Java Message Service

Chapter 4. Publish-and-Subscribe Messaging

This chapter focuses on the publish-and-subscribe (pub/sub) messaging model that was introduced in Chapter 2. The pub/sub messaging model allows a message producer (also called a publisher) to broadcast a message to one or more consumers (called subscribers). There are three important aspects of the pub/sub model:

• Messages are pushed to consumers, which means that consumers are delivered messages without having to request them. Messages are exchanged through a virtual channel called a topic. A topic is a destination where producers can publish, and subscribers can consume, messages. Messages delivered to a topic are automatically pushed to all qualified consumers.

• As in enterprise messaging in general, there is no coupling of the producers to the consumers. Subscribers and publishers can be added dynamically at runtime, which allows the system to grow or shrink in complexity over time.

• Every client that subscribes to a topic receives its own copy of messages published to that topic. A single message produced by one publisher may be copied and distributed to hundreds, or even thousands of subscribers.

In Chapter 2 you learned the basics of the pub/sub model by developing a simple chat client. In this chapter we will build on those lessons and examine more advanced features of this model, including guaranteed messaging, topic-based addressing, durable subscriptions, request-reply, and temporary topics.

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