Summary

In this chapter we covered the fundamentals of JMS. First of all we looked at the JMS architecture. We defined JMS providers as software vendors who implement the interfaces defined in the JMS specification and JMS clients as Java language applications that exchange JMS messages using the services provided by the JMS provider.

Note that portable JMS clients should use only the standard JMS interfaces in application code and should not use any of the provider-specific implementation classes. Throughout the chapter we used standard JMS interfaces, and demonstrated them with a few basic examples.

Next we considered the two types of Administered objects. These are pre-configured objects stored in a namespace by JMS administrators for the use of JMS clients. Connection factories are Administered objects used by JMS clients for creating connections to a JMS provider. Destination objects are used by JMS clients to specify the locations to and from which they send and receive messages. The two types of destination, queue and topic, were described in detail.

We also looked at the two message models employed by JMS. Point-to-Point messaging invokes the notion of a queue, where the First-In, First-Out rule is applied. In Publish/Subscribe messaging topics are used. When a message is published on a topic, it is sent to every subscriber of that topic.

The final example in the chapter demonstrated the use of message producers, message consumers, and message clients. A simple chat application was set up, and messages were sent between two users running separate JMS clients.

Although JMS messages were covered briefly, we will consider them in greater detail in the next chapter.