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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" |
| "concept.dtd"> |
| <concept id="messb" xml:lang="en-us"> |
| <title>Message-driven Beans</title> |
| <shortdesc></shortdesc> |
| <prolog><metadata> |
| <keywords><indexterm>message-driven beans<indexterm>overview</indexterm></indexterm> |
| </keywords> |
| </metadata></prolog> |
| <conbody> |
| <p>A <b>message-driven bean</b> is an enterprise bean that allows <tm tmclass="special" |
| tmowner="Sun Microsystems, Inc." tmtype="tm" trademark="Java">Java</tm> EE |
| applications to process messages asynchronously. It acts as a <tm tmclass="special" |
| tmowner="Sun Microsystems, Inc." tmtype="tm" trademark="Java">Java</tm> Message |
| Service (JMS) message listener, which is similar to an event listener except |
| that it receives messages instead of events. The messages may be sent by any <tm |
| tmclass="special" tmowner="Sun Microsystems, Inc." tmtype="tm" trademark="Java">Java</tm> EE |
| component - an application client, another enterprise bean, or a Web component |
| - or by a JMS application or system that does not use <tm tmclass="special" |
| tmowner="Sun Microsystems, Inc." tmtype="tm" trademark="Java">Java</tm> EE |
| technology.</p> |
| <p>In JMS, a message is a <tm tmclass="special" tmowner="Sun Microsystems, Inc." |
| tmtype="tm" trademark="Java">Java</tm> object with two parts: a <b>header</b> and |
| a <b>body</b>. The header is composed of delivery information and metadata. |
| The message body carries the application data, which can take several forms: |
| text, serializable objects, byte streams, etc. The JMS API defines several |
| message types (<b>TextMessage, MapMessage, ObjectMessage</b>, and others) |
| and provides methods for delivering messages to and receiving messages from |
| other applications.</p> |
| </conbody> |
| </concept> |
