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Add the power of asynchronous processing to your JSPs

Create custom JSP tags to use with JMS

By Tarak Modi, JavaWorld.com, 02/09/01

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So, what does JMS have to do with MOM? JMS provides a standard Java-based interface to MOM's message services. My simplified definition of JMS is as follows: JMS is an API used to access MOM facilities from a Java application.

Figure 1 shows the pictorial form of the above definition.

Figure 1. The JMS architecture



JMS supports two popular messaging styles: point-to-point messaging and publish-and-subscribe messaging.

Point-to-point messaging

In point-to-point messaging, two applications use MOM to communicate with each other, often as an asynchronous replacement for RPC. As shown in Figure 2, JMS allows multiple senders, but only one receiver in this model. A queue, which channels the messages, forms the central concept of point-to-point messaging. An application interested in sending a message begins with a queue connection factory that obtains a queue connection. That queue connection then creates a queue session, the application's personal window into the connection. A JMS client uses that session to create a message producer, which sends messages to the queue.

On the other end, the receiving application goes through a similar sequence of obtaining a queue connection factory, a queue connection, and a queue session. The receiving application's functions differ from the sending application in that it uses the session to create a message consumer to receive messages from the queue.

Figure 2. Point-to-point messaging in JMS



Publish-and-subscribe messaging

When multiple applications need to receive the same message(s), they use the publish-and-subscribe model. Figure 3 illustrates that model, where a many-to-many relationship exists between the message producers and the message consumers. Note, as Figure 3 illustrates, that a topic forms the central concept in that model. Instead of message senders and receivers, you have message publishers and subscribers.

Figure 3. Publish-and-subscribe messaging in JMS



A publisher uses a topic connection factory to create a topic connection. It then uses that topic connection to create a topic session, which provides the publisher with a personal window into the topic connection. The publisher can now use the topic session to create a message producer, which publishes messages to the topic.

On the other end, the subscribing application goes through a similar sequence of obtaining a topic connection factory, a topic connection, and a topic session. The subscribing application differs from the publisher in that it uses the session to create a message consumer that subscribes to messages from the topic.

Although I've glossed over a number of issues regarding JMS usage, what I've included above is all you need to know about JMS to create the custom JSP tags discussed in this article.

The JSP custom tag architecture

Many developers have written articles on creating and using custom tags, so I won't spend much time introducing the basics of JSP custom tags. In addition, Sun provides a sample chapter on creating custom JSP tags from the book Core Servlets and JavaServer Pages, by Marty Hall. See the Resources below for references to this and other sources that cover creating custom JSP tags.

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