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| <task id="messbwiz" xml:lang="en-us"> |
| <title>Creating Message-driven Beans</title> |
| <shortdesc>You can use a wizard to create a message-driven bean and add it |
| to your project.</shortdesc> |
| <prolog><metadata> |
| <keywords><indexterm>message-driven beans<indexterm>creating</indexterm></indexterm> |
| </keywords> |
| </metadata></prolog> |
| <taskbody> |
| <context><p>The message-driven bean wizard helps you create an Enterprise |
| message-driven bean by walking you through the creation process and by providing |
| you with output files that you can use or that you can modify for use with |
| your application.</p> <p>To create a message-driven bean, complete the following |
| steps:</p></context> |
| <steps> |
| <step><cmd>From the <tm tmclass="special" tmowner="Sun Microsystems, Inc." |
| tmtype="tm" trademark="Java">Java</tm> EE perspective, expand your EJB project |
| in the Project Explorer view.</cmd></step> |
| <step><cmd>Right click on the <b>Message-Driven Bean</b> icon, and select <menucascade> |
| <uicontrol>New</uicontrol><uicontrol>Message-Driven Bean</uicontrol></menucascade> from |
| the pop-up menu.</cmd><stepresult> The <uicontrol>Create Message-Driven Bean</uicontrol> wizard |
| appears.</stepresult></step> |
| <step><cmd>Follow the project wizard prompts.</cmd></step> |
| </steps> |
| <postreq><p><b>General Information</b></p><dl><dlentry> |
| <dt><b>Destination name</b></dt> |
| <dd>This field provides the attribute <b>mappedName</b> to the <b>@MessageDriven</b> annotation. |
| This attribute specifies the product-specific name to which the message-driven |
| bean should be mapped. You can also use this attribute to specify the JNDI |
| name of the destination from which the bean will consume messages.</dd> |
| </dlentry></dl> <dl><dlentry> |
| <dt><b>Destination type</b></dt> |
| <dd>To send a JMS message, we need a connection to the JMS provider and a |
| destination address for the message. A JMS connection factory makes the connection |
| to the provider possible. In JMS, messages are not sent directly to applications; |
| they are sent to topics or queues:<dl><dlentry> |
| <dt>Queue:</dt> |
| <dd>Queue is used as a destination for pointtopoint messaging. The <b>point-to-point</b> |
| messaging model allows JMS clients to send and receive messages both synchronously |
| and asynchronously via virtual channels known as <i>queues</i>. The p2p messaging |
| model has traditionally been a pull- or polling-based model, where messages |
| are requested from the queue instead of being pushed to the client automatically. |
| A queue may have multiple receivers, but only one receiver may receive each |
| message. Messages holding this queue are of <b>MapMessages</b> type, which |
| stores the information about the email as name/value pair.</dd> |
| </dlentry><dlentry> |
| <dt>Topic:</dt> |
| <dd>Topic is used as a destination for publish/subscribe messaging. In <b>publish-and-subscribe</b> |
| messaging, one producer can send a message to many consumers through a virtual |
| channel called a <i>topic</i>. Consumers can choose to subscribe to a topic. |
| Any messages addressed to a topic are delivered to all the topic's consumers. |
| Every consumer receives a copy of each message. The pub/sub messaging model |
| is a push-based model, where messages are automatically broadcast to consumers |
| without them having to request or poll the topic for new messages. In the |
| pub/sub messaging model, the producer sending the message is not dependent |
| on the consumers receiving the message. Optionally, JMS clients that use pub/sub |
| can establish durable subscriptions that allow consumers to disconnect and |
| later reconnect and collect messages that were published while they were disconnected.</dd> |
| </dlentry></dl></dd> |
| </dlentry></dl> <dl><dlentry> |
| <dt><b>Transaction type</b></dt> |
| <dd>The <b>Transaction type</b> field is used to specify whether the transaction |
| is handled by the <b>Container</b> or the <b>Bean</b>.</dd> |
| </dlentry></dl> <dl><dlentry> |
| <dt><b>Interfaces</b></dt> |
| <dd>Message-driven beans usually implement the <b>javax.jms.MessageListener</b> |
| interface. A <i>MessageListener object</i> is used to receive asynchronously |
| delivered messages. This interface defines the <b>onMessage()</b> method. |
| This method processes the JMS messages received by a bean.</dd> |
| </dlentry></dl></postreq> |
| </taskbody> |
| </task> |
