We first described the Java Message Service (JMS) API. We described two messaging modes that JMS supports: point-to-point and publish/subscribe. In point-to-point mode a client, or message producer, sends a message to a queue. In publish/subscribe mode a message producer sends a message to a topic. A message recipient is referred to a message consumer. A queue or topic consumer can be either synchronous or asynchronous.

We looked at a number of examples of Java applications running outside an EJB container using JMS. We looked at queue and topic producers and both synchronous and asynchronous queue and topic consumers.

Message Driven Beans (MDBs) are provided where our messaging systems need the services offered by an EJB container. MDBs are EJB components which act as asynchronous message consumers. Although MDBs may implement non JMS messaging systems, all EJB compliant servers must support JMS-based MDBs.

MDBs can use point-to-point (queue) or publish/subscribe (topic) modes.

JMS...