Message-driven beans are similar to stateless session beans in that they have no conversational state and can process messages from more than one client at a time. Unlike a stateless session bean, a message-driven bean has no interfaces, just a bean class; clients do not access them through interfaces.
Message-driven beans (MDB) behave as listeners, executing a block of application code when a message arrives at a particular destination. To make MDBs really useful you need to utilize EJB references.
Developing Enterprise JavaBeans
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