Enterprise JavaBeans, Fourth Edition

JMS-Based Message-Driven Beans

Message-driven beans (MDBs) are stateless, server-side, transaction-aware components for processing asynchronous messages delivered via the Java Message Service. While a message-driven bean is responsible for processing messages, its container manages the component’s environment, including transactions, security, resources, concurrency, and message acknowledgment. It’s particularly important to note that the container manages concurrency. The thread-safety provided by the container gives MDBs a significant advantage over traditional JMS clients, which must be custom-built to manage resources, transactions, and security in a multithreaded environment. An MDB can process hundreds of JMS messages concurrently because numerous instances of the MDB can execute concurrently in the container.

A message-driven bean is a complete enterprise bean, just like a session or entity bean, but there are some important differences. While a message-driven bean has a bean class and EJB deployment descriptor, it does not have EJB object or home interfaces. These interfaces are absent because the message-driven bean is not accessible via the Java RMI API; it responds only to asynchronous messages.

The ReservationProcessor EJB

The ReservationProcessor EJB is a message-driven bean that receives JMS messages notifying it of new reservations. The ReservationProcessor EJB is an automated version of the TravelAgent EJB that processes reservations sent via JMS. These messages ...