Sams Teach Yourself BEA WebLogic Server 7.0 in 21 Days

MOM is a very successful concept, except for the need to lock in to a single vendor. There is no standardization of MOM applications, which results in software being distinctly different in implementation and programming interface from vendor to vendor. Hence, the applications using MOM are not portable. The J2EE specification defines a standard mechanism to enable Java applications to access messaging systems of different providers in a consistent way. This mechanism is the Java Message Service API.

The JMS API is a common set of Java interfaces designed by Sun Microsystems and other partners to enable the creation and transportation of messages across different software components. This specification, a compliance requirement for all J2EE certification seeking packages, is a set of programming interfaces supporting point-to-point (or peer-to-peer) and publisher-subscriber messaging.

The JMS API ensures reliable asynchronous messaging:

• Asynchronous messaging The queue client awaiting a message does not need to look for new messages from time to time. Instead, the queue can deliver the message to the client when it arrives in the queue.

• Reliable messaging Once a message has been put into a queue, the message is positively delivered once, and only once, to the receiving component.

Any J2EE-compliant application server should incorporate these basic functions of JMS.