EJB 2.0之MDB 示例教程

MDB就是异步消息的消费者。当消息到达之后，由容器负责调用MDB。客户端发送消息到destination，MDB作为一个MessageListener接受消息。用程序员去关心MessageBean的管理。

MDB只是作为服务器端接收消息，而且ConnectionFacotory和JNDI都要自己去服务器上配置。

 

1、Weblogic配置JMS服务

具体JMS在weblogic服务器配置请看：http://qidaoxp.iteye.com/admin/blogs/480058

2、Example Bean

import javax.ejb.MessageDrivenBean;
import javax.ejb.MessageDrivenContext;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.jms.TextMessage;

/**
 * Demonstrates usage of a Message-Driven EJB.
 *
 * @author Copyright (c) 1999-2008 by BEA Systems, Inc. All Rights Reserved.
*/
public class MessageTraderBean implements MessageDrivenBean, MessageListener {

  private static final boolean VERBOSE = true;
  private MessageDrivenContext m_context;
  private int m_tradeLimit;

  /**
   * Sets the session context.
   *
   * @param ctx               MessageDrivenContext Context for session
   */
  public void setMessageDrivenContext(MessageDrivenContext ctx) {
    m_context = ctx;
  }

  /**
   * Retrieve the int value of the TextMessage and
   * increment the RMI counter by that much.
   */
  public void onMessage(Message msg) {
    TextMessage tm = (TextMessage) msg;
    try {
      String text = tm.getText();
      log("Received new quote : "+text);
    }
    catch(JMSException ex) {
      System.err.println("An exception occurred: "+ex.getMessage());
    }
  }

  /**
   * This method is required by the EJB Specification,
   * but is not used by this example.
   */
  public void ejbCreate() { }

  /**
   * This method is required by the EJB Specification,
   * but is not used by this example.
   */
  public void ejbRemove() { }

  static void p(String s) {
    System.out.println("*** <MessageTraderBean> "+s);
  }

  private void log(String s) {
    if (VERBOSE) System.out.println(s);
  }
}

 

3、ejb-jar.xml

<ejb-jar>
	<enterprise-beans>
		<message-driven>
			<display-name>MessageTraderBean</display-name>
			<ejb-name>MessageTraderBean</ejb-name>
			<ejb-class>ejb.mdb.MessageTraderBean</ejb-class>
			<transaction-type>Container</transaction-type>
			<message-destination-type>javax.jms.Topic</message-destination-type>
		</message-driven>
	</enterprise-beans>
	<assembly-descriptor>
		<container-transaction>
			<method>
				<ejb-name>MessageTraderBean</ejb-name>
				<method-name>*</method-name>
			</method>
			<trans-attribute>Required</trans-attribute>
		</container-transaction>
	</assembly-descriptor>
</ejb-jar>

 

4、weblogic-ejb-jar.xml

<weblogic-ejb-jar>
<weblogic-enterprise-bean>
		<ejb-name>MessageTraderBean</ejb-name>
		<message-driven-descriptor>
			<destination-jndi-name>testtopic</destination-jndi-name>
		</message-driven-descriptor>
	</weblogic-enterprise-bean>
</weblogic-ejb-jar>

 

注意destination-jndi-name为自己在服务器上配置的jndi要一致。