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<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>