Chapter 7. Technology options 139
An important new feature of EJB 2.0 is message-driven beans (MDB).
Message-driven beans are designed specifically to handle incoming JMS
messages. Further information on message-driven beans can be found in the
IBM Redbook EJB 2.0 Development with WebSphere Studio Application
Developer, SG24-6819.
7.5.1 What messaging is
Messaging is a form of communication between two or more software
applications or components. One strength of messaging is application
integration. Messaging communication is loosely coupled, as compared to tightly
coupled technologies such as Remote Method Invocation (RMI) or Remote
Procedure Calls (RPC). The sender does not need to know anything about the
receiver for communication. The message to be delivered is sent to a destination
(queue) by a sender component, and the recipient picks it up from there.
Moreover, the sender and receiver do not both have to be available at the same
time to communicate.
JMS has two messaging styles, or in other words, two domains:
? One-to-one, or point-to-point model
? Publish/subscribe model
7.5.2 JMS and IBM WebSphere MQ
When you want to integrate with an application not based on IBM WebSphere
Application Server V5.0, an external JMS Provider is needed. IBM WebSphere
MQ V5.3 includes built-in JMS Provider support with enhanced performance
features for integrating JMS applications with other applications.
WebSphere MQ enables application integration by allowing business
applications to exchange information across different platforms, sending and
receiving data as messages. WebSphere MQ takes care of network interfaces,
assures once and once only delivery of messages, deals with communications
protocols, dynamically distributes workload across available resources, and
handles recovery after system problems.
7.5.3 Advantages of JMS
The JMS standard is important because:
? It is the first enterprise messaging API that has achieved wide cross-industry
support.
? It simplifies the development of enterprise applications by providing standard
messaging concepts and conventions that apply across a wide range of
enterprise messaging systems.