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Chapter 67. CometD Component

Available as of Camel version 2.0

The cometd: component is a transport for working with the jetty implementation of the cometd/bayeux protocol.
Using this component in combination with the dojo toolkit library it’s possible to push Camel messages directly into the browser using an AJAX based mechanism.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-cometd</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

67.1. URI format

cometd://host:port/channelName[?options]

The channelName represents a topic that can be subscribed to by the Camel endpoints.

67.2. Examples

cometd://localhost:8080/service/mychannel
cometds://localhost:8443/service/mychannel

where cometds: represents an SSL configured endpoint.

67.3. Options

The CometD component supports 8 options which are listed below.

Name	Description	Default	Type
sslKeyPassword (security)	The password for the keystore when using SSL.		String
sslPassword (security)	The password when using SSL.		String
sslKeystore (security)	The path to the keystore.		String
securityPolicy (security)	To use a custom configured SecurityPolicy to control authorization		SecurityPolicy
extensions (common)	To use a list of custom BayeuxServer.Extension that allows modifying incoming and outgoing requests.		List
sslContextParameters (security)	To configure security using SSLContextParameters		SSLContextParameters
useGlobalSslContext Parameters (security)	Enable usage of global SSL context parameters.	false	boolean
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 CometD endpoint is configured using URI syntax:

cometd:host:port/channelName

with the following path and query parameters:

67.3.1. Path Parameters (3 parameters):

Name	Description	Type
host	Required Hostname	String
port	Required Host port number	int
channelName	Required The channelName represents a topic that can be subscribed to by the Camel endpoints.	String

67.3.2. Query Parameters (16 parameters):

Name	Description	Default	Type
allowedOrigins (common)	The origins domain that support to cross, if the crosssOriginFilterOn is true	*	String
baseResource (common)	The root directory for the web resources or classpath. Use the protocol file: or classpath: depending if you want that the component loads the resource from file system or classpath. Classpath is required for OSGI deployment where the resources are packaged in the jar		String
crossOriginFilterOn (common)	If true, the server will support for cross-domain filtering	false	boolean
filterPath (common)	The filterPath will be used by the CrossOriginFilter, if the crosssOriginFilterOn is true		String
interval (common)	The client side poll timeout in milliseconds. How long a client will wait between reconnects		int
jsonCommented (common)	If true, the server will accept JSON wrapped in a comment and will generate JSON wrapped in a comment. This is a defence against Ajax Hijacking.	true	boolean
logLevel (common)	Logging level. 0=none, 1=info, 2=debug.	1	int
maxInterval (common)	The max client side poll timeout in milliseconds. A client will be removed if a connection is not received in this time.	30000	int
multiFrameInterval (common)	The client side poll timeout, if multiple connections are detected from the same browser.	1500	int
timeout (common)	The server side poll timeout in milliseconds. This is how long the server will hold a reconnect request before responding.	240000	int
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
sessionHeadersEnabled (consumer)	Whether to include the server session headers in the Camel message when creating a Camel Message for incoming requests.	false	boolean
exceptionHandler (consumer)	To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this options 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
disconnectLocalSession (producer)	Whether to disconnect local sessions after publishing a message to its channel. Disconnecting local session is needed as they are not swept by default by CometD, and therefore you can run out of memory.	false	boolean
synchronous (advanced)	Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).	false	boolean

You can append query options to the URI in the following format, ?option=value&option=value&…

Here is some examples on How to pass the parameters

For file (for webapp resources located in the Web Application directory -→ cometd://localhost:8080?resourceBase=file./webapp
For classpath (when by example the web resources are packaged inside the webapp folder -→ cometd://localhost:8080?resourceBase=classpath:webapp

67.4. Authentication

Available as of Camel 2.8

You can configure custom SecurityPolicy and Extension’s to the `CometdComponent which allows you to use authentication as documented here

67.5. Setting up SSL for Cometd Component

67.5.1. Using the JSSE Configuration Utility

As of Camel 2.9, the Cometd component supports SSL/TLS configuration through the Camel JSSE Configuration Utility. This utility greatly decreases the amount of component specific code you need to write and is configurable at the endpoint and component levels. The following examples demonstrate how to use the utility with the Cometd component. You need to configure SSL on the CometdComponent.

Programmatic configuration of the component

KeyStoreParameters ksp = new KeyStoreParameters();
ksp.setResource("/users/home/server/keystore.jks");
ksp.setPassword("keystorePassword");

KeyManagersParameters kmp = new KeyManagersParameters();
kmp.setKeyStore(ksp);
kmp.setKeyPassword("keyPassword");

TrustManagersParameters tmp = new TrustManagersParameters();
tmp.setKeyStore(ksp);

SSLContextParameters scp = new SSLContextParameters();
scp.setKeyManagers(kmp);
scp.setTrustManagers(tmp);

CometdComponent commetdComponent = getContext().getComponent("cometds", CometdComponent.class);
commetdComponent.setSslContextParameters(scp);

Spring DSL based configuration of endpoint

...
  <camel:sslContextParameters
      id="sslContextParameters">
    <camel:keyManagers
        keyPassword="keyPassword">
      <camel:keyStore
          resource="/users/home/server/keystore.jks"
          password="keystorePassword"/>
    </camel:keyManagers>
    <camel:trustManagers>
      <camel:keyStore
          resource="/users/home/server/keystore.jks"
          password="keystorePassword"/>
    </camel:keyManagers>
  </camel:sslContextParameters>...
 
  <bean id="cometd" class="org.apache.camel.component.cometd.CometdComponent">
    <property name="sslContextParameters" ref="sslContextParameters"/>
  </bean>
...
  <to uri="cometds://127.0.0.1:443/service/test?baseResource=file:./target/test-classes/webapp&timeout=240000&interval=0&maxInterval=30000&multiFrameInterval=1500&jsonCommented=true&logLevel=2"/>...

67.6. See Also

Configuring Camel
Component
Endpoint
Getting Started