Presents your  
JAVA E-NEWSLETTER for August 28, 2003 
 
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JMS ALLOWS JAVA APPs TO COMMUNICATE WITH EACH OTHER   
  
For years, developers have been pondering how separate applications can 
communicate with each other. If the applications in question are Java 
programs, then the answer is Sun's Java Message Service (JMS), which was
integrated into the release of J2EE 1.3.   
  
JMS is Sun's take on Message-Oriented Middleware (MOM), which allows two
or more applications to communicate in a well-defined manner without 
knowing about the underlying communication implementation details.   
  
JMS is an API that requires an implementation. In order to use JMS in 
your applications, you'll need a JMS server and JMS client libraries for
that server. J2EE 1.3 comes with both pieces, so if you want to start right 
away, you can read Sun's JMS tutorial using the J2EE's built-in JMS 
functionality. There are also third-party JMS applications available. Some of 
the apps deliver superior speed, while others deliver reliability; 
however, all of these applications promise to offer both.   
http://java.sun.com/products/jms/tutorial/index.html   
  
Using JMS, there are two ways for applications to communicate with each 
other: Topics and Queues. Topics are used when a message needs to deliver 
to one or more consumers. (All subscribers to the Topic receive each 
message.) Topic publishing is known as Publish/Subscribe or Pub/Sub.   
  
Queues are used when only one subscriber needs to consume each message. 
This type of publishing is known as point-to-point (PTP). In PTP 
publishing, no matter how many processes subscribe to a Queue, only one
will receive a given message.   
  
If you have multiple applications that must communicate with each 
other--especially those running in separate virtual machines--then JMS
might be for you. Learn more by visiting Sun's JMS page.   
http://java.sun.com/products/jms/   
  
David Petersheim is a Senior Java Developer with Genscape, Inc. He 
designs and develops server-side applications to acquire and process
real-time energy data.   
  
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