Friday, June 25, 2010

Difference Between an Enterprise Application Client and an EJB


I want to build a J2EE JMS Application using Glassfish Application Server.
is it better to make an Application Client or a Message Driven Bean (MDB)  ?

Also, I would like to know the Difference between the two. 
Thanks !

Ans : 
An application client is a standalone JAVA program, which needs to have the main method. A message driven bean (MDB) is a JEE component that is managed by the JEE container. In order for an MDB to consume messages it needs to be deployed in a runing JEE container (in your case, Glassfish).

The advantage of an MDB is that the container manages transactions, security, resource, concurrency and message acknowledgement. When you write a standalone client you have to write custom code that deals with all this. Especially the concurrency part is very interesting. Using MDB's, the container can consume 100's of messages concurrently.

Since you will be using Glassfish anyway,  I do not see the advantage of having a standalone client to consume messages. I would go for MDB's.

MDB's are specially designed to consume JMS messages. However, JMS messages can easily be produced in any component (for example servlets, session beans, message driven beans, standalone clients...). For example, when a business method is invoked on a session bean, the business logic might decide to do a task asynchronously by sending a message to a destination using a connection to a JMS provider.


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