Java Message Service API

The JMS API is a Message-Oriented Middleware (MOM) API. It was designed by a collaboration of several companies, including Sun Microsystems and IBM. Version 1 of the API was released in August 1998. The purpose of JMS is to enable applications to transmit and receive messages in an asynchronous and reliable way. The JMS API also defines interfaces to allow applications written using JMS to communicate with other messaging APIs.

The JMS designers' aims were as follows:

• To minimize the messaging concepts that a programmer needs to understand

• Provide communication that is loosely coupled, asynchronous, and reliable

• Have a consistent API that is independent of the JMS provider

• Maximize the portability of JMS applications

The JMS API provides messaging that is

• Loosely coupled— The sender and receiver may have no information about each other or the mechanisms used to process messages.

• Asynchronous— Receivers do not request messages. Messages can be delivered as they arrive. The sender does not wait for a reply.

• Reliable— A message is sent and received once and only once.

Note the JMS API does not specify how to control the privacy and integrity of messages. The type and level of message security is left to the JMS providers and is configured by administrators not by J2EE clients.

JMS and J2EE

From J2EE version 1.3 onward, the JMS API became an integral part of the J2EE requirements and J2EE containers must support both the point-to-point and publish/subscribe models. Support for JMS within the J2EE platform provides the following functionality and features:

• Message-Driven Beans for the sending and receiving of asynchronous messages (Message-Driven Beans are covered on Day 10)

• Support for distributed transactions

• Concurrent consumption of messages

An additional goal is to provide loosely coupled, reliable, asynchronous communication with legacy systems.

Programmatically, JMS can be considered a container-managed resource, similar to a JDBC connection. Application clients, EJBs, and Web components can all utilize the JMS API to send and receive messages. Note, however, that Applets are not required to support JMS.

The addition of the JMS API to J2EE simplifies enterprise software development and provides access to existing Enterprise Information Systems (EIS) and other legacy systems.