POJO Consuming

To consume a message you use the @Consume annotation to mark a particular method of a bean as being a consumer method. The value of the annotation defines the Camel Endpoint to consume from.

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

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

For example 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 {

  @Consume("activemq:cheese")
  public void onCheese(String name) {
    // do something here
  }
}

The Bean Binding is then used to convert the inbound Message to the parameter list used to invoke the method .

This basically creates a route that looks kinda like this:

from(uri).bean(theBean, "methodName");

Using a property to define the endpoint

The following annotations @Consume, @Produce, @EndpointInject, now offers a property attribute you can use to define the endpoint as a property on the bean. Then Camel will use the getter method to access the property.

For example:

public class MyService {
  private String serviceEndpoint;

  public void setServiceEndpoint(String uri) {
     this.serviceEndpoint = uri;
  }

  public String getServiceEndpoint() {
     return serviceEndpoint;
  }

  @Consume(property = "serviceEndpoint")
  public void onService(String input) {
     // do something
  }
}

The bean MyService has a property named serviceEndpoint which has getter/setter for the property. Now we want to use the bean for POJO Consuming, and hence why we use @Consume in the onService method. Notice how we use the property = "serviceEndpoint to configure the property that has the endpoint url.

If you define the bean in Spring XML, then you can configure the property as follows:

<bean id="myService" class="com.foo.MyService">
  <property name="serviceEndpoint" value="activemq:queue:foo"/>
</bean>

This allows you to configure the bean without with any dependency injection style.

Advanced use with property naming convention

Camel offers a naming convention which allows you to not have to explicit name the property. Camel uses this algorithm to find the getter method. The method must be a getXXX method.

  1. Use the property name if explicit given

  2. If no property name was configured, then use the method name

  3. Try to get the property with nameEndpoint (eg with Endpoint as postfix)

  4. Try to get the property with the name as is (eg no postfix or postfix)

  5. If the property name starts with on then omit that, and try step 3 and 4 again.

So in the example above, we could have defined the @Consume annotation as:

  @Consume(property = "service")
  public void onService(String input) {

Now the property is named "service" which then would match step 3 from the algorithm, and have Camel invoke the getServiceEndpoint method.

We could also have omitted the property attribute, to make it implicit

  @Consume
  public void onService(String input) {

Now Camel matches step 5, and loses the prefix on in the name, and looks for 'service' as the property. And because there is a getServiceEndpoint method, Camel will use this method.

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