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Chapter 377. XQuery Component

Available as of Camel version 1.0

Camel supports XQuery to allow an Expression or Predicate to be used in the DSL or Xml Configuration. For example you could use XQuery to create an Predicate in a Message Filter or as an Expression for a Recipient List.

377.1. Options

The XQuery component supports 4 options, which are listed below.

NameDescriptionDefaultType

moduleURIResolver (advanced)

To use the custom ModuleURIResolver

 

ModuleURIResolver

configuration (advanced)

To use a custom Saxon configuration

 

Configuration

configurationProperties (advanced)

To set custom Saxon configuration properties

 

Map

resolveProperty Placeholders (advanced)

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

boolean

The XQuery endpoint is configured using URI syntax: 

xquery:resourceUri

with the following path and query parameters:

377.1.1. Path Parameters (1 parameters):

NameDescriptionDefaultType

resourceUri

Required The name of the template to load from classpath or file system

 

String

377.1.2. Query Parameters (31 parameters):

NameDescriptionDefaultType

allowStAX (common)

Whether to allow using StAX mode

false

boolean

headerName (common)

To use a Camel Message header as the input source instead of Message body.

 

String

namespacePrefixes (common)

Allows to control which namespace prefixes to use for a set of namespace mappings

 

Map

resultsFormat (common)

What output result to use

DOM

ResultFormat

resultType (common)

What output result to use defined as a class

 

Class

stripsAllWhiteSpace (common)

Whether to strip all whitespaces

true

boolean

bridgeErrorHandler (consumer)

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored.

false

boolean

sendEmptyMessageWhenIdle (consumer)

If the polling consumer did not poll any files, you can enable this option to send an empty message (no body) instead.

false

boolean

exceptionHandler (consumer)

To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored.

 

ExceptionHandler

exchangePattern (consumer)

Sets the exchange pattern when the consumer creates an exchange.

 

ExchangePattern

pollStrategy (consumer)

A pluggable org.apache.camel.PollingConsumerPollingStrategy allowing you to provide your custom implementation to control error handling usually occurred during the poll operation before an Exchange have been created and being routed in Camel.

 

PollingConsumerPoll Strategy

configuration (advanced)

To use a custom Saxon configuration

 

Configuration

configurationProperties (advanced)

To set custom Saxon configuration properties

 

Map

moduleURIResolver (advanced)

To use the custom ModuleURIResolver

 

ModuleURIResolver

parameters (advanced)

Additional parameters

 

Map

properties (advanced)

Properties to configure the serialization parameters

 

Properties

staticQueryContext (advanced)

To use a custom Saxon StaticQueryContext

 

StaticQueryContext

synchronous (advanced)

Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).

false

boolean

backoffErrorThreshold (scheduler)

The number of subsequent error polls (failed due some error) that should happen before the backoffMultipler should kick-in.

 

int

backoffIdleThreshold (scheduler)

The number of subsequent idle polls that should happen before the backoffMultipler should kick-in.

 

int

backoffMultiplier (scheduler)

To let the scheduled polling consumer backoff if there has been a number of subsequent idles/errors in a row. The multiplier is then the number of polls that will be skipped before the next actual attempt is happening again. When this option is in use then backoffIdleThreshold and/or backoffErrorThreshold must also be configured.

 

int

delay (scheduler)

Milliseconds before the next poll. You can also specify time values using units, such as 60s (60 seconds), 5m30s (5 minutes and 30 seconds), and 1h (1 hour).

500

long

greedy (scheduler)

If greedy is enabled, then the ScheduledPollConsumer will run immediately again, if the previous run polled 1 or more messages.

false

boolean

initialDelay (scheduler)

Milliseconds before the first poll starts. You can also specify time values using units, such as 60s (60 seconds), 5m30s (5 minutes and 30 seconds), and 1h (1 hour).

1000

long

runLoggingLevel (scheduler)

The consumer logs a start/complete log line when it polls. This option allows you to configure the logging level for that.

TRACE

LoggingLevel

scheduledExecutorService (scheduler)

Allows for configuring a custom/shared thread pool to use for the consumer. By default each consumer has its own single threaded thread pool.

 

ScheduledExecutor Service

scheduler (scheduler)

To use a cron scheduler from either camel-spring or camel-quartz2 component

none

ScheduledPollConsumer Scheduler

schedulerProperties (scheduler)

To configure additional properties when using a custom scheduler or any of the Quartz2, Spring based scheduler.

 

Map

startScheduler (scheduler)

Whether the scheduler should be auto started.

true

boolean

timeUnit (scheduler)

Time unit for initialDelay and delay options.

MILLISECONDS

TimeUnit

useFixedDelay (scheduler)

Controls if fixed delay or fixed rate is used. See ScheduledExecutorService in JDK for details.

true

boolean

377.2. Spring Boot Auto-Configuration

The component supports 8 options, which are listed below.

NameDescriptionDefaultType

camel.component.xquery.configuration

To use a custom Saxon configuration. The option is a net.sf.saxon.Configuration type.

 

String

camel.component.xquery.configuration-properties

To set custom Saxon configuration properties

 

Map

camel.component.xquery.enabled

Enable xquery component

true

Boolean

camel.component.xquery.module-u-r-i-resolver

To use the custom ModuleURIResolver. The option is a net.sf.saxon.lib.ModuleURIResolver type.

 

String

camel.component.xquery.resolve-property-placeholders

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

Boolean

camel.language.xquery.enabled

Enable xquery language

true

Boolean

camel.language.xquery.trim

Whether to trim the value to remove leading and trailing whitespaces and line breaks

true

Boolean

camel.language.xquery.type

Sets the class name of the result type (type from output) The default result type is NodeSet

 

String

377.3. Examples

from("queue:foo").filter().
  xquery("//foo").
  to("queue:bar")

You can also use functions inside your query, in which case you need an explicit type conversion (or you will get a org.w3c.dom.DOMException: HIERARCHY_REQUEST_ERR) by passing the Class as a second argument to the xquery() method. 

from("direct:start").
  recipientList().xquery("concat('mock:foo.', /person/@city)", String.class);

377.4. Variables

The IN message body will be set as the contextItem. Besides this these Variables is also added as parameters:

VariableTypeDescription

exchange

Exchange

The current Exchange

in.body

Object

The In message’s body

out.body

Object

The OUT message’s body (if any)

in.headers.*

Object

You can access the value of exchange.in.headers with key foo by using the variable which name is in.headers.foo

out.headers.*

Object

You can access the value of exchange.out.headers with key foo by using the variable which name is out.headers.foo variable

key name

Object

Any exchange.properties and exchange.in.headers and any additional parameters set using setParameters(Map). These parameters is added with they own key name, for instance if there is an IN header with the key name foo then its added as foo.

377.5. Using XML configuration

If you prefer to configure your routes in your Spring XML file then you can use XPath expressions as follows 

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:foo="http://example.com/person"
       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">

  <camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
    <route>
      <from uri="activemq:MyQueue"/>
      <filter>
        <xquery>/foo:person[@name='James']</xquery>
        <to uri="mqseries:SomeOtherQueue"/>
      </filter>
    </route>
  </camelContext>
</beans>

Notice how we can reuse the namespace prefixes, foo in this case, in the XPath expression for easier namespace based XQuery expressions!

When you use functions in your XQuery expression you need an explicit type conversion which is done in the xml configuration via the @type attribute: 

    <xquery type="java.lang.String">concat('mock:foo.', /person/@city)</xquery>

377.6. Using XQuery as transformation

We can do a message translation using transform or setBody in the route, as shown below: 

from("direct:start").
   transform().xquery("/people/person");

Notice that xquery will use DOMResult by default, so if we want to grab the value of the person node, using text() we need to tell xquery to use String as result type, as shown: 

from("direct:start").
   transform().xquery("/people/person/text()", String.class);

377.7. Using XQuery as an endpoint

Sometimes an XQuery expression can be quite large; it can essentally be used for Templating. So you may want to use an XQuery Endpoint so you can route using XQuery templates.

The following example shows how to take a message of an ActiveMQ queue (MyQueue) and transform it using XQuery and send it to MQSeries. 

  <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
    <route>
      <from uri="activemq:MyQueue"/>
      <to uri="xquery:com/acme/someTransform.xquery"/>
      <to uri="mqseries:SomeOtherQueue"/>
    </route>
  </camelContext>

Currently custom functions in XQuery might result in a NullPointerException (Camel 2.18, 2.19 and 2.20). This is expected to be fixed in Camel 2.21

377.8. Examples

Here is a simple example using an XQuery expression as a predicate in a Message Filter

This example uses XQuery with namespaces as a predicate in a Message Filter

377.9. Learning XQuery

XQuery is a very powerful language for querying, searching, sorting and returning XML. For help learning XQuery try these tutorials

You might also find the XQuery function reference useful

377.10. Loading script from external resource

Available as of Camel 2.11

You can externalize the script and have Camel load it from a resource such as "classpath:", "file:", or "http:".
This is done using the following syntax: "resource:scheme:location", eg to refer to a file on the classpath you can do: 

.setHeader("myHeader").xquery("resource:classpath:myxquery.txt", String.class)

377.11. Dependencies

To use XQuery in your camel routes you need to add the a dependency on camel-saxon which implements the XQuery language.

If you use maven you could just add the following to your pom.xml, substituting the version number for the latest & greatest release (see the download page for the latest versions). 

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-saxon</artifactId>
  <version>x.x.x</version>
</dependency>
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