signature:
protected void validateURI(String uri,
String path,
Map parameters)
throws ResolveEndpointFailedException;
validateURI()
should throw the org.apache.camel.ResolveEndpointFailedException
exception.
Creating an endpoint
createEndpoint()
” outlines how to implement the DefaultComponent.createEndpoint()
method, which is responsible for creating endpoint instances on demand.
Example 47.2. Implementation of createEndpoint()
- 1
- The CustomComponent is the name of your custom component class, which is defined by extending the
DefaultComponent
class. - 2
- When extending
DefaultComponent
, you must implement thecreateEndpoint()
method with three arguments (see the section called “URI parsing”). - 3
- Create an instance of your custom endpoint type, CustomEndpoint, by calling its constructor. At a minimum, this constructor takes a copy of the original URI string,
uri
, and a reference to this component instance,this
.
Example
FileComponent
class.
Example 47.3. FileComponent Implementation
package org.apache.camel.component.file; import org.apache.camel.CamelContext; import org.apache.camel.Endpoint; import org.apache.camel.impl.DefaultComponent; import java.io.File; import java.util.Map; public class FileComponent extends DefaultComponent { public static final String HEADER_FILE_NAME = "org.apache.camel.file.name"; public FileComponent() { 1 } public FileComponent(CamelContext context) { 2 super(context); } protected Endpoint createEndpoint(String uri, String remaining, Map parameters) throws Exception { 3 File file = new File(remaining); FileEndpoint result = new FileEndpoint(file, uri, this); return result; } }
- 1
- Always define a no-argument constructor for the component class in order to facilitate automatic instantiation of the class.
- 2
- A constructor that takes the parent
CamelContext
instance as an argument is convenient when creating a component instance by programming. - 3
- The implementation of the
FileComponent.createEndpoint()
method follows the pattern described in Example 47.2, “Implementation ofcreateEndpoint()
”. The implementation creates aFileEndpoint
object.
SynchronizationRouteAware Interface
SynchronizationRouteAware
interface allows you to have callbacks before and after the exchange has been routed.
onBeforeRoute
: Invoked before the exchange has been routed by the given route. However, this callback may not get invoked, if you add theSynchronizationRouteAware
implementation to theUnitOfWork
, after starting the route.onAfterRoute
: Invoked after the exchange has been routed by the given route. However, if the exchange is being routed through multiple routes, it would generate call backs for each route.This invocation occurs before these callbacks:- The consumer of the route writes any response back to the caller (if in
InOut
mode) - The
UnitOfWork
is done by calling eitherSynchronization.onComplete(org.apache.camel.Exchange)
orSynchronization.onFailure(org.apache.camel.Exchange)
Chapter 48. Endpoint Interface
Abstract
Endpoint
interface, which is an essential step in the implementation of a Apache Camel component.
48.1. The Endpoint Interface
Overview
org.apache.camel.Endpoint
type encapsulates an endpoint URI, and it also serves as a factory for Consumer
, Producer
, and Exchange
objects. There are three different approaches to implementing an endpoint:
- Event-driven
- scheduled poll
- polling
Endpoint
inheritance hierarchy.
Figure 48.1. Endpoint Inheritance Hierarchy
The Endpoint interface
org.apache.camel.Endpoint
interface.
Example 48.1. Endpoint Interface
package org.apache.camel; public interface Endpoint { boolean isSingleton(); String getEndpointUri(); String getEndpointKey(); CamelContext getCamelContext(); void setCamelContext(CamelContext context); void configureProperties(Map options); boolean isLenientProperties(); Exchange createExchange(); Exchange createExchange(ExchangePattern pattern); Exchange createExchange(Exchange exchange); Producer createProducer() throws Exception; Consumer createConsumer(Processor processor) throws Exception; PollingConsumer createPollingConsumer() throws Exception; }
Endpoint methods
Endpoint
interface defines the following methods:
isSingleton()
—Returnstrue
, if you want to ensure that each URI maps to a single endpoint within a CamelContext. When this property istrue
, multiple references to the identical URI within your routes always refer to a single endpoint instance. When this property isfalse
, on the other hand, multiple references to the same URI within your routes refer to distinct endpoint instances. Each time you refer to the URI in a route, a new endpoint instance is created.getEndpointUri()
—Returns the endpoint URI of this endpoint.getEndpointKey()
—Used byorg.apache.camel.spi.LifecycleStrategy
when registering the endpoint.getCamelContext()
—return a reference to theCamelContext
instance to which this endpoint belongs.setCamelContext()
—Sets theCamelContext
instance to which this endpoint belongs.configureProperties()
—Stores a copy of the parameter map that is used to inject parameters when creating a newConsumer
instance.isLenientProperties()
—Returnstrue
to indicate that the URI is allowed to contain unknown parameters (that is, parameters that cannot be injected on theEndpoint
or theConsumer
class). Normally, this method should be implemented to returnfalse
.createExchange()
—An overloaded method with the following variants:Exchange createExchange()
—Creates a new exchange instance with a default exchange pattern setting.Exchange createExchange(ExchangePattern pattern)
—Creates a new exchange instance with the specified exchange pattern.Exchange createExchange(Exchange exchange)
—Converts the givenexchange
argument to the type of exchange needed for this endpoint. If the given exchange is not already of the correct type, this method copies it into a new instance of the correct type. A default implementation of this method is provided in theDefaultEndpoint
class.
createProducer()
—Factory method used to create newProducer
instances.createConsumer()
—Factory method to create new event-driven consumer instances. Theprocessor
argument is a reference to the first processor in the route.createPollingConsumer()
—Factory method to create new polling consumer instances.
Endpoint singletons
isSingleton()
to return true
.
48.2. Implementing the Endpoint Interface
Alternative ways of implementing an endpoint
Event-driven endpoint implementation
org.apache.camel.impl.DefaultEndpoint
, as shown in Example 48.2, “Implementing DefaultEndpoint”.
Example 48.2. Implementing DefaultEndpoint
import java.util.Map; import java.util.concurrent.BlockingQueue; import org.apache.camel.Component; import org.apache.camel.Consumer; import org.apache.camel.Exchange; import org.apache.camel.Processor; import org.apache.camel.Producer; import org.apache.camel.impl.DefaultEndpoint; import org.apache.camel.impl.DefaultExchange; public class CustomEndpoint extends DefaultEndpoint { 1 public CustomEndpoint(String endpointUri, Component component) { 2 super(endpointUri, component); // Do any other initialization... } public Producer createProducer() throws Exception { 3 return new CustomProducer(this); } public Consumer createConsumer(Processor processor) throws Exception { 4 return new CustomConsumer(this, processor); } public boolean isSingleton() { return true; } // Implement the following methods, only if you need to set exchange properties. // public Exchange createExchange() { 5 return this.createExchange(getExchangePattern()); } public Exchange createExchange(ExchangePattern pattern) { Exchange result = new DefaultExchange(getCamelContext(), pattern); // Set exchange properties ... return result; } }
- 1
- Implement an event-driven custom endpoint, CustomEndpoint, by extending the
DefaultEndpoint
class. - 2
- You must have at least one constructor that takes the endpoint URI,
endpointUri
, and the parent component reference,component
, as arguments. - 3
- Implement the
createProducer()
factory method to create producer endpoints. - 4
- Implement the
createConsumer()
factory method to create event-driven consumer instances.ImportantDo not override thecreatePollingConsumer()
method. - 5
- In general, it is not necessary to override the
createExchange()
methods. The implementations inherited fromDefaultEndpoint
create aDefaultExchange
object by default, which can be used in any Apache Camel component. If you need to initialize some exchange properties in theDefaultExchange
object, however, it is appropriate to override thecreateExchange()
methods here in order to add the exchange property settings.
DefaultEndpoint
class provides default implementations of the following methods, which you might find useful when writing your custom endpoint code:
getEndpointUri()
—Returns the endpoint URI.getCamelContext()
—Returns a reference to theCamelContext
.getComponent()
—Returns a reference to the parent component.createPollingConsumer()
—Creates a polling consumer. The created polling consumer's functionality is based on the event-driven consumer. If you override the event-driven consumer method,createConsumer()
, you get a polling consumer implementation for free.createExchange(Exchange e)
—Converts the given exchange object,e
, to the type required for this endpoint. This method creates a new endpoint using the overriddencreateExchange()
endpoints. This ensures that the method also works for custom exchange types.
Scheduled poll endpoint implementation
org.apache.camel.impl.ScheduledPollEndpoint
, as shown in Example 48.3, “ScheduledPollEndpoint Implementation”.
Example 48.3. ScheduledPollEndpoint Implementation
import org.apache.camel.Consumer; import org.apache.camel.Processor; import org.apache.camel.Producer; import org.apache.camel.ExchangePattern; import org.apache.camel.Message; import org.apache.camel.impl.ScheduledPollEndpoint; public class CustomEndpoint extends ScheduledPollEndpoint { 1 protected CustomEndpoint(String endpointUri, CustomComponent component) { 2 super(endpointUri, component); // Do any other initialization... } public Producer createProducer() throws Exception { 3 Producer result = new CustomProducer(this); return result; } public Consumer createConsumer(Processor processor) throws Exception { 4 Consumer result = new CustomConsumer(this, processor); configureConsumer(result); 5 return result; } public boolean isSingleton() { return true; } // Implement the following methods, only if you need to set exchange properties. // public Exchange createExchange() { 6 return this.createExchange(getExchangePattern()); } public Exchange createExchange(ExchangePattern pattern) { Exchange result = new DefaultExchange(getCamelContext(), pattern); // Set exchange properties ... return result; } }
- 1
- Implement a scheduled poll custom endpoint, CustomEndpoint, by extending the
ScheduledPollEndpoint
class. - 2
- You must to have at least one constructor that takes the endpoint URI,
endpointUri
, and the parent component reference,component
, as arguments. - 3
- Implement the
createProducer()
factory method to create a producer endpoint. - 4
- Implement the
createConsumer()
factory method to create a scheduled poll consumer instance.ImportantDo not override thecreatePollingConsumer()
method. - 5
- The
configureConsumer()
method, defined in theScheduledPollEndpoint
base class, is responsible for injecting consumer query options into the consumer. See the section called “Consumer parameter injection”. - 6
- In general, it is not necessary to override the
createExchange()
methods. The implementations inherited fromDefaultEndpoint
create aDefaultExchange
object by default, which can be used in any Apache Camel component. If you need to initialize some exchange properties in theDefaultExchange
object, however, it is appropriate to override thecreateExchange()
methods here in order to add the exchange property settings.
Polling endpoint implementation
org.apache.camel.impl.DefaultPollingEndpoint
, as shown in Example 48.4, “DefaultPollingEndpoint Implementation”.
Example 48.4. DefaultPollingEndpoint Implementation
import org.apache.camel.Consumer; import org.apache.camel.Processor; import org.apache.camel.Producer; import org.apache.camel.ExchangePattern; import org.apache.camel.Message; import org.apache.camel.impl.DefaultPollingEndpoint; public class CustomEndpoint extends DefaultPollingEndpoint { ... public PollingConsumer createPollingConsumer() throws Exception { PollingConsumer result = new CustomConsumer(this); configureConsumer(result); return result; } // Do NOT implement createConsumer(). It is already implemented in DefaultPollingEndpoint. ... }
createPollingConsumer()
method instead of the createConsumer()
method. The consumer instance returned from createPollingConsumer()
must inherit from the PollingConsumer
interface. For details of how to implement a polling consumer, see the section called “Polling consumer implementation”.
createPollingConsumer()
method, the steps for implementing a DefaultPollingEndpoint
are similar to the steps for implementing a ScheduledPollEndpoint
. See Example 48.3, “ScheduledPollEndpoint Implementation” for details.
Implementing the BrowsableEndpoint interface
org.apache.camel.spi.BrowsableEndpoint
interface, as shown in Example 48.5, “BrowsableEndpoint Interface”. It makes sense to implement this interface if the endpoint performs some sort of buffering of incoming events. For example, the Apache Camel SEDA endpoint implements the BrowsableEndpoint
interface—see Example 48.6, “SedaEndpoint Implementation”.
Example 48.5. BrowsableEndpoint Interface
package org.apache.camel.spi; import java.util.List; import org.apache.camel.Endpoint; import org.apache.camel.Exchange; public interface BrowsableEndpoint extends Endpoint { List<Exchange> getExchanges(); }
Example
SedaEndpoint
. The SEDA endpoint is an example of an event-driven endpoint. Incoming events are stored in a FIFO queue (an instance of java.util.concurrent.BlockingQueue
) and a SEDA consumer starts up a thread to read and process the events. The events themselves are represented by org.apache.camel.Exchange
objects.
Example 48.6. SedaEndpoint Implementation
package org.apache.camel.component.seda; import java.util.ArrayList; import java.util.List; import java.util.Map; import java.util.concurrent.BlockingQueue; import org.apache.camel.Component; import org.apache.camel.Consumer; import org.apache.camel.Exchange; import org.apache.camel.Processor; import org.apache.camel.Producer; import org.apache.camel.impl.DefaultEndpoint; import org.apache.camel.spi.BrowsableEndpoint; public class SedaEndpoint extends DefaultEndpoint implements BrowsableEndpoint { 1 private BlockingQueue<Exchange> queue; public SedaEndpoint(String endpointUri, Component component, BlockingQueue<Exchange> queue) { 2 super(endpointUri, component); this.queue = queue; } public SedaEndpoint(String uri, SedaComponent component, Map parameters) { 3 this(uri, component, component.createQueue(uri, parameters)); } public Producer createProducer() throws Exception { 4 return new CollectionProducer(this, getQueue()); } public Consumer createConsumer(Processor processor) throws Exception { 5 return new SedaConsumer(this, processor); } public BlockingQueue<Exchange> getQueue() { 6 return queue; } public boolean isSingleton() { 7 return true; } public List<Exchange> getExchanges() { 8 return new ArrayList<Exchange>(getQueue()); } }
- 1
- The
SedaEndpoint
class follows the pattern for implementing an event-driven endpoint by extending theDefaultEndpoint
class. TheSedaEndpoint
class also implements theBrowsableEndpoint
interface, which provides access to the list of exchange objects in the queue. - 2
- Following the usual pattern for an event-driven consumer,
SedaEndpoint
defines a constructor that takes an endpoint argument,endpointUri
, and a component reference argument,component
. - 3
- Another constructor is provided, which delegates queue creation to the parent component instance.
- 4
- The
createProducer()
factory method creates an instance ofCollectionProducer
, which is a producer implementation that adds events to the queue. - 5
- The
createConsumer()
factory method creates an instance ofSedaConsumer
, which is responsible for pulling events off the queue and processing them. - 6
- The
getQueue()
method returns a reference to the queue. - 7
- The
isSingleton()
method returnstrue
, indicating that a single endpoint instance should be created for each unique URI string. - 8
- The
getExchanges()
method implements the corresponding abstract method fromBrowsableEndpoint
.
Chapter 49. Consumer Interface
Abstract
Consumer
interface, which is an essential step in the implementation of a Apache Camel component.
49.1. The Consumer Interface
Overview
org.apache.camel.Consumer
type represents a source endpoint in a route. There are several different ways of implementing a consumer (see Section 46.1.3, “Consumer Patterns and Threading”), and this degree of flexibility is reflected in the inheritance hierarchy ( see Figure 49.1, “Consumer Inheritance Hierarchy”), which includes several different base classes for implementing a consumer.
Figure 49.1. Consumer Inheritance Hierarchy
Consumer parameter injection
custom
prefix:
custom:destination?consumer.myConsumerParam
consumer.*
. For the consumer.myConsumerParam
parameter, you need to define corresponding setter and getter methods on the Consumer
implementation class as follows:
public class CustomConsumer extends ScheduledPollConsumer { ... String getMyConsumerParam() { ... } void setMyConsumerParam(String s) { ... } ... }
configureConsumer()
method in the implementation of Endpoint.createConsumer()
. See the section called “Scheduled poll endpoint implementation”). Example 49.1, “FileEndpoint createConsumer() Implementation” shows an example of a createConsumer()
method implementation, taken from the FileEndpoint
class in the file component:
Example 49.1. FileEndpoint createConsumer() Implementation
... public class FileEndpoint extends ScheduledPollEndpoint { ... public Consumer createConsumer(Processor processor) throws Exception { Consumer result = new FileConsumer(this, processor); configureConsumer(result); return result; } ... }
- When the endpoint is created, the default implementation of
DefaultComponent.createEndpoint(String uri)
parses the URI to extract the consumer parameters, and stores them in the endpoint instance by callingScheduledPollEndpoint.configureProperties()
. - When
createConsumer()
is called, the method implementation callsconfigureConsumer()
to inject the consumer parameters (see Example 49.1, “FileEndpoint createConsumer() Implementation”). - The
configureConsumer()
method uses Java reflection to call the setter methods whose names match the relevant options after theconsumer.
prefix has been stripped off.
Scheduled poll parameters
Name | Default | Description |
---|---|---|
initialDelay | 1000 | Delay, in milliseconds, before the first poll. |
delay | 500 | Depends on the value of the useFixedDelay flag (time unit is milliseconds). |
useFixedDelay | false |
If
false , the delay parameter is interpreted as the polling period. Polls will occur at initialDelay , initialDelay+delay , initialDelay+2*delay , and so on.
If
true , the delay parameter is interpreted as the time elapsed between the previous execution and the next execution. Polls will occur at initialDelay , initialDelay+[ProcessingTime]+delay , and so on. Where ProcessingTime is the time taken to process an exchange object in the current thread.
|
Converting between event-driven and polling consumers
org.apache.camel.impl.EventDrivenPollingConsumer
—Converts an event-driven consumer into a polling consumer instance.org.apache.camel.impl.DefaultScheduledPollConsumer
—Converts a polling consumer into an event-driven consumer instance.
Endpoint
type. The Endpoint
interface defines the following two methods for creating a consumer instance:
package org.apache.camel; public interface Endpoint { ... Consumer createConsumer(Processor processor) throws Exception; PollingConsumer createPollingConsumer() throws Exception; }
createConsumer()
returns an event-driven consumer and createPollingConsumer()
returns a polling consumer. You would only implement one these methods. For example, if you are following the event-driven pattern for your consumer, you would implement the createConsumer()
method provide a method implementation for createPollingConsumer()
that simply raises an exception. With the help of the conversion classes, however, Apache Camel is able to provide a more useful default implementation.
DefaultEndpoint
and implementing the createConsumer()
method. The implementation of createPollingConsumer()
is inherited from DefaultEndpoint
, where it is defined as follows:
public PollingConsumer<E> createPollingConsumer() throws Exception { return new EventDrivenPollingConsumer<E>(this); }
EventDrivenPollingConsumer
constructor takes a reference to the event-driven consumer, this
, effectively wrapping it and converting it into a polling consumer. To implement the conversion, the EventDrivenPollingConsumer
instance buffers incoming events and makes them available on demand through the receive()
, the receive(long timeout)
, and the receiveNoWait()
methods.
DefaultPollingEndpoint
and implementing the createPollingConsumer()
method. In this case, the implementation of the createConsumer()
method is inherited from DefaultPollingEndpoint
, and the default implementation returns a DefaultScheduledPollConsumer
instance (which converts the polling consumer into an event-driven consumer).
ShutdownPrepared interface
org.apache.camel.spi.ShutdownPrepared
interface, which enables your custom consumer endpoint to receive shutdown notifications.
ShutdownPrepared
interface.
Example 49.2. ShutdownPrepared Interface
package org.apache.camel.spi; public interface ShutdownPrepared { void prepareShutdown(boolean forced); }
ShutdownPrepared
interface defines the following methods:
prepareShutdown
- Receives notifications to shut down the consumer endpoint in one or two phases, as follows:
- Graceful shutdown—where the
forced
argument has the valuefalse
. Attempt to clean up resources gracefully. For example, by stopping threads gracefully. - Forced shutdown—where the
forced
argument has the valuetrue
. This means that the shutdown has timed out, so you must clean up resources more aggressively. This is the last chance to clean up resources before the process exits.
ShutdownAware interface
org.apache.camel.spi.ShutdownAware
interface, which interacts with the graceful shutdown mechanism, enabling a consumer to ask for extra time to shut down. This is typically needed for components such as SEDA, which can have pending exchanges stored in an internal queue. Normally, you would want to process all of the exchanges in the queue before shutting down the SEDA consumer.
ShutdownAware
interface.
Example 49.3. ShutdownAware Interface
// Java package org.apache.camel.spi; import org.apache.camel.ShutdownRunningTask; public interface ShutdownAware extends ShutdownPrepared { boolean deferShutdown(ShutdownRunningTask shutdownRunningTask); int getPendingExchangesSize(); }
ShutdownAware
interface defines the following methods:
deferShutdown
- Return
true
from this method, if you want to delay shutdown of the consumer. TheshutdownRunningTask
argument is anenum
which can take either of the following values:ShutdownRunningTask.CompleteCurrentTaskOnly
—finish processing the exchanges that are currently being processed by the consumer's thread pool, but do not attempt to process any more exchanges than that.ShutdownRunningTask.CompleteAllTasks
—process all of the pending exchanges. For example, in the case of the SEDA component, the consumer would process all of the exchanges from its incoming queue.
getPendingExchangesSize
- Indicates how many exchanges remain to be processed by the consumer. A zero value indicates that processing is finished and the consumer can be shut down.
ShutdownAware
methods, see Example 49.7, “Custom Threading Implementation”.
49.2. Implementing the Consumer Interface
Alternative ways of implementing a consumer
Event-driven consumer implementation
JMXConsumer
class, which is taken from the Apache Camel JMX component implementation. The JMXConsumer
class is an example of an event-driven consumer, which is implemented by inheriting from the org.apache.camel.impl.DefaultConsumer
class. In the case of the JMXConsumer
example, events are represented by calls on the NotificationListener.handleNotification()
method, which is a standard way of receiving JMX events. In order to receive these JMX events, it is necessary to implement the NotificationListener
interface and override the handleNotification()
method, as shown in Example 49.4, “JMXConsumer Implementation”.
Example 49.4. JMXConsumer Implementation
package org.apache.camel.component.jmx; import javax.management.Notification; import javax.management.NotificationListener; import org.apache.camel.Processor; import org.apache.camel.impl.DefaultConsumer; public class JMXConsumer extends DefaultConsumer implements NotificationListener { 1 JMXEndpoint jmxEndpoint; public JMXConsumer(JMXEndpoint endpoint, Processor processor) { 2 super(endpoint, processor); this.jmxEndpoint = endpoint; } public void handleNotification(Notification notification, Object handback) { 3 try { getProcessor().process(jmxEndpoint.createExchange(notification)); 4 } catch (Throwable e) { handleException(e); 5 } } }
- 1
- The
JMXConsumer
pattern follows the usual pattern for event-driven consumers by extending theDefaultConsumer
class. Additionally, because this consumer is designed to receive events from JMX (which are represented by JMX notifications), it is necessary to implement theNotificationListener
interface. - 2
- You must implement at least one constructor that takes a reference to the parent endpoint,
endpoint
, and a reference to the next processor in the chain,processor
, as arguments. - 3
- The
handleNotification()
method (which is defined inNotificationListener
) is automatically invoked by JMX whenever a JMX notification arrives. The body of this method should contain the code that performs the consumer's event processing. Because thehandleNotification()
call originates from the JMX layer, the consumer's threading model is implicitly controlled by the JMX layer, not by theJMXConsumer
class.NoteThehandleNotification()
method is specific to the JMX example. When implementing your own event-driven consumer, you must identify an analogous event listener method to implement in your custom consumer. - 4
- This line of code combines two steps. First, the JMX notification object is converted into an exchange object, which is the generic representation of an event in Apache Camel. Then the newly created exchange object is passed to the next processor in the route (invoked synchronously).
- 5
- The
handleException()
method is implemented by theDefaultConsumer
base class. By default, it handles exceptions using theorg.apache.camel.impl.LoggingExceptionHandler
class.
Scheduled poll consumer implementation
java.util.concurrent.ScheduledExecutorService
. To receive the generated polling events, you must implement the ScheduledPollConsumer.poll()
method (see Section 46.1.3, “Consumer Patterns and Threading”).
ScheduledPollConsumer
class.
Example 49.5. ScheduledPollConsumer Implementation
import java.util.concurrent.ScheduledExecutorService; import org.apache.camel.Consumer; import org.apache.camel.Endpoint; import org.apache.camel.Exchange; import org.apache.camel.Message; import org.apache.camel.PollingConsumer; import org.apache.camel.Processor; import org.apache.camel.impl.ScheduledPollConsumer; public class CustomConsumer extends ScheduledPollConsumer { 1 private final CustomEndpoint endpoint; public CustomConsumer(CustomEndpoint endpoint, Processor processor) { 2 super(endpoint, processor); this.endpoint = endpoint; } protected void poll() throws Exception { 3 Exchange exchange = /* Receive exchange object ... */; // Example of a synchronous processor. getProcessor().process(exchange); 4 } @Override protected void doStart() throws Exception { 5 // Pre-Start: // Place code here to execute just before start of processing. super.doStart(); // Post-Start: // Place code here to execute just after start of processing. } @Override protected void doStop() throws Exception { 6 // Pre-Stop: // Place code here to execute just before processing stops. super.doStop(); // Post-Stop: // Place code here to execute just after processing stops. } }
- 1
- Implement a scheduled poll consumer class, CustomConsumer, by extending the
org.apache.camel.impl.ScheduledPollConsumer
class. - 2
- You must implement at least one constructor that takes a reference to the parent endpoint,
endpoint
, and a reference to the next processor in the chain,processor
, as arguments. - 3
- Override the
poll()
method to receive the scheduled polling events. This is where you should put the code that retrieves and processes incoming events (represented by exchange objects). - 4
- In this example, the event is processed synchronously. If you want to process events asynchronously, you should use a reference to an asynchronous processor instead, by calling
getAsyncProcessor()
. For details of how to process events asynchronously, see Section 46.1.4, “Asynchronous Processing”. - 5
- (Optional) If you want some lines of code to execute as the consumer is starting up, override the
doStart()
method as shown. - 6
- (Optional) If you want some lines of code to execute as the consumer is stopping, override the
doStop()
method as shown.
Polling consumer implementation
PollingConsumerSupport
class.
Example 49.6. PollingConsumerSupport Implementation
import org.apache.camel.Exchange; import org.apache.camel.RuntimeCamelException; import org.apache.camel.impl.PollingConsumerSupport; public class CustomConsumer extends PollingConsumerSupport { 1 private final CustomEndpoint endpoint; public CustomConsumer(CustomEndpoint endpoint) { 2 super(endpoint); this.endpoint = endpoint; } public Exchange receiveNoWait() { 3 Exchange exchange = /* Obtain an exchange object. */; // Further processing ... return exchange; } public Exchange receive() { 4 // Blocking poll ... } public Exchange receive(long timeout) { 5 // Poll with timeout ... } protected void doStart() throws Exception { 6 // Code to execute whilst starting up. } protected void doStop() throws Exception { // Code to execute whilst shutting down. } }
- 1
- Implement your polling consumer class, CustomConsumer, by extending the
org.apache.camel.impl.PollingConsumerSupport
class. - 2
- You must implement at least one constructor that takes a reference to the parent endpoint,
endpoint
, as an argument. A polling consumer does not need a reference to a processor instance. - 3
- The
receiveNoWait()
method should implement a non-blocking algorithm for retrieving an event (exchange object). If no event is available, it should returnnull
. - 4
- The
receive()
method should implement a blocking algorithm for retrieving an event. This method can block indefinitely, if events remain unavailable. - 5
- The
receive(long timeout)
method implements an algorithm that can block for as long as the specified timeout (typically specified in units of milliseconds). - 6
- If you want to insert code that executes while a consumer is starting up or shutting down, implement the
doStart()
method and thedoStop()
method, respectively.
Custom threading implementation
Consumer
interface directly and write the threading code yourself. When writing the threading code, however, it is important that you comply with the standard Apache Camel threading model, as described in Section 2.8, “Threading Model”.
camel-core
implements its own consumer threading, which is consistent with the Apache Camel threading model. Example 49.7, “Custom Threading Implementation” shows an outline of how the SedaConsumer
class implements its threading.
Example 49.7. Custom Threading Implementation
package org.apache.camel.component.seda; import java.util.ArrayList; import java.util.List; import java.util.concurrent.BlockingQueue; import java.util.concurrent.ExecutorService; import java.util.concurrent.TimeUnit; import org.apache.camel.Consumer; import org.apache.camel.Endpoint; import org.apache.camel.Exchange; import org.apache.camel.Processor; import org.apache.camel.ShutdownRunningTask; import org.apache.camel.impl.LoggingExceptionHandler; import org.apache.camel.impl.ServiceSupport; import org.apache.camel.util.ServiceHelper; ... import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * A Consumer for the SEDA component. * * @version $Revision: 922485 $ */ public class SedaConsumer extends ServiceSupport implements Consumer, Runnable, ShutdownAware { 1 private static final transient Log LOG = LogFactory.getLog(SedaConsumer.class); private SedaEndpoint endpoint; private Processor processor; private ExecutorService executor; ... public SedaConsumer(SedaEndpoint endpoint, Processor processor) { this.endpoint = endpoint; this.processor = processor; } ... public void run() { 2 BlockingQueue<Exchange> queue = endpoint.getQueue(); // Poll the queue and process exchanges ... } ... protected void doStart() throws Exception { 3 int poolSize = endpoint.getConcurrentConsumers(); executor = endpoint.getCamelContext().getExecutorServiceStrategy() .newFixedThreadPool(this, endpoint.getEndpointUri(), poolSize); 4 for (int i = 0; i < poolSize; i++) { 5 executor.execute(this); } endpoint.onStarted(this); } protected void doStop() throws Exception { 6 endpoint.onStopped(this); // must shutdown executor on stop to avoid overhead of having them running endpoint.getCamelContext().getExecutorServiceStrategy().shutdownNow(executor); 7 executor = null; if (multicast != null) { ServiceHelper.stopServices(multicast); } } ... //---------- // Implementation of ShutdownAware interface public boolean deferShutdown(ShutdownRunningTask shutdownRunningTask) { // deny stopping on shutdown as we want seda consumers to run in case some other queues // depend on this consumer to run, so it can complete its exchanges return true; } public int getPendingExchangesSize() { // number of pending messages on the queue return endpoint.getQueue().size(); } }
- 1
- The
SedaConsumer
class is implemented by extending theorg.apache.camel.impl.ServiceSupport
class and implementing theConsumer
,Runnable
, andShutdownAware
interfaces. - 2
- Implement the
Runnable.run()
method to define what the consumer does while it is running in a thread. In this case, the consumer runs in a loop, polling the queue for new exchanges and then processing the exchanges in the latter part of the queue. - 3
- The
doStart()
method is inherited fromServiceSupport
. You override this method in order to define what the consumer does when it starts up. - 4
- Instead of creating threads directly, you should create a thread pool using the
ExecutorServiceStrategy
object that is registered with theCamelContext
. This is important, because it enables Apache Camel to implement centralized management of threads and support such features as graceful shutdown.For details, see Section 2.8, “Threading Model”. - 5
- Kick off the threads by calling the
ExecutorService.execute()
methodpoolSize
times. - 6
- The
doStop()
method is inherited fromServiceSupport
. You override this method in order to define what the consumer does when it shuts down. - 7
- Shut down the thread pool, which is represented by the
executor
instance.
Chapter 50. Producer Interface
Abstract
Producer
interface, which is an essential step in the implementation of a Apache Camel component.
50.1. The Producer Interface
Overview
org.apache.camel.Producer
type represents a target endpoint in a route. The role of the producer is to send requests (In messages) to a specific physical endpoint and to receive the corresponding response (Out or Fault message). A Producer
object is essentially a special kind of Processor
that appears at the end of a processor chain (equivalent to a route). Figure 50.1, “Producer Inheritance Hierarchy” shows the inheritance hierarchy for producers.
Figure 50.1. Producer Inheritance Hierarchy
The Producer interface
org.apache.camel.Producer
interface.
Example 50.1. Producer Interface
package org.apache.camel; public interface Producer extends Processor, Service, IsSingleton { Endpoint<E> getEndpoint(); Exchange createExchange(); Exchange createExchange(ExchangePattern pattern); Exchange createExchange(E exchange); }
Producer methods
Producer
interface defines the following methods:
process()
(inherited from Processor)—The most important method. A producer is essentially a special type of processor that sends a request to an endpoint, instead of forwarding the exchange object to another processor. By overriding theprocess()
method, you define how the producer sends and receives messages to and from the relevant endpoint.getEndpoint()
—Returns a reference to the parent endpoint instance.createExchange()
—These overloaded methods are analogous to the corresponding methods defined in theEndpoint
interface. Normally, these methods delegate to the corresponding methods defined on the parentEndpoint
instance (this is what theDefaultEndpoint
class does by default). Occasionally, you might need to override these methods.
Asynchronous processing
process()
method returns without delay. See Section 46.1.4, “Asynchronous Processing”.
org.apache.camel.AsyncProcessor
interface. On its own, this is not enough to ensure that the asynchronous processing model will be used: it is also necessary for the preceding processor in the chain to call the asynchronous version of the process()
method. The definition of the AsyncProcessor
interface is shown in Example 50.2, “AsyncProcessor Interface”.
Example 50.2. AsyncProcessor Interface
package org.apache.camel; public interface AsyncProcessor extends Processor { boolean process(Exchange exchange, AsyncCallback callback); }
process()
method takes an extra argument, callback
, of org.apache.camel.AsyncCallback
type. The corresponding AsyncCallback
interface is defined as shown in Example 50.3, “AsyncCallback Interface”.
Example 50.3. AsyncCallback Interface
package org.apache.camel; public interface AsyncCallback { void done(boolean doneSynchronously); }
AsyncProcessor.process()
must provide an implementation of AsyncCallback
to receive the notification that processing has finished. The AsyncCallback.done()
method takes a boolean argument that indicates whether the processing was performed synchronously or not. Normally, the flag would be false
, to indicate asynchronous processing. In some cases, however, it can make sense for the producer not to process asynchronously (in spite of being asked to do so). For example, if the producer knows that the processing of the exchange will complete rapidly, it could optimise the processing by doing it synchronously. In this case, the doneSynchronously
flag should be set to true
.
ExchangeHelper class
org.apache.camel.util.ExchangeHelper
utility class. For full details of the ExchangeHelper
class, see Section 43.4, “The ExchangeHelper Class”.
50.2. Implementing the Producer Interface
Alternative ways of implementing a producer
How to implement a synchronous producer
Producer.process()
blocks until a reply is received.
Example 50.4. DefaultProducer Implementation
import org.apache.camel.Endpoint; import org.apache.camel.Exchange; import org.apache.camel.Producer; import org.apache.camel.impl.DefaultProducer; public class CustomProducer extends DefaultProducer { 1 public CustomProducer(Endpoint endpoint) { 2 super(endpoint); // Perform other initialization tasks... } public void process(Exchange exchange) throws Exception { 3 // Process exchange synchronously. // ... } }
- 1
- Implement a custom synchronous producer class, CustomProducer, by extending the
org.apache.camel.impl.DefaultProducer
class. - 2
- Implement a constructor that takes a reference to the parent endpoint.
- 3
- The
process()
method implementation represents the core of the producer code. The implementation of theprocess()
method is entirely dependent on the type of component that you are implementing. In outline, theprocess()
method is normally implemented as follows:- If the exchange contains an In message, and if this is consistent with the specified exchange pattern, then send the In message to the designated endpoint.
- If the exchange pattern anticipates the receipt of an Out message, then wait until the Out message has been received. This typically causes the
process()
method to block for a significant length of time. - When a reply is received, call
exchange.setOut()
to attach the reply to the exchange object. If the reply contains a fault message, set the fault flag on the Out message usingMessage.setFault(true)
.
How to implement an asynchronous producer
process()
method and an asynchronous process()
method (which takes an additional AsyncCallback
argument).
Example 50.5. CollectionProducer Implementation
import org.apache.camel.AsyncCallback; import org.apache.camel.AsyncProcessor; import org.apache.camel.Endpoint; import org.apache.camel.Exchange; import org.apache.camel.Producer; import org.apache.camel.impl.DefaultProducer; public class CustomProducer extends DefaultProducer implements AsyncProcessor { 1 public CustomProducer(Endpoint endpoint) { 2 super(endpoint); // ... } public void process(Exchange exchange) throws Exception { 3 // Process exchange synchronously. // ... } public boolean process(Exchange exchange, AsyncCallback callback) { 4 // Process exchange asynchronously. CustomProducerTask task = new CustomProducerTask(exchange, callback); // Process 'task' in a separate thread... // ... return false; 5 } } public class CustomProducerTask implements Runnable { 6 private Exchange exchange; private AsyncCallback callback; public CustomProducerTask(Exchange exchange, AsyncCallback callback) { this.exchange = exchange; this.callback = callback; } public void run() { 7 // Process exchange. // ... callback.done(false); } }
- 1
- Implement a custom asynchronous producer class, CustomProducer, by extending the
org.apache.camel.impl.DefaultProducer
class, and implementing theAsyncProcessor
interface. - 2
- Implement a constructor that takes a reference to the parent endpoint.
- 3
- Implement the synchronous
process()
method. - 4
- Implement the asynchronous
process()
method. You can implement the asynchronous method in several ways. The approach shown here is to create ajava.lang.Runnable
instance,task
, that represents the code that runs in a sub-thread. You then use the Java threading API to run the task in a sub-thread (for example, by creating a new thread or by allocating the task to an existing thread pool). - 5
- Normally, you return
false
from the asynchronousprocess()
method, to indicate that the exchange was processed asynchronously. - 6
- The CustomProducer
Task
class encapsulates the processing code that runs in a sub-thread. This class must store a copy of theExchange
object,exchange
, and theAsyncCallback
object,callback
, as private member variables. - 7
- The
run()
method contains the code that sends the In message to the producer endpoint and waits to receive the reply, if any. After receiving the reply (Out message or Fault message) and inserting it into the exchange object, you must callcallback.done()
to notify the caller that processing is complete.
Chapter 51. Exchange Interface
Abstract
Exchange
interface. Since the refactoring of the camel-core module performed in Apache Camel 2.0, there is no longer any necessity to define custom exchange types. The DefaultExchange
implementation can now be used in all cases.
51.1. The Exchange Interface
Overview
org.apache.camel.Exchange
type encapsulates the current message passing through a route, with additional metadata encoded as exchange properties.
DefaultExchange
, is always used.
Figure 51.1. Exchange Inheritance Hierarchy
The Exchange interface
org.apache.camel.Exchange
interface.
Example 51.1. Exchange Interface
package org.apache.camel; import java.util.Map; import org.apache.camel.spi.Synchronization; import org.apache.camel.spi.UnitOfWork; public interface Exchange { // Exchange property names (string constants) // (Not shown here) ... ExchangePattern getPattern(); void setPattern(ExchangePattern pattern); Object getProperty(String name); Object getProperty(String name, Object defaultValue); <T> T getProperty(String name, Class<T> type); <T> T getProperty(String name, Object defaultValue, Class<T> type); void setProperty(String name, Object value); Object removeProperty(String name); Map<String, Object> getProperties(); boolean hasProperties(); Message getIn(); <T> T getIn(Class<T> type); void setIn(Message in); Message getOut(); <T> T getOut(Class<T> type); void setOut(Message out); boolean hasOut(); Throwable getException(); <T> T getException(Class<T> type); void setException(Throwable e); boolean isFailed(); boolean isTransacted(); boolean isRollbackOnly(); CamelContext getContext(); Exchange copy(); Endpoint getFromEndpoint(); void setFromEndpoint(Endpoint fromEndpoint); String getFromRouteId(); void setFromRouteId(String fromRouteId); UnitOfWork getUnitOfWork(); void setUnitOfWork(UnitOfWork unitOfWork); String getExchangeId(); void setExchangeId(String id); void addOnCompletion(Synchronization onCompletion); void handoverCompletions(Exchange target); }
Exchange methods
Exchange
interface defines the following methods:
getPattern()
,setPattern()
—The exchange pattern can be one of the values enumerated inorg.apache.camel.ExchangePattern
. The following exchange pattern values are supported:InOnly
RobustInOnly
InOut
InOptionalOut
OutOnly
RobustOutOnly
OutIn
OutOptionalIn
setProperty()
,getProperty()
,getProperties()
,removeProperty()
,hasProperties()
—Use the property setter and getter methods to associate named properties with the exchange instance. The properties consist of miscellaneous metadata that you might need for your component implementation.setIn()
,getIn()
—Setter and getter methods for the In message.ThegetIn()
implementation provided by theDefaultExchange
class implements lazy creation semantics: if the In message is null whengetIn()
is called, theDefaultExchange
class creates a default In message.setOut()
,getOut()
,hasOut()
—Setter and getter methods for the Out message.ThegetOut()
method implicitly supports lazy creation of an Out message. That is, if the current Out message isnull
, a new message instance is automatically created.setException()
,getException()
—Getter and setter methods for an exception object (ofThrowable
type).isFailed()
—Returnstrue
, if the exchange failed either due to an exception or due to a fault.isTransacted()
—Returnstrue
, if the exchange is transacted.isRollback()
—Returnstrue
, if the exchange is marked for rollback.getContext()
—Returns a reference to the associatedCamelContext
instance.copy()
—Creates a new, identical (apart from the exchange ID) copy of the current custom exchange object. The body and headers of the In message, the Out message (if any), and the Fault message (if any) are also copied by this operation.setFromEndpoint()
,getFromEndpoint()
—Getter and setter methods for the consumer endpoint that orginated this message (which is typically the endpoint appearing in thefrom()
DSL command at the start of a route).setFromRouteId()
,getFromRouteId()
—Getters and setters for the route ID that originated this exchange. ThegetFromRouteId()
method should only be called internally.setUnitOfWork()
,getUnitOfWork()
—Getter and setter methods for theorg.apache.camel.spi.UnitOfWork
bean property. This property is only required for exchanges that can participate in a transaction.setExchangeId()
,getExchangeId()
—Getter and setter methods for the exchange ID. Whether or not a custom component uses and exchange ID is an implementation detail.addOnCompletion()
—Adds anorg.apache.camel.spi.Synchronization
callback object, which gets called when processing of the exchange has completed.handoverCompletions()
—Hands over all of the OnCompletion callback objects to the specified exchange object.
Chapter 52. Message Interface
Abstract
Message
interface, which is an optional step in the implementation of a Apache Camel component.
52.1. The Message Interface
Overview
org.apache.camel.Message
type can represent any kind of message (In or Out). Figure 52.1, “Message Inheritance Hierarchy” shows the inheritance hierarchy for the message type. You do not always need to implement a custom message type for a component. In many cases, the default implementation, DefaultMessage
, is adequate.
Figure 52.1. Message Inheritance Hierarchy
The Message interface
org.apache.camel.Message
interface.
Example 52.1. Message Interface
package org.apache.camel; import java.util.Map; import java.util.Set; import javax.activation.DataHandler; public interface Message { String getMessageId(); void setMessageId(String messageId); Exchange getExchange(); boolean isFault(); void setFault(boolean fault); Object getHeader(String name); Object getHeader(String name, Object defaultValue); <T> T getHeader(String name, Class<T> type); <T> T getHeader(String name, Object defaultValue, Class<T> type); Map<String, Object> getHeaders(); void setHeader(String name, Object value); void setHeaders(Map<String, Object> headers); Object removeHeader(String name); boolean removeHeaders(String pattern); boolean hasHeaders(); Object getBody(); Object getMandatoryBody() throws InvalidPayloadException; <T> T getBody(Class<T> type); <T> T getMandatoryBody(Class<T> type) throws InvalidPayloadException; void setBody(Object body); <T> void setBody(Object body, Class<T> type); DataHandler getAttachment(String id); Map<String, DataHandler> getAttachments(); Set<String> getAttachmentNames(); void removeAttachment(String id); void addAttachment(String id, DataHandler content); void setAttachments(Map<String, DataHandler> attachments); boolean hasAttachments(); Message copy(); void copyFrom(Message message); String createExchangeId(); }
Message methods
Message
interface defines the following methods:
setMessageId()
,getMessageId()
—Getter and setter methods for the message ID. Whether or not you need to use a message ID in your custom component is an implementation detail.getExchange()
—Returns a reference to the parent exchange object.isFault()
,setFault()
—Getter and setter methods for the fault flag, which indicates whether or not this message is a fault message.getHeader()
,getHeaders()
,setHeader()
,setHeaders()
,removeHeader()
,hasHeaders()
—Getter and setter methods for the message headers. In general, these message headers can be used either to store actual header data, or to store miscellaneous metadata.getBody()
,getMandatoryBody()
,setBody()
—Getter and setter methods for the message body. The getMandatoryBody() accessor guarantees that the returned body is non-null, otherwise theInvalidPayloadException
exception is thrown.getAttachment()
,getAttachments()
,getAttachmentNames()
,removeAttachment()
,addAttachment()
,setAttachments()
,hasAttachments()
—Methods to get, set, add, and remove attachments.copy()
—Creates a new, identical (including the message ID) copy of the current custom message object.copyFrom()
—Copies the complete contents (including the message ID) of the specified generic message object,message
, into the current message instance. Because this method must be able to copy from any message type, it copies the generic message properties, but not the custom properties.createExchangeId()
—Returns the unique ID for this exchange, if the message implementation is capable of providing an ID; otherwise, returnnull
.
52.2. Implementing the Message Interface
How to implement a custom message
DefaultMessage
class.
Example 52.2. Custom Message Implementation
import org.apache.camel.Exchange; import org.apache.camel.impl.DefaultMessage; public class CustomMessage extends DefaultMessage { 1 public CustomMessage() { 2 // Create message with default properties... } @Override public String toString() { 3 // Return a stringified message... } @Override public CustomMessage newInstance() { 4 return new CustomMessage( ... ); } @Override protected Object createBody() { 5 // Return message body (lazy creation). } @Override protected void populateInitialHeaders(Map<String, Object> map) { 6 // Initialize headers from underlying message (lazy creation). } @Override protected void populateInitialAttachments(Map<String, DataHandler> map) { 7 // Initialize attachments from underlying message (lazy creation). } }
- 1
- Implements a custom message class, CustomMessage, by extending the
org.apache.camel.impl.DefaultMessage
class. - 2
- Typically, you need a default constructor that creates a message with default properties.
- 3
- Override the
toString()
method to customize message stringification. - 4
- The
newInstance()
method is called from inside theMessageSupport.copy()
method. Customization of thenewInstance()
method should focus on copying all of the custom properties of the current message instance into the new message instance. TheMessageSupport.copy()
method copies the generic message properties by callingcopyFrom()
. - 5
- The
createBody()
method works in conjunction with theMessageSupport.getBody()
method to implement lazy access to the message body. By default, the message body isnull
. It is only when the application code tries to access the body (by callinggetBody()
), that the body should be created. TheMessageSupport.getBody()
automatically callscreateBody()
, when the message body is accessed for the first time. - 6
- The
populateInitialHeaders()
method works in conjunction with the header getter and setter methods to implement lazy access to the message headers. This method parses the message to extract any message headers and inserts them into the hash map,map
. ThepopulateInitialHeaders()
method is automatically called when a user attempts to access a header (or headers) for the first time (by callinggetHeader()
,getHeaders()
,setHeader()
, orsetHeaders()
). - 7
- The
populateInitialAttachments()
method works in conjunction with the attachment getter and setter methods to implement lazy access to the attachments. This method extracts the message attachments and inserts them into the hash map,map
. ThepopulateInitialAttachments()
method is automatically called when a user attempts to access an attachment (or attachments) for the first time by callinggetAttachment()
,getAttachments()
,getAttachmentNames()
, oraddAttachment()
.
Part V. The API Component Framework
Abstract
Chapter 53. Introduction to the API Component Framework
Abstract
53.1. What is the API Component Framework?
Motivation
Turning APIs into components
Generic URI format
scheme://endpoint-prefix/endpoint?Option1=Value1&...&OptionN=ValueN
scheme
is the default URI scheme defined by the component; endpoint-prefix
is a short API name, which maps to one of the classes or interfaces from the wrapped Java API; endpoint
maps to a method name; and the URI options map to method argument names.
URI format for a single API class
endpoint-prefix
part of the URI becomes redundant, and you can specify the URI in the following, shorter format:
scheme://endpoint?Option1=Value1&...&OptionN=ValueN
apiName
element blank in the configuration of the API component Maven plug-in.
Reflection and metadata
Javadoc
maven-javadoc-plugin
) and, in many cases, is already provided in a third-party library.
Method signature files
What does the framework consist of?
- A Maven archetype
- The
camel-archetype-api-component
Maven archetype is used to generate skeleton code for the component implementation. - A Maven plug-in
- The
camel-api-component-maven-plugin
Maven plug-in is responsible for generating the code that implements the mapping between the Java API and the endpoint URI syntax. - Specialized base classes
- To support the programming model of the API component framework, the Apache Camel core provides a specialized API in the
org.apache.camel.util.component
package. Amongst other things, this API provides specialized base classes for the component, endpoint, consumer, and producer classes.
53.2. How to use the Framework
Overview
Figure 53.1. Using the API Component Framework
Java API
- Implement the Java API yourself (though this typically would involve a lot of work and is generally not the preferred approach).
- Use a third-party Java API. For example, the Apache Camel Box component is based on the third-party Box Java SDK library.
- Generate the Java API from a language-neutral interface. For example, the Apache Camel LinkedIn component obtains its Java API by converting a WADL description of its REST services to Java (using the Apache CXF
wadl2java
tool).
Javadoc metadata
maven-javadoc-plugin
Maven plug-in.
java.util.List<String>
is supported, but java.util.List<java.util.List<String>>
is not. The workaround is to specify the nested generic type as java.util.List<java.util.List>
in a signature file.
Signature file metadata
- You must create one signature file for each proxy class (Java API class).
- The method signatures must not include a
raises
clause. All exceptions raised at runtime are wrapped in aRuntimeCamelException
and returned from the endpoint. - Class names that specify the type of an argument must be fully-qualified class names (except for the
java.lang.*
types). There is no mechanism for importing package names. - Currently, there is a limitation in the signature parser, such that generic nesting is not supported. For example,
java.util.List<String>
is supported, whereasjava.util.List<java.util.List<String>>
is not. The workaround is to specify the nested generic type asjava.util.List<java.util.List>
.
public String sayHi(); public String greetMe(String name); public String greetUs(String name1, String name2);
Generate starting code with the Maven archetype
camel-archetype-api-component
Maven archetype. For details of how to run the archetype, see Section 54.1, “Generate Code with the Maven Archetype”.
ProjectName
directory:
ProjectName-api
- This project contains the Java API, which forms the basis of the API component. When you build this project, it packages up the Java API in a Maven bundle and generates the requisite Javadoc as well. If the Java API and Javadoc are already provided by a third-party, however, you do not need this sub-project.
ProjectName-component
- This project contains the skeleton code for the API component.
Edit component classes
ProjectName-component
to develop your own component implementation. The following generated classes make up the core of the skeleton implementation:
ComponentNameComponent ComponentNameEndpoint ComponentNameConsumer ComponentNameProducer ComponentNameConfiguration
Customize POM files
camel-api-component-maven-plugin
Maven plug-in.
Configure the camel-api-component-maven-plugin
camel-api-component-maven-plugin
Maven plug-in. This plug-in is responsible for generating the mapping between API methods and endpoint URIs, and by editing the plug-in configuration, you can customize the mapping.
camel-api-component-maven-plugin
plug-in configuration shows a minimal configuration for an API class called ExampleJavadocHello
:
<configuration> <apis> <api> <apiName>hello-javadoc</apiName> <proxyClass>org.jboss.fuse.example.api.ExampleJavadocHello</proxyClass> <fromJavadoc/> </api> </apis> </configuration>
hello-javadoc
API name is mapped to the ExampleJavadocHello
class, which means you can invoke methods from this class using URIs of the form, scheme://hello-javadoc/endpoint
. The presence of the fromJavadoc
element indicates that the ExampleJavadocHello
class gets its metadata from Javadoc.
OSGi bundle configuration
ProjectName-component/pom.xml
, is configured to package the component as an OSGi bundle. The component POM includes a sample configuration of the maven-bundle-plugin
. You should customize the configuration of the maven-bundle-plugin
plug-in, to ensure that Maven generates a properly configured OSGi bundle for your component.
Build the component
camel-api-component-maven-plugin
plug-in automatically generates the API mapping classes (which define the mapping between the Java API and the endpoint URI syntax), placing them into the target/generated-classes
project subdirectory. When you are dealing with a large and complex Java API, this generated code actually constitutes the bulk of the component source code.
Chapter 54. Getting Started with the Framework
Abstract
camel-archetype-api-component
Maven archetype.
54.1. Generate Code with the Maven Archetype
Maven archetypes
The API component Maven archetype
camel-archetype-api-component
, that can generate starting point code for your own API component implementation. This is the recommended approach to start creating your own API component.
Prerequisites
camel-archetype-api-component
archetype are that Apache Maven is installed and the Maven settings.xml
file is configured to use the standard JBoss Fuse repositories. For more details, see appendix "Red Hat JBoss Fuse Maven Repositories" in "Installation Guide".
Invoke the Maven archetype
Example
component, which uses the example
URI scheme, invoke the camel-archetype-api-component
archetype to generate a new Maven project, as follows:
mvn archetype:generate \ -DarchetypeGroupId=org.apache.camel.archetypes \ -DarchetypeArtifactId=camel-archetype-api-component \ -DarchetypeVersion=2.15.1.redhat-620133 \ -DgroupId=org.jboss.fuse.example \ -DartifactId=camel-api-example \ -Dname=Example \ -Dscheme=example \ -Dversion=1.0-SNAPSHOT \ -DinteractiveMode=false
\
, at the end of each line represents line continuation, which works only on Linux and UNIX platforms. On Windows platforms, remove the backslash and put the arguments all on a single line.
Options
-DName=Value
. Most of the options should be set as shown in the preceding mvn archetype:generate
command, but a few of the options can be modified, to customize the generated project. The following table shows the options that you can use to customize the generated API component project:
Name | Description |
---|---|
groupId | (Generic Maven option) Specifies the group ID of the generated Maven project. By default, this value also defines the Java package name for the generated classes. Hence, it is a good idea to choose this value to match the Java package name that you want. |
artifactId | (Generic Maven option) Specifies the artifact ID of the generated Maven project. |
name | The name of the API component. This value is used for generating class names in the generated code (hence, it is recommended that the name should start with a capital letter). |
scheme | The default scheme to use in URIs for this component. You should make sure that this scheme does not conflict with the scheme of any existing Camel components. |
archetypeVersion | (Generic Maven option) Ideally, this should be the Apache Camel version used by the container where you plan to deploy the component. If necessary, however, you can also modify the versions of Maven dependencies after you have generated the project. |
Structure of the generated project
camel-api-example
, which contains the new Maven project. If you look inside the camel-api-example
directory, you will see that it has the following general structure:
camel-api-example/ pom.xml camel-api-example-api/ camel-api-example-component/
pom.xml
, which is configured to build two sub-projects, as follows:
- camel-api-example-api
- The API sub-project (named as
ArtifactId-api
) holds the Java API which you are about to turn into a component. If you are basing the API component on a Java API that you wrote yourself, you can put the Java API code directly into this project.The API sub-project can be used for one or more of the following purposes:- To package up the Java API code (if it is not already available as a Maven package).
- To generate Javadoc for the Java API (providing the needed metadata for the API component framework).
- To generate the Java API code from an API description (for example, from a WADL description of a REST API).
In some cases, however, you might not need to perform any of these tasks. For example, if the API component is based on a third-party API, which already provides the Java API and Javadoc in a Maven package. In such cases, you can delete the API sub-project. - camel-api-example-component
- The component sub-project (named as
ArtifactId-component
) holds the implementation of the new API component. This includes the component implementation classes and the configuration of thecamel-api-component-maven
plug-in (which generates the API mapping classes from the Java API).
54.2. Generated API Sub-Project
Overview
camel-api-example/camel-api-example-api
project directory. In this section, we take a closer look at the generated example code and describe how it works.
Sample Java API
ExampleJavadocHello
and ExampleFileHello
.
ExampleJavadocHello class
ExampleJavadocHello
class from the sample Java API. As the name of the class suggests, this particular class is used to show how you can supply mapping metadata from Javadoc.
Example 54.1. ExampleJavadocHello class
// Java package org.jboss.fuse.example.api; /** * Sample API used by Example Component whose method signatures are read from Javadoc. */ public class ExampleJavadocHello { public String sayHi() { return "Hello!"; } public String greetMe(String name) { return "Hello " + name; } public String greetUs(String name1, String name2) { return "Hello " + name1 + ", " + name2; } }
ExampleFileHello class
ExampleFileHello
class from the sample Java API. As the name of the class suggests, this particular class is used to show how you can supply mapping metadata from a signature file.
Example 54.2. ExampleFileHello class
// Java package org.jboss.fuse.example.api; /** * Sample API used by Example Component whose method signatures are read from File. */ public class ExampleFileHello { public String sayHi() { return "Hello!"; } public String greetMe(String name) { return "Hello " + name; } public String greetUs(String name1, String name2) { return "Hello " + name1 + ", " + name2; } }
Generating the Javadoc metadata for ExampleJavadocHello
ExampleJavadocHello
is provided as Javadoc, it is necessary to generate Javadoc for the sample Java API and install it into the camel-api-example-api
Maven artifact. The API POM file, camel-api-example-api/pom.xml
, configures the maven-javadoc-plugin
to perform this step automatically during the Maven build.
54.3. Generated Component Sub-Project
Overview
camel-api-example/camel-api-example-component
project directory. In this section, we take a closer look at the generated example code and describe how it works.
Providing the Java API in the component POM
camel-api-example-component/pom.xml
, as follows:
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> ... <dependencies> ... <dependency> <groupId>org.jboss.fuse.example</groupId> <artifactId>camel-api-example-api</artifactId> <version>1.0-SNAPSHOT</version> </dependency> ... </dependencies> ... </project>
Providing the Javadoc metadata in the component POM
- The Maven coordinates for the Javadoc are almost the same as for the Java API, except that you must also specify a
classifier
element, as follows:<classifier>javadoc</classifier>
- You must declare the Javadoc to have
provided
scope, as follows:<scope>provided</scope>
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> ... <dependencies> ... <!-- Component API javadoc in provided scope to read API signatures --> <dependency> <groupId>org.jboss.fuse.example</groupId> <artifactId>camel-api-example-api</artifactId> <version>1.0-SNAPSHOT</version> <classifier>javadoc</classifier> <scope>provided</scope> </dependency> ... </dependencies> ... </project>
Defining the file metadata for Example File Hello
ExampleFileHello
is provided in a signature file. In general, this file must be created manually, but it has quite a simple format, which consists of a list of method signatures (one on each line). The example code provides the signature file, file-sig-api.txt
, in the directory, camel-api-example-component/signatures
, which has the following contents:
public String sayHi(); public String greetMe(String name); public String greetUs(String name1, String name2);
Configuring the API mapping
camel-api-component-maven-plugin
Maven plug-in, which is configured in the component POM. The following extract from the component POM shows how the camel-api-component-maven-plugin
plug-in is configured:
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> ... <build> <defaultGoal>install</defaultGoal> <plugins> ... <!-- generate Component source and test source --> <plugin> <groupId>org.apache.camel</groupId> <artifactId>camel-api-component-maven-plugin</artifactId> <executions> <execution> <id>generate-test-component-classes</id> <goals> <goal>fromApis</goal> </goals> <configuration> <apis> <api> <apiName>hello-file</apiName> <proxyClass>org.jboss.fuse.example.api.ExampleFileHello</proxyClass> <fromSignatureFile>signatures/file-sig-api.txt</fromSignatureFile> </api> <api> <apiName>hello-javadoc</apiName> <proxyClass>org.jboss.fuse.example.api.ExampleJavadocHello</proxyClass> <fromJavadoc/> </api> </apis> </configuration> </execution> </executions> </plugin> ... </plugins> ... </build> ... </project>
configuration
element, which contains a single apis
child element to configure the classes of the Java API. Each API class is configured by an api
element, as follows:
apiName
- The API name is a short name for the API class and is used as the
endpoint-prefix
part of an endpoint URI.NoteIf the API consists of just a single Java class, you can leave theapiName
element empty, so that theendpoint-prefix
becomes redundant, and you can then specify the endpoint URI using the format shown in the section called “URI format for a single API class”. proxyClass
- The proxy class element specifies the fully-qualified name of the API class.
fromJavadoc
- If the API class is accompanied by Javadoc metadata, you must indicate this by including the
fromJavadoc
element and the Javadoc itself must also be specified in the Maven file, as aprovided
dependency (see the section called “Providing the Javadoc metadata in the component POM”). fromSignatureFile
- If the API class is accompanied by signature file metadata, you must indicate this by including the
fromSignatureFile
element, where the content of this element specifies the location of the signature file.NoteThe signature files do not get included in the final package built by Maven, because these files are needed only at build time, not at run time.
Generated component implementation
camel-api-example-component/src/main/java
directory:
ExampleComponent
- Represents the component itself. This class acts as a factory for endpoint instances (for example, instances of
ExampleEndpoint
). ExampleEndpoint
- Represents an endpoint URI. This class acts as a factory for consumer endpoints (for example,
ExampleConsumer
) and as a factory for producer endpoints (for example,ExampleProducer
). ExampleConsumer
- Represents a concrete instance of a consumer endpoint, which is capable of consuming messages from the location specified in the endpoint URI.
ExampleProducer
- Represents a concrete instance of a producer endpoint, which is capable of sending messages to the location specified in the endpoint URI.
ExampleConfiguration
- Can be used to define endpoint URI options. The URI options defined by this configuration class are not tied to any specific API class. That is, you can combine these URI options with any of the API classes or methods. This can be useful, for example, if you need to declare username and password credentials in order to connect to the remote service. The primary purpose of the
ExampleConfiguration
class is to provide values for parameters required to instantiate API classes, or classes that implement API interfaces. For example, these could be constructor parameters, or parameter values for a factory method or class.To implement a URI option,option
, in this class, all that you need to do is implement the pair of accessor methods,getOption
andsetOption
. The component framework automatically parses the endpoint URI and injects the option values at run time.
ExampleComponent class
ExampleComponent
class is defined as follows:
// Java package org.jboss.fuse.example; import org.apache.camel.CamelContext; import org.apache.camel.Endpoint; import org.apache.camel.spi.UriEndpoint; import org.apache.camel.util.component.AbstractApiComponent; import org.jboss.fuse.example.internal.ExampleApiCollection; import org.jboss.fuse.example.internal.ExampleApiName; /** * Represents the component that manages {@link ExampleEndpoint}. */ @UriEndpoint(scheme = "example", consumerClass = ExampleConsumer.class, consumerPrefix = "consumer") public class ExampleComponent extends AbstractApiComponent<ExampleApiName, ExampleConfiguration, ExampleApiCollection> { public ExampleComponent() { super(ExampleEndpoint.class, ExampleApiName.class, ExampleApiCollection.getCollection()); } public ExampleComponent(CamelContext context) { super(context, ExampleEndpoint.class, ExampleApiName.class, ExampleApiCollection.getCollection()); } @Override protected ExampleApiName getApiName(String apiNameStr) throws IllegalArgumentException { return ExampleApiName.fromValue(apiNameStr); } @Override protected Endpoint createEndpoint(String uri, String methodName, ExampleApiName apiName, ExampleConfiguration endpointConfiguration) { return new ExampleEndpoint(uri, this, apiName, methodName, endpointConfiguration); } }
createEndpoint
, which creates new endpoint instances. Typically, you do not need to change any of the default code in the component class. If there are any other objects with the same life cycle as this component, however, you might want to make those objects available from the component class (for example, by adding a methods to create those objects or by injecting those objects into the component).
ExampleEndpoint class
ExampleEndpoint
class is defined as follows:
// Java package org.jboss.fuse.example; import java.util.Map; import org.apache.camel.Consumer; import org.apache.camel.Processor; import org.apache.camel.Producer; import org.apache.camel.spi.UriEndpoint; import org.apache.camel.util.component.AbstractApiEndpoint; import org.apache.camel.util.component.ApiMethod; import org.apache.camel.util.component.ApiMethodPropertiesHelper; import org.jboss.fuse.example.api.ExampleFileHello; import org.jboss.fuse.example.api.ExampleJavadocHello; import org.jboss.fuse.example.internal.ExampleApiCollection; import org.jboss.fuse.example.internal.ExampleApiName; import org.jboss.fuse.example.internal.ExampleConstants; import org.jboss.fuse.example.internal.ExamplePropertiesHelper; /** * Represents a Example endpoint. */ @UriEndpoint(scheme = "example", consumerClass = ExampleConsumer.class, consumerPrefix = "consumer") public class ExampleEndpoint extends AbstractApiEndpoint<ExampleApiName, ExampleConfiguration> { // TODO create and manage API proxy private Object apiProxy; public ExampleEndpoint(String uri, ExampleComponent component, ExampleApiName apiName, String methodName, ExampleConfiguration endpointConfiguration) { super(uri, component, apiName, methodName, ExampleApiCollection.getCollection().getHelper(apiName), endpointConfiguration); } public Producer createProducer() throws Exception { return new ExampleProducer(this); } public Consumer createConsumer(Processor processor) throws Exception { // make sure inBody is not set for consumers if (inBody != null) { throw new IllegalArgumentException("Option inBody is not supported for consumer endpoint"); } final ExampleConsumer consumer = new ExampleConsumer(this, processor); // also set consumer.* properties configureConsumer(consumer); return consumer; } @Override protected ApiMethodPropertiesHelper<ExampleConfiguration> getPropertiesHelper() { return ExamplePropertiesHelper.getHelper(); } protected String getThreadProfileName() { return ExampleConstants.THREAD_PROFILE_NAME; } @Override protected void afterConfigureProperties() { // TODO create API proxy, set connection properties, etc. switch (apiName) { case HELLO_FILE: apiProxy = new ExampleFileHello(); break; case HELLO_JAVADOC: apiProxy = new ExampleJavadocHello(); break; default: throw new IllegalArgumentException("Invalid API name " + apiName); } } @Override public Object getApiProxy(ApiMethod method, Map<String, Object> args) { return apiProxy; } }
endpoint-prefix
appearing in the URI (recall that a URI has the general form, scheme://endpoint-prefix/endpoint
).
ExampleConsumer class
ExampleConsumer
class is defined as follows:
// Java package org.jboss.fuse.example; import org.apache.camel.Processor; import org.apache.camel.util.component.AbstractApiConsumer; import org.jboss.fuse.example.internal.ExampleApiName; /** * The Example consumer. */ public class ExampleConsumer extends AbstractApiConsumer<ExampleApiName, ExampleConfiguration> { public ExampleConsumer(ExampleEndpoint endpoint, Processor processor) { super(endpoint, processor); } }
ExampleProducer class
ExampleProducer
class is defined as follows:
// Java package org.jboss.fuse.example; import org.apache.camel.util.component.AbstractApiProducer; import org.jboss.fuse.example.internal.ExampleApiName; import org.jboss.fuse.example.internal.ExamplePropertiesHelper; /** * The Example producer. */ public class ExampleProducer extends AbstractApiProducer<ExampleApiName, ExampleConfiguration> { public ExampleProducer(ExampleEndpoint endpoint) { super(endpoint, ExamplePropertiesHelper.getHelper()); } }
ExampleConfiguration class
ExampleConfiguration
class is defined as follows:
// Java package org.jboss.fuse.example; import org.apache.camel.spi.UriParams; /** * Component configuration for Example component. */ @UriParams public class ExampleConfiguration { // TODO add component configuration properties }
option
, to this class, define a field of the appropriate type, and implement a corresponding pair of accessor methods, getOption
and setOption
. The component framework automatically parses the endpoint URI and injects the option values at run time.
URI format
scheme://endpoint-prefix/endpoint?Option1=Value1&...&OptionN=ValueN
ExampleJavadocHello.greetMe("Jane Doe")
, the URI would be constructed, as follows:
- [scheme]
- The API component scheme, as specified when you generated the code with the Maven archetype. In this case, the scheme is
example
. - [endpoint-prefix]
- The API name, which maps to the API class defined by the
camel-api-component-maven-plugin
Maven plug-in configuration. For theExampleJavadocHello
class, the relevant configuration is:<configuration> <apis> <api> <apiName>hello-javadoc</apiName> <proxyClass>org.jboss.fuse.example.api.ExampleJavadocHello</proxyClass> <fromJavadoc/> </api> ... </apis> </configuration>
Which shows that the requiredendpoint-prefix
ishello-javadoc
. - [endpoint]
- The
endpoint
maps to the method name, which isgreetMe
. - [Option1=Value1]
- The URI options specify method parameters. The
greetMe(String name)
method takes the single parameter,name
, which can be specified asname=Jane%20Doe
. If you want to define default values for options, you can do this by overriding theinterceptProperties
method (see Section 54.4, “Programming Model”).
ExampleJavadocHello.greetMe("Jane Doe")
with the following URI:
example://hello-javadoc/greetMe?name=Jane%20Doe
Default component instance
example
URI scheme to the default component instance, the Maven archetype creates the following file under the camel-api-example-component
sub-project:
src/main/resources/META-INF/services/org/apache/camel/component/example
example
URI scheme. Whenever you use an example://
URI in a route, Camel searches the classpath to look for the corresponding example
resource file. The example
file has the following contents:
class=org.jboss.fuse.example.ExampleComponent
ExampleComponent
component. The only time you would need to edit this file is if you refactor the name of the component class.
54.4. Programming Model
Overview
org.apache.camel.util.component
package. These base classes define some methods which you can (optionally) override when you are implementing your component. In this section, we provide a brief description of those methods and how you might use them in your own component implementation.
Component methods to implement
Component
class:
doStart()
- (Optional) A callback to create resources for the component during a cold start. An alternative approach is to adopt the strategy of lazy initialization (creating resources only when they are needed). In fact, lazy initialization is often the best strategy, so the
doStart
method is often not needed. doStop()
- (Optional) A callback to invoke code while the component is stopping. Stopping a component means that all of its resources are shut down, internal state is deleted, caches are cleared, and so on.NoteCamel guarantees that
doStop
is always called when the currentCamelContext
shuts down, even if the correspondingdoStart
was never called. doShutdown
- (Optional) A callback to invoke code while the
CamelContext
is shutting down. Whereas a stopped component can be restarted (with the semantics of a cold start), a component that gets shut down is completely finished. Hence, this callback represents the last chance to free up any resources belonging to the component.
What else to implement in the Component class?
Component
class is the natural place to hold references to objects that have the same (or similar) life cycle to the component object itself. For example, if a component uses OAuth security, it would be natural to hold references to the required OAuth objects in the Component
class and to define methods in the Component
class for creating the OAuth objects.
Endpoint methods to implement
Endpoint
class, as follows:
afterConfigureProperties()
- The main thing you need to do in this method is to create the appropriate type of proxy class (API class), to match the API name. The API name (which has already been extracted from the endpoint URI) is available either through the inherited
apiName
field or through thegetApiName
accessor. Typically, you would do a switch on theapiName
field to create the corresponding proxy class. For example:// Java private Object apiProxy; ... @Override protected void afterConfigureProperties() { // TODO create API proxy, set connection properties, etc. switch (apiName) { case HELLO_FILE: apiProxy = new ExampleFileHello(); break; case HELLO_JAVADOC: apiProxy = new ExampleJavadocHello(); break; default: throw new IllegalArgumentException("Invalid API name " + apiName); } }
getApiProxy(ApiMethod method, Map<String, Object> args)
- Override this method to return the proxy instance that you created in
afterConfigureProperties
. For example:@Override public Object getApiProxy(ApiMethod method, Map<String, Object> args) { return apiProxy; }
In special cases, you might want to make the choice of proxy dependent on the API method and arguments. ThegetApiProxy
gives you the flexibility to take this approach, if required. doStart()
- (Optional) A callback to create resources during a cold start. Has the same semantics as
Component.doStart()
. doStop()
- (Optional) A callback to invoke code while the component is stopping. Has the same semantics as
Component.doStop()
. doShutdown
- (Optional) A callback to invoke code while the component is shutting down. Has the same semantics as
Component.doShutdown()
. interceptPropertyNames(Set<String> propertyNames)
- (Optional) The API component framework uses the endpoint URI and supplied option values to determine which method to invoke (ambiguity could be due to overloading and aliases). If the component internally adds options or method parameters, however, the framework might need help in order to determine the right method to invoke. In this case, you must override the
interceptPropertyNames
method and add the extra (hidden or implicit) options to thepropertyNames
set. When the complete list of method parameters are provided in thepropertyNames
set, the framework will be able to identify the right method to invoke.NoteYou can override this method at the level of theEndpoint
,Producer
orConsumer
class. The basic rule is, if an option affects both producer endpoints and consumer endpoints, override the method in theEndpoint
class. interceptProperties(Map<String,Object> properties)
- (Optional) By overriding this method, you can modify or set the actual values of the options, before the API method is invoked. For example, you could use this method to set default values for some options, if necessary. In practice, it is often necessary to override both the
interceptPropertyNames
method and theinterceptProperty
method.NoteYou can override this method at the level of theEndpoint
,Producer
orConsumer
class. The basic rule is, if an option affects both producer endpoints and consumer endpoints, override the method in theEndpoint
class.
Consumer methods to implement
Consumer
class, as follows:
interceptPropertyNames(Set<String> propertyNames)
- (Optional) The semantics of this method are similar to
Endpoint.interceptPropertyNames
interceptProperties(Map<String,Object> properties)
- (Optional) The semantics of this method are similar to
Endpoint.interceptProperties
doInvokeMethod(Map<String, Object> args)
- (Optional) Overriding this method enables you to intercept the invocation of the Java API method. The most common reason for overriding this method is to customize the error handling around the method invocation. For example, a typical approach to overriding
doInvokeMethod
is shown in the following code fragment:// Java @Override protected Object doInvokeMethod(Map<String, Object> args) { try { return super.doInvokeMethod(args); } catch (RuntimeCamelException e) { // TODO - Insert custom error handling here! ... } }
You should invokedoInvokeMethod
on the super-class, at some point in this implementation, to ensure that the Java API method gets invoked. interceptResult(Object methodResult, Exchange resultExchange)
- (Optional) Do some additional processing on the result of the API method invocation. For example, you could add custom headers to the Camel exchange object,
resultExchange
, at this point. Object splitResult(Object result)
- (Optional) By default, if the result of the method API invocation is a
java.util.Collection
object or a Java array, the API component framework splits the result into multiple exchange objects (so that a single invocation result is converted into multiple messages).If you want to change the default behaviour, you can override thesplitResult
method in the consumer endpoint. Theresult
argument contains the result of the API message invocation. If you want to split the result, you should return an array type.NoteYou can also switch off the default splitting behaviour by settingconsumer.splitResult=false
on the endpoint URI.
Producer methods to implement
Producer
class, as follows:
interceptPropertyNames(Set<String> propertyNames)
- (Optional) The semantics of this method are similar to
Endpoint.interceptPropertyNames
interceptProperties(Map<String,Object> properties)
- (Optional) The semantics of this method are similar to
Endpoint.interceptProperties
doInvokeMethod(Map<String, Object> args)
- (Optional) The semantics of this method are similar to
Consumer.doInvokeMethod
. interceptResult(Object methodResult, Exchange resultExchange)
- (Optional) The semantics of this method are similar to
Consumer.interceptResult
.
Producer.splitResult()
method is never called, so it is not possible to split an API method result in the same way as you can for a consumer endpoint. To get a similar effect for a producer endpoint, you can use Camel's split()
DSL command (one of the standard enterprise integration patterns) to split Collection
or array results.
Consumer polling and threading model
54.5. Sample Component Implementations
Overview
Box.com
wadl2java
Maven plug-in to generate a Java API, which can then be wrapped using the API component framework.
GoogleDrive
doInvoke
method in the consumer and the producer.
Olingo2
Chapter 55. Configuring the API Component Maven Plug-In
Abstract
55.1. Overview of the Plug-In Configuration
Overview
camel-api-component-maven-plugin
, is to generate the API mapping classes, which implement the mapping between endpoint URIs and API method invocations. By editing the configuration of the API component Maven plug-in, you can customize various aspects of the API mapping.
Location of the generated code
ProjectName-component/target/generated-sources/camel-component
Prerequisites
provided
scope).
Setting up the plug-in
ProjectName-component/pom.xml
file, which you can then customize for your project. The main aspects of the plug-in set-up are, as follows:
- Maven dependencies must be declared for the requisite Java API and for the Javadoc metadata.
- The plug-in's base configuration is declared in the
pluginManagement
scope (which also defines the version of the plug-in to use). - The plug-in instance itself is declared and configured.
- The
build-helper-maven
plug-in is configured to pick up the generated sources from thetarget/generated-sources/camel-component
directory and include them in the Maven build.
Example base configuration
pluginManagement
scope when the code has been generated using the API component archetype:
<?xml version="1.0" encoding="UTF-8"?> <project ...> ... <build> ... <pluginManagement> <plugins> <plugin> <groupId>org.apache.camel</groupId> <artifactId>camel-api-component-maven-plugin</artifactId> <version>2.15.1.redhat-620133</version> <configuration> <scheme>${schemeName}</scheme> <componentName>${componentName}</componentName> <componentPackage>${componentPackage}</componentPackage> <outPackage>${outPackage}</outPackage> </configuration> </plugin> </plugins> </pluginManagement> ... </build> ... </project
pluginManagement
scope provides default settings for the plug-in. It does not actually create an instance of a plug-in, but its default settings will be used by any API component plug-in instance.
Base configuration
version
element), the preceding base configuration specifies the following configuration properties:
scheme
- The URI scheme for this API component.
componentName
- The name of this API component (which is also used as a prefix for generated class names).
componentPackage
- Specifies the Java package containing the classes generated by the API component Maven archetype. This package is also exported by the default
maven-bundle-plugin
configuration. Hence, if you want a class to be publicly visible, you should place it in this Java package. outPackage
- Specifies the Java package where the generated API mapping classes are placed (when they are generated by the API component Maven plug-in). By default, this has the value of the
componentName
property, with the addition of the.internal
suffix. This package is declared as private by the defaultmaven-bundle-plugin
configuration. Hence, if you want a class to be private, you should place it in this Java package.
Example instance configuration
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> ... <build> <defaultGoal>install</defaultGoal> <plugins> ... <!-- generate Component source and test source --> <plugin> <groupId>org.apache.camel</groupId> <artifactId>camel-api-component-maven-plugin</artifactId> <executions> <execution> <id>generate-test-component-classes</id> <goals> <goal>fromApis</goal> </goals> <configuration> <apis> <api> <apiName>hello-file</apiName> <proxyClass>org.jboss.fuse.example.api.ExampleFileHello</proxyClass> <fromSignatureFile>signatures/file-sig-api.txt</fromSignatureFile> </api> <api> <apiName>hello-javadoc</apiName> <proxyClass>org.jboss.fuse.example.api.ExampleJavadocHello</proxyClass> <fromJavadoc/> </api> </apis> </configuration> </execution> </executions> </plugin> ... </plugins> ... </build> ... </project>
Basic mapping configuration
configuration
element, which contains a single apis
child element to configure the classes of the Java API. Each API class is configured by an api
element, as follows:
apiName
- The API name is a short name for the API class and is used as the
endpoint-prefix
part of an endpoint URI.NoteIf the API consists of just a single Java class, you can leave theapiName
element empty, so that theendpoint-prefix
becomes redundant, and you can then specify the endpoint URI using the format shown in the section called “URI format for a single API class”. proxyClass
- This element specifies the fully-qualified name of the API class.
fromJavadoc
- If the API class is accompanied by Javadoc metadata, you must indicate this by including the
fromJavadoc
element and the Javadoc itself must also be specified in the Maven file, as aprovided
dependency. fromSignatureFile
- If the API class is accompanied by signature file metadata, you must indicate this by including the
fromSignatureFile
element, where the content of this element specifies the location of the signature file.NoteThe signature files do not get included in the final package built by Maven, because these files are needed only at build time, not at run time.
Customizing the API mapping
- Method aliases—you can define additional names (aliases) for an API method using the
aliases
configuration element. For details, see Section 55.3, “Method Aliases”. - Nullable options—you can use the
nullableOptions
configuration element to declare method arguments that default tonull
. For details, see Section 55.4, “Nullable Options”. - Argument name substitution—due to the way the API mapping is implemented, the arguments from all of the methods in a particular API class belong to the same namespace. If two arguments with the same name are declared to be of different type, this leads to a clash. To avoid such name clashes, you can use the
substitutions
configuration element to rename method arguments (as they would appear in a URI). For details, see Section 55.5, “Argument Name Substitution”. - Excluding arguments—when it comes to mapping Java arguments to URI options, you might sometimes want to exclude certain arguments from the mapping. You can filter out unwanted arguments by specifying either the
excludeConfigNames
element or theexcludeConfigTypes
element. For details, see Section 55.6, “Excluded Arguments”. - Extra options—sometimes you might want to define extra options, which are not part of the Java API. You can do this using the
extraOptions
configuration element.
Configuring Javadoc metadata
Configuring signature file metadata
fromSignatureFile
is used to specify the location of the corresponding signature file. It has no special options.
55.2. Javadoc Options
Overview
fromJavadoc
element with no options. But in cases where you do not want to include the entire Java API in your API mapping, you can filter the Javadoc metadata to customize the content. In other words, because the API component Maven plug-in generates the API mapping by iterating over the Javadoc metadata, it is possible to customize the scope of the generated API mapping by filtering out unwanted parts of the Javadoc metadata.
Syntax
fromJavadoc
element can be configured with optional child elements, as follows:
<fromJavadoc> <excludePackages>PackageNamePattern</excludePackages> <excludeClasses>ClassNamePattern</excludeClasses> <excludeMethods>MethodNamePattern</excludeMethods> <includeMethods>MethodNamePattern</includeMethods> <includeStaticMethods>[true|false]<includeStaticMethods> </fromJavadoc>
Scope
fromJavadoc
element can optionally appear as a child of the apis
element and/or as a child of api
elements:
<configuration> <apis> <api> <apiName>...</apiName> ... <fromJavadoc>...</fromJavadoc> </api> <fromJavadoc>...</fromJavadoc> ... </apis> </configuration>
fromJavadoc
element at the following scopes:
- As a child of an
api
element—thefromJavadoc
options apply only to the API class specified by theapi
element. - As a child of the
apis
element—thefromJavadoc
options apply to all API classes by default, but can be overridden at theapi
level.
Options
fromJavadoc
:
excludePackages
- Specifies a regular expression (
java.util.regex
syntax) for excluding Java packages from the API mapping model. All package names that match the regular expression are excluded; and all classes derived from the excluded classes are also ignored. Default value isjavax?\.lang.*
. excludeClasses
- Specifies a regular expression (
java.util.regex
syntax) for excluding API base classes from the API mapping. All class names that match the regular expression are excluded; and all classes derived from the excluded classes are also ignored. excludeMethods
- Specifies a regular expression (
java.util.regex
syntax) for excluding methods from the API mapping model. includeMethods
- Specifies a regular expression (
java.util.regex
syntax) for including methods from the API mapping model. includeStaticMethods
- If
true
, static methods will also be included in the API mapping model. Default isfalse
.
55.3. Method Aliases
Overview
widget
) to be used as an alias for an accessor method (such as getWidget
or setWidget
).
Syntax
aliases
element can be defined with one or more alias
child elements, as follows:
<aliases> <alias> <methodPattern>MethodPattern</methodPattern> <methodAlias>Alias</methodAlias> </alias> ... </aliases>
MethodPattern
is a regular expression (java.util.regex
syntax) for matching method names from the Java API, and the pattern typically includes capturing groups. The Alias
is the replacement expression (for use in a URI), which can use the text from the preceding capturing groups (for example, specified as $1
, $2
, or $3
for the text from the first, second, or third capturing group).
Scope
aliases
element can optionally appear as a child of the apis
element and/or as a child of api
elements:
<configuration> <apis> <api> <apiName>...</apiName> ... <aliases>...</aliases> </api> <aliases>...</aliases> ... </apis> </configuration>
aliases
element at the following scopes:
- As a child of an
api
element—thealiases
mappings apply only to the API class specified by theapi
element. - As a child of the
apis
element—thealiases
mappings apply to all API classes by default, but can be overridden at theapi
level.
Example
<aliases> <alias> <methodPattern>[gs]et(.+)</methodPattern> <methodAlias>$1</methodAlias> </alias> </aliases>
widget
as an alias for either of the methods getWidget
or setWidget
. Note the use of a capturing group, (.+)
, to capture the latter part of the method name (for example, Widget
).
55.4. Nullable Options
Overview
null
. But this is not allowed by default. If you want to allow some of your method arguments from the Java API to take null
values, you must declare this explicitly using the nullableOptions
element.
Syntax
nullableOptions
element can be defined with one or more nullableOption
child elements, as follows:
<nullableOptions> <nullableOption>ArgumentName</nullableOption> ... </nullableOptions>
ArgumentName
is the name of a method argument from the Java API.
Scope
nullableOptions
element can optionally appear as a child of the apis
element and/or as a child of api
elements:
<configuration> <apis> <api> <apiName>...</apiName> ... <nullableOptions>...</nullableOptions> </api> ... <nullableOptions>...</nullableOptions> </apis> </configuration>
nullableOptions
element at the following scopes:
- As a child of an
api
element—thenullableOptions
mappings apply only to the API class specified by theapi
element. - As a child of the
apis
element—thenullableOptions
mappings apply to all API classes by default, but can be overridden at theapi
level.
Example
CompaniesResource
proxy class from the Apache Camel LinkedIn component:
<nullableOptions> <nullableOption>companySizes</nullableOption> <nullableOption>count</nullableOption> <nullableOption>email_domain</nullableOption> <nullableOption>end_timestamp</nullableOption> <nullableOption>event_type</nullableOption> <nullableOption>geos</nullableOption> <nullableOption>industries</nullableOption> <nullableOption>is_company_admin</nullableOption> <nullableOption>jobFunc</nullableOption> <nullableOption>secure_urls</nullableOption> <nullableOption>seniorities</nullableOption> <nullableOption>start</nullableOption> <nullableOption>start_timestamp</nullableOption> <nullableOption>statistics_update_key</nullableOption> <nullableOption>time_granularity</nullableOption> </nullableOptions>
55.5. Argument Name Substitution
Overview
public void doSomething(int id, String name); public void doSomethingElse(int id, String name);
camel-api-component-maven-plugin
generates the configuration class, ProxyClassEndpointConfiguration
, which contains getter and setter methods for all of the arguments in the ProxyClass
class. For example, given the preceding methods, the plug-in would generate the following getter and setter methods in the configuration class:
public int getId(); public void setId(int id); public String getName(); public void setName(String name);
id
argument appears multiple times as different types, as in the following example:
public void doSomething(int id, String name); public void doSomethingElse(int id, String name); public String lookupByID(String id);
getId
method that returns int
and a getId
method that returns String
in the same scope. The solution to this problem is to use argument name substitution to customize the mapping of argument names to URI option names.
Syntax
substitutions
element can be defined with one or more substitution
child elements, as follows:
<substitutions> <substitution> <method>MethodPattern</method> <argName>ArgumentNamePattern</argName> <argType>TypeNamePattern</argType> <replacement>SubstituteArgName</replacement> <replaceWithType>[true|false]</replaceWithType> </substitution> ... </substitutions>
argType
element and the replaceWithType
element are optional and can be omitted.
Scope
substitutions
element can optionally appear as a child of the apis
element and/or as a child of api
elements:
<configuration> <apis> <api> <apiName>...</apiName> ... <substitutions>...</substitutions> </api> <substitutions>...</substitutions> ... </apis> </configuration>
substitutions
element at the following scopes:
- As a child of an
api
element—thesubstitutions
apply only to the API class specified by theapi
element. - As a child of the
apis
element—thesubstitutions
apply to all API classes by default, but can be overridden at theapi
level.
Child elements
substitution
element can be defined with the following child elements:
method
- Specifies a regular expression (
java.util.regex
syntax) to match a method name from the Java API. argName
- Specifies a regular expression (
java.util.regex
syntax) to match an argument name from the matched method, where the pattern typically includes capturing groups. argType
- (Optional) Specifies a regular expression (
java.util.regex
syntax) to match the type of the argument. If you set thereplaceWithType
option totrue
, you would typically use capturing groups in this regular expression. replacement
- Given a particular match of the
method
pattern,argName
pattern, and (optionally)argType
pattern, thereplacement
element defines the substitute argument name (for use in a URI). The replacement text can be constructed using strings captured from theargName
regular expression pattern (using the syntax,$1
,$2
,$3
to insert the first, second, or third capturing group, respectively). Alternatively, the replacement text can be constructed using strings captured from theargType
regular expression pattern, if you set thereplaceWithType
option totrue
. replaceWithType
- When
true
, specifies that the replacement text is constructed using strings captured from theargType
regular expression. Defaults tofalse
.
Example
java.lang.String
type, by adding the suffix, Param
to the argument name:
<substitutions> <substitution> <method>^.+$</method> <argName>^.+$</argName> <argType>java.lang.String</argType> <replacement>$1Param</replacement> <replaceWithType>false</replaceWithType> </substitution> </substitutions>
public String greetUs(String name1, String name2);
name1Param
and name2Param
, in the endpoint URI.
55.6. Excluded Arguments
Overview
excludeConfigNames
element or the excludeConfigTypes
element in the camel-api-component-maven-plugin
plug-in configuration.
Syntax
excludeConfigNames
element and the excludeConfigTypes
element are specified as follows:
<excludeConfigNames>ArgumentNamePattern</excludeConfigNames> <excludeConfigTypes>TypeNamePattern</excludeConfigTypes>
ArgumentNamePattern
and TypeNamePattern
are regular expressions that match the argument name and the argument type, respectively.
Scope
excludeConfigNames
element and the excludeConfigTypes
element can optionally appear as children of the apis
element and/or as children of api
elements:
<configuration> <apis> <api> <apiName>...</apiName> ... <excludeConfigNames>...</excludeConfigNames> <excludeConfigTypes>...</excludeConfigTypes> </api> <excludeConfigNames>...</excludeConfigNames> <excludeConfigTypes>...</excludeConfigTypes> ... </apis> </configuration>
excludeConfigNames
element and the excludeConfigTypes
element at the following scopes:
- As a child of an
api
element—the exclusions apply only to the API class specified by theapi
element. - As a child of the
apis
element—the exclusions apply to all API classes by default, but can be overridden at theapi
level.
Elements
excludeConfigNames
- Specifies a regular expression (
java.util.regex
syntax) for excluding arguments, based on matching the argument name. excludeConfigTypes
- Specifies a regular expression (
java.util.regex
syntax) for excluding arguments, based on matching the argument type.
55.7. Extra Options
Overview
extraOptions
options are usually used to either compute or hide complex API parameters by providing simpler options instead. For example, the API method might take a POJO option, that could be provided more easily as parts of the POJO in the URI. The component could do this by adding the parts as extra options, and creating the POJO parameter internally. To complete the implementation of these extra options, you also need to override the interceptProperties
method in the EndpointConsumer
and/or EndpointProducer
classes (see Section 54.4, “Programming Model”).
Syntax
extraOptions
element can be defined with one or more extraOption
child elements, as follows:
<extraOptions> <extraOption> <type>TypeName</type> <name>OptionName</name> </extraOption> </extraOptions>
TypeName
is the fully-qualified type name of the extra option and OptionName
is the name of the extra URI option.
Scope
extraOptions
element can optionally appear as a child of the apis
element and/or as a child of api
elements:
<configuration> <apis> <api> <apiName>...</apiName> ... <extraOptions>...</extraOptions> </api> <extraOptions>...</extraOptions> ... </apis> </configuration>
extraOptions
element at the following scopes:
- As a child of an
api
element—theextraOptions
apply only to the API class specified by theapi
element. - As a child of the
apis
element—theextraOptions
apply to all API classes by default, but can be overridden at theapi
level.
Child elements
extraOptions
element can be defined with the following child elements:
type
- Specifies the fully-qualified type name of the extra option.
name
- Specifies the option name, as it would appear in an endpoint URI.
Example
customOption
, which is of java.util.list<String>
type:
<extraOptions> <extraOption> <type>java.util.List<String></type> <name>customOption</name> </extraOption> </extraOptions>
Index
Symbols
- @Converter, Implement an annotated converter class
A
- AsyncCallback, Asynchronous processing
- asynchronous producer
- implementing, How to implement an asynchronous producer
- AsyncProcessor, Asynchronous processing
- auto-discovery
- configuration, Configuring auto-discovery
C
- Component
- createEndpoint(), URI parsing
- definition, The Component interface
- methods, Component methods
- component prefix, Component
- components, Component
- bean properties, Define bean properties on your component class
- configuring, Installing and configuring the component
- implementation steps, Implementation steps
- installing, Installing and configuring the component
- interfaces to implement, Which interfaces do you need to implement?
- parameter injection, Parameter injection
- Spring configuration, Configure the component in Spring
- Consumer, Consumer
- consumers, Consumer
- event-driven, Event-driven pattern, Implementation steps
- polling, Polling pattern, Implementation steps
- scheduled, Scheduled poll pattern, Implementation steps
- threading, Overview
D
- DefaultComponent
- createEndpoint(), URI parsing
- DefaultEndpoint, Event-driven endpoint implementation
- createExchange(), Event-driven endpoint implementation
- createPollingConsumer(), Event-driven endpoint implementation
- getCamelConext(), Event-driven endpoint implementation
- getComponent(), Event-driven endpoint implementation
- getEndpointUri(), Event-driven endpoint implementation
E
- Endpoint, Endpoint
- createConsumer(), Endpoint methods
- createExchange(), Endpoint methods
- createPollingConsumer(), Endpoint methods
- createProducer(), Endpoint methods
- getCamelContext(), Endpoint methods
- getEndpointURI(), Endpoint methods
- interface definition, The Endpoint interface
- isLenientProperties(), Endpoint methods
- isSingleton(), Endpoint methods
- setCamelContext(), Endpoint methods
- endpoint
- event-driven, Event-driven endpoint implementation
- scheduled, Scheduled poll endpoint implementation
- endpoints, Endpoint
- Exchange, Exchange, The Exchange interface
- copy(), Exchange methods
- getExchangeId(), Exchange methods
- getIn(), Accessing message headers, Exchange methods
- getOut(), Exchange methods
- getPattern(), Exchange methods
- getProperties(), Exchange methods
- getProperty(), Exchange methods
- getUnitOfWork(), Exchange methods
- removeProperty(), Exchange methods
- setExchangeId(), Exchange methods
- setIn(), Exchange methods
- setOut(), Exchange methods
- setProperty(), Exchange methods
- setUnitOfWork(), Exchange methods
- exchange
- in capable, Testing the exchange pattern
- out capable, Testing the exchange pattern
- exchange properties
- accessing, Wrapping the exchange accessors
- ExchangeHelper, The ExchangeHelper Class
- getContentType(), Get the In message's MIME content type
- getMandatoryHeader(), Accessing message headers, Wrapping the exchange accessors
- getMandatoryInBody(), Wrapping the exchange accessors
- getMandatoryOutBody(), Wrapping the exchange accessors
- getMandatoryProperty(), Wrapping the exchange accessors
- isInCapable(), Testing the exchange pattern
- isOutCapable(), Testing the exchange pattern
- resolveEndpoint(), Resolve an endpoint
- exchanges, Exchange
I
- in message
- MIME type, Get the In message's MIME content type
M
- Message, Message
- getHeader(), Accessing message headers
- message headers
- accessing, Accessing message headers
- messages, Message
P
- performer, Overview
- pipeline, Pipelining model
- Processor, Processor interface
- implementing, Implementing the Processor interface
- producer, Producer
- Producer, Producer
- createExchange(), Producer methods
- getEndpoint(), Producer methods
- process(), Producer methods
- producers
- asynchronous, Asynchronous producer
- synchronous, Synchronous producer
S
- ScheduledPollEndpoint, Scheduled poll endpoint implementation
- simple processor
- implementing, Implementing the Processor interface
- synchronous producer
- implementing, How to implement a synchronous producer
T
- type conversion
- runtime process, Type conversion process
- type converter
- annotating the implementation, Implement an annotated converter class
- discovery file, Create a TypeConverter file
- implementation steps, How to implement a type converter
- mater, Master type converter
- packaging, Package the type converter
- slave, Master type converter
- TypeConverter, Type converter interface
- TypeConverterLoader, Type converter loader
U
- useIntrospectionOnEndpoint(), Disabling endpoint parameter injection
W
- wire tap pattern, System Management
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