Service Activator – Core J2EE Patterns

The service activator design pattern is one of the Java EE patterns. It is an SI (spring integration) component. It is responsible for triggering or activating a service object or bean which is managed by the spring. A service activator searches through the message channel in order to look for messages. When the message arrives, it calls upon the processing method of the service bean, which is generally, just a POJO.

The processing method of the service passes the message or the payload of the message to the processing method, which is generally based upon the parameter type. In fact, it is not possible to pass the data to the processing method of the service. In this case, the service activator acts as an event style component which is responsible for triggering processing just in the instant when it receives the message.

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UML class Diagram for Service Activator

Let’s see the following UML class diagram for the Service Activator.

Service Activator

Despite that, the processing method usually requires the message data to perform work. You need certain components to implement the service activator design pattern. Each of these components has certain tasks to perform and certain problems to cater. These components include; client, request, service activator and business object. The client object needs an asynchronous processing facility from the business objects which are participating in a workflow.

The request object is a message object which is that client creates and sends to the service activator object. The service activator object is the main class of this design pattern. JMS specification has defined javax.jms.MessageListener interface, which implemented by the service activator object. You can also call the business object the target object. The client requires the access to this object, in an asynchronous mode. Either an entity bean or a session fulfill he role of the business object completely.