POJO producing

There are two different ways to send messages to any Camel Endpoint from a POJO:

  • Using @Produce or @EndpointInject

  • Or to hide using an interface

The following steps use the ActiveMQ component which is not yet supported on Camel 4.

Using @Produce

To allow sending of messages from POJOs you can use the @Produce annotation. This will inject a org.apache.camel.ProducerTemplate so that the bean can send messages.

The @Produce POJO annotations are not part of any Camel routes, and you cannot use errorHandler or onException with that.

For example to send a message to the foo queue on ActiveMQ:

public class Foo {
  @Produce("activemq:foo")
  ProducerTemplate producer;

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

The downside of this is that your code is now dependent on a Camel API, the ProducerTemplate. The next section describes how to remove this dependency.

See POJO Consuming for how to use a property on the bean as endpoint configuration, e.g., using the property attribute on @Produce or @EndpointInject.

Hiding the Camel APIs From Your Code

You can hide Camel APIs from your application code. You can add the @Produce annotation to an injection point (a field or property setter) using some interface you use in your business logic. Example:

public interface MyListener {
    // this method is request/reply (InOut) because the method has a return value
    // to use one way (InOnly) then the method should be a void method
    String sayHello(String name);
}

public class MyBean {
    @Produce("activemq:foo")
    protected MyListener producer;

    public void doSomething() {
        // lets send a message and get a response back
        String response = producer.sayHello("James");
    }
}

Here Camel will automatically inject a smart client side proxy at the @Produce annotation - an instance of the MyListener interface.

When we invoke methods on this interface the method call is turned into an object and is sent to the endpoint; in this case the ActiveMQ endpoint to queue foo. Because the sayHello method has a return type (String) then Camel will use Request Reply (InOut) messaging.

public interface MyListener {
    void sayHello(String name);
}

If the method is a void method, then Camel will use Event Message (InOnly) messaging.

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