J2EE Design Patterns

Name

Event-Driven Consumer Pattern

Goal

To deliver messages to a client as quickly as possible, while minimizing the complexity of the code, the developer must assemble to handle messages.

Participants

Message server

Receives incoming messages.

Application server

Communicates with the message server and retrieves new messages.

Client code

Performs the actual processing, based on calls from the application server.

Interactions

Incoming messages are delivered to the message server. The application server communicates with the message server and retrieves new messages destined for a particular client. When new messages arrive, the application server calls appropriate client code to process them.

Notes

Message-driven EJBs implement the Event-Driven Consumer pattern. JMS also supports implementing event-driven consumers directly. JavaMail supports event-driven consumers via the FolderListener interface, although we do not recommend it. Most event-driven consumer implementations simply push implementation to the application server/application framework level, while still implementing a polling consumer behind the scenes.