The Java EE 6 Tutorial

Publish/Subscribe Messaging Domain

In a publish/subscribe (pub/sub) product or application, clients address messages to a topic, which functions somewhat like a bulletin board. Publishers and subscribers are generally anonymous and can dynamically publish or subscribe to the content hierarchy. The system takes care of distributing the messages arriving from a topic’s multiple publishers to its multiple subscribers. Topics retain messages only as long as it takes to distribute them to current subscribers.

Pub/sub messaging has the following characteristics.

The JMS API relaxes this timing dependency to some extent by allowing subscribers to create durable subscriptions, which receive messages sent while the subscribers are not active. Durable subscriptions provide the flexibility and reliability of queues but still allow clients to send messages to many recipients. For more information about durable subscriptions, see Creating Durable Subscriptions.

Use pub/sub messaging when each message can be processed by zero, one, or many consumers. Figure 30–4 illustrates pub/sub messaging.

Figure 30–4 Publish/Subscribe Messaging

Diagram of pub/sub messaging, showing Client 1 publishing
a message to a topic, and the message being delivered to two subscribers to
the topic