Bean Integration

Camel supports the integration of beans with Camel message exchanges in a number of ways.

Bean Component

The Bean component supports the creation of a proxy via ProxyHelper to a Java interface; which the implementation just sends a message containing a BeanInvocation to some Camel endpoint.

Then there is a server side implementation which consumes a message and uses the Bean Binding to bind the message to invoke a method passing in its parameters.

Bean Post Processor

If a bean is defined in Spring XML and it has some Camel annotations then it can be processed to inject resources.

Sending messages

To allow sending of messages you can use @EndpointInject() annotation. This will inject either a ProducerTemplate or CamelTemplate so that the bean can send message exchanges.

e.g. lets send a message to the foo.bar queue in ActiveMQ at some point

public class Foo {
  @EndpointInject(uri="activemq:foo.bar")
  ProducerTemplate producer;

  public void doSomething() {
    if (whatever) {
      producer.sendBody("<hello>world!</hello>");
    }
  }
}

Consuming messages

To consume a message you use a @MessageDriven annotation to mark a particular method of a bean as being a consumer method. The uri of the annotation defines the Camel Endpoint to consume from. The Bean Binding is then used to convert the inbound Message to the parameter list used to invoke the method

e.g. lets invoke the onCheese() method with the String body of the inbound JMS message from ActiveMQ on the cheese queue; this will use the Type Converter to convert the JMS ObjectMessage or BytesMessage to a String - or just use a TextMessage from JMS

public class Foo {

  @MessageDriven(uri="activemq:cheese")
  public void onCheese(String name) {
    ...
  }
}

Spring Remoting

We support a Spring Remoting provider which uses Camel as the underlying transport mechanism. The nice thing about this approach is we can use any of the Camel transport Components to communicate between beans. It also means we can use Content Based Router and the other Enterprise Integration Patterns in between the beans; in particular we can use Message Translator to be able to convert what the on-the-wire messages look like in addition to adding various headers and so forth.

Bean binding

The binding of a Camel Message to a bean method call can occur in different ways

• if the bean can be converted to a Processor using the Type Converter mechanism then this is used to process the message. This mechanism is used by the ActiveMQ component to allow any MessageListener to be invoked by the Bean component
• if the body of the message can be converted to a BeanInvocation (the default payload used by the ProxyHelper) - then that its used to invoke the method and pass the arguments
• if the message contains the header org.apache.camel.MethodName then that method is invoked, converting the body to whatever the argument is to the method
• otherwise the type of the method body is used to try find a method which matches; an error is thrown if a single method cannot be chosen unambiguously.

By default the return value is set on the outbound message body.

For example you could write a method like this

public class Foo {

    @MessageDriven(uri = "activemq:my.queue")
    public void doSomething(String body) {
		// process the inbound message here
    }

}

Here Camel with subscribe to an ActiveMQ queue, then convert the message payload to a String (so dealing with TextMessage, ObjectMessage and BytesMessage in JMS), then process this method.

Using Annotations to bind parameters to the Exchange

You can also use the following annotations to bind parameters to different kinds of Expression

Annotation	Meaning
@Body	To bind to an inbound message body
@Header	To bind to an inbound message header
@Headers	To bind to the Map of the inbound message headers
@OutHeader	To bind to an outbound message header
@OutHeaders	To bind to the Map of the outbound message headers
@Property	To bind to a named property on the exchange
@Properties	To bind to the property map on the exchange

For example

public class Foo {
	
    @MessageDriven(uri = "activemq:my.queue")
    public void doSomething(@Header('JMSCorrelationID') String correlationID, @Body String body) {
		// process the inbound message here
    }

}

In the above you can now pass the Message.getJMSCorrelationID() as a parameter to the method (using the Type Converter to adapt the value to the type of the parameter).

Finally you don't need the @MessageDriven annotation; as the Camel route could describe which method to invoke.

e.g. a route could look like

from("activemq:someQueue").
  to("bean:myBean");

Here myBean would be looked up in the Registry (such as JNDI or the Spring ApplicationContext), then the body of the message would be used to try figure out what method to call.

If you want to be explicit you can use

from("activemq:someQueue").
  to("bean:myBean?methodName=doSomething");

Using Expression Languages

You can also use any of the Languages supported in Camel to bind expressions to method parameters when using bean integration. For example you can use any of these annotations...

Annotation	Description
@BeanShell	Inject a BeanShell expression
@EL	Inject an EL expression
@Groovy	Inject a Groovy expression
@JavaScript	Inject a JavaScript expression
@OGNL	Inject an OGNL expression
@PHP	Inject a PHP expression
@Python	Inject a Python expression
@Ruby	Inject a Ruby expression
@Simple	Inject an Simple expression
@XPath	Inject an XPath expression
@XQuery	Inject an XQuery expression

For example

public class Foo {
	
    @MessageDriven(uri = "activemq:my.queue")
    public void doSomething(@Path("/foo/bar/text()") String correlationID, @Body String body) {
		// process the inbound message here
    }
}