CometD

Since Camel 2.0

Both producer and consumer are supported

The Cometd component is a transport mechanism 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>

URI format

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

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

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

where cometds: represents an SSL configured endpoint.

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

At the component level, you set general and shared configurations that are, then, inherited by the endpoints. It is the highest configuration level.

For example, a component may have security settings, credentials for authentication, urls for network connection and so forth.

Some components only have a few options, and others may have many. Because components typically have pre-configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all.

You can configure components using:

  • the Component DSL.

  • in a configuration file (application.properties, *.yaml files, etc).

  • directly in the Java code.

Configuring Endpoint Options

You usually spend more time setting up endpoints because they have many options. These options help you customize what you want the endpoint to do. The options are also categorized into whether the endpoint is used as a consumer (from), as a producer (to), or both.

Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL and DataFormat DSL as a type safe way of configuring endpoints and data formats in Java.

A good practice when configuring options is to use Property Placeholders.

Property placeholders provide a few benefits:

  • They help prevent using hardcoded urls, port numbers, sensitive information, and other settings.

  • They allow externalizing the configuration from the code.

  • They help the code to become more flexible and reusable.

The following two sections list all the options, firstly for the component followed by the endpoint.

Component Options

The CometD component supports 10 options, which are listed below.

Name Description Default Type

bridgeErrorHandler (consumer)

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. 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

lazyStartProducer (producer)

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

autowiredEnabled (advanced)

Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc.

true

boolean

extensions (advanced)

To use a list of custom BayeuxServer.Extension that allows modifying incoming and outgoing requests.

List

securityPolicy (security)

To use a custom configured SecurityPolicy to control authorization.

SecurityPolicy

sslContextParameters (security)

To configure security using SSLContextParameters.

SSLContextParameters

sslKeyPassword (security)

The password for the keystore when using SSL.

String

sslKeystore (security)

The path to the keystore.

String

sslPassword (security)

The password when using SSL.

String

useGlobalSslContextParameters (security)

Enable usage of global SSL context parameters.

false

boolean

Endpoint Options

The CometD endpoint is configured using URI syntax:

cometd:host:port/channelName

With the following path and query parameters:

Path Parameters (3 parameters)

Name Description Default Type

host (common)

Required Hostname.

String

port (common)

Required Host port number.

int

channelName (common)

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

String

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.

Enum values:

  • 0

  • 1

  • 2

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

sessionHeadersEnabled (consumer)

Whether to include the server session headers in the Camel message when creating a Camel Message for incoming requests.

false

boolean

bridgeErrorHandler (consumer (advanced))

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. 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

exceptionHandler (consumer (advanced))

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 (advanced))

Sets the exchange pattern when the consumer creates an exchange.

Enum values:

  • InOnly

  • InOut

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

lazyStartProducer (producer (advanced))

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

Message Headers

The CometD component supports 2 message header(s), which is/are listed below:

Name Description Default Type

CometdClientId (common)

Constant: COMETD_CLIENT_ID_HEADER_NAME

The clientId of the session.

String

subscription (common)

Constant: COMETD_SUBSCRIPTION_HEADER_NAME

The subscription.

String

Examples

Below, you can find some examples of 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, for example, the web resources are packaged inside the webapp folder -→ cometd://localhost:8080?resourceBase=classpath:webapp

Authentication

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

Setting up SSL for Cometd Component

Using the JSSE Configuration Utility

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.x

  • Java

  • Spring XML

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);
  <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"/>...

Spring Boot Auto-Configuration

When using cometd with Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

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

The component supports 11 options, which are listed below.

Name Description Default Type

camel.component.cometd.autowired-enabled

Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc.

true

Boolean

camel.component.cometd.bridge-error-handler

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. 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

camel.component.cometd.enabled

Whether to enable auto configuration of the cometd component. This is enabled by default.

Boolean

camel.component.cometd.extensions

To use a list of custom BayeuxServer.Extension that allows modifying incoming and outgoing requests.

List

camel.component.cometd.lazy-start-producer

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

Boolean

camel.component.cometd.security-policy

To use a custom configured SecurityPolicy to control authorization. The option is a org.cometd.bayeux.server.SecurityPolicy type.

SecurityPolicy

camel.component.cometd.ssl-context-parameters

To configure security using SSLContextParameters. The option is a org.apache.camel.support.jsse.SSLContextParameters type.

SSLContextParameters

camel.component.cometd.ssl-key-password

The password for the keystore when using SSL.

String

camel.component.cometd.ssl-keystore

The path to the keystore.

String

camel.component.cometd.ssl-password

The password when using SSL.

String

camel.component.cometd.use-global-ssl-context-parameters

Enable usage of global SSL context parameters.

false

Boolean
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