4.5. Summary

In this chapter, we covered basic messaging concepts, JMS, and MDBs. Messaging is an extremely powerful technology for the enterprise, and it helps build loosely coupled systems. JMS allows you to use message-oriented middleware (MOM) from enterprise Java applications. Using the JMS API to build a message consumer application can be time consuming, and MDBs make using MOM in a standardized manner through Java EE extremely easy.

Note, however, that messaging and MDBs are not right for all circumstances and can be overused. One such case is using the request/reply model (discussed in the sidebar “The request-reply model”), which entails a lot of extra complexity compared to simple PTP or pub-sub messaging. If you find yourself using this model extensively and in ways very close to synchronous messaging, it might be worth thinking about switching to a synchronous technology such as RMI, SOAP, or remote session bean calls.