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.

Sendings 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 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.

You can also use the @Property and @Header annotations on method parameters to tell Camel which method parameters bind to some header/property value and which parameter binds to the message body. You can use @Body to be precise about which parameter is the 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.

You could process some headers if you wish like this

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 (again with possible type conversion too).

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");
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