Patterns: Broker Interactions for Intra- and Inter-enterprise

138 Broker Interactions for Intra- and Inter-enterprise

7.5 Java Message Service (JMS)

Messaging middleware is a popular choice for accessing existing enterprise

systems in an asynchronous manner. A standard way of using messaging

middleware from a Java application is using the Java Message Service (JMS)

interface. JMS offers Java programmers a common way to create, send, receive

and read enterprise messages. The JMS specification was developed by Sun

Microsystems with the active involvement of IBM, other enterprise messaging

vendors, transaction processing vendors, and RDBMS vendors.

In IBM WebSphere Application Server V5.0, the J2EE 1.3 specification is

implemented, which includes JMS 1.0 and EJB 2.0.

According to the JMS 1.0 specification, a message provider is integrated in an

application server. As shown in Figure 7-2, the integrated message provider

makes it possible to communicate asynchronously with other WebSphere

applications, without installing separate messaging software like IBM

WebSphere MQ. WebSphere’s integrated JMS server is based on IBM

WebSphere MQ.

Figure 7-2 Integrated JMS Provider

J2EE ServerJ2EE Server

Message

PUT

Message

GET

J2EE Application

Web

Message

GET

Message

PUT

J2EE Application

Web

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.