Java Application & Application Servers

  I am in the process of developing/setting up an application server(Apache Tomcat and an RDBMS) and add the necessary functionalities to provide some kind of a publish-subscribe mechanism.  

I would like to be able to develop a Java-based GUI that allows the user to use to connect to the app server to subscribe for a certain type of data.  When that requested data is available it will be pushed to the subscriber.  

One way I can think of is as part of subscription, the subscriber will provide enough info (hostname, port number, etc...) so that the server will know who and where to 'push' the data to.  But that requires the subscriber (java app) to go into a continuous loop to listen for incoming data.  Is there a better and more graceful way of accomplishing this without using the polling mechism?

Any pointer is greatly appreciated.

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You have to use Java Messaging Service for these requirements (JMS)
Cloud Class® Course: Python 3 Fundamentals

This course will teach participants about installing and configuring Python, syntax, importing, statements, types, strings, booleans, files, lists, tuples, comprehensions, functions, and classes.

Go through Publish/Subscribe Messaging Domain descriptions in the above tutorial.
Hi Naeemg ,
              I also personally prefer EJB's as suggested by  Naeemg ..
                                                                         - Thanks

so , whats the problem then, just prize me . ........... ;););)
i think this is another suggestion for u. ;););)
johnchan2000Author Commented:
JMS was considered early on, being asynchronous an all that.  However, I decided to go with an app server (servlets and such) due to the firewall issues.

 Naeemq - thanks for the links, I will certainly look it up.

BTW., I was told that that Sun's JAXM package does provide some libraries that provide some kind of event listener that can be used with a java app (basically, instead of writing the code to continuously polling for incoming data, this package would take care of that).  Have anyone ever heard of such thing?

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