can any one please help me in understanding the differences between JMS and MDB
JMS is a specification. Message Driven Beans (MDB) is a type of EJB which are invoked based on JMS events. MDBs are used for asynchronous processing.
Ex: In JMS, you can have a "queue" to which messages can be delivered. This queue can be listened by a MDB. Whenever a message is delivered to the queue, the JMS server will invoke the onMessage method of the MDB and deliver it the message.