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Java Message Service by Richard Monson-Haefel, David A Chappell

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Chapter 3. Anatomy of a JMS Message

This chapter focuses on the anatomy of a message: the individual parts that make up a message (headers, properties, and the different kinds of message payloads). Appendix B, Appendix C, and Appendix D cover additional information that will prove invaluable as a reference when developing JMS applications. Appendix B, provides in-depth information on the purpose and application of JMS headers; Appendix C, covers the rules governing the use of JMS properties; and Appendix D, covers the syntax of message selectors. Although you do not need to read these appendixes to understand subsequent chapters in this book, you will need them as a reference when implementing real JMS applications. After you finish reading this chapter, take a look at Appendixes Appendix B, Appendix C, and Appendix D so you're familiar with their content.

The Message is the most important part of the entire JMS specification. All data and events in a JMS application are communicated with messages, while the rest of JMS exists to facilitate the transfer of messages. They are the lifeblood of the system.

A JMS message both carries application data and provides event notification. Its role is unique to distributed computing. In RPC-based systems (CORBA, Java RMI, DCOM), a message is a command to execute a method or procedure, which blocks the sender until a reply has been received. A JMS message is not a command; it transfers data and tells the receiver that something has happened. ...

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