ejb3: message drive bean(MDB)示例

上一篇已经知道了JMS的基本操作，今天来看一下ejb3中的一种重要bean：Message Drive Bean(mdb)

如果要不断监听一个队列中的消息,通常我们需要写一个监听程序,这需要一定的开发量,而且如果要实现高并发处理,也不易扩展,而MDB则自动实现了该功能,简单点讲,MDB的应用部署到jboss后,能自动监听目标队列,一旦有消息接收,会触发onMessage事件,开发人员可以在该事件处理中扩展自己的业务逻辑.

一、定义一个MDB

 package mdb;

 import javax.ejb.ActivationConfigProperty;
 import javax.ejb.MessageDriven;
 import javax.jms.JMSException;
 import javax.jms.Message;
 import javax.jms.MessageListener;
 import javax.jms.TextMessage;

 import util.LoggerUtil;

 @MessageDriven(name = "HelloWorldQueueMDB", activationConfig = {
         @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue"),
         @ActivationConfigProperty(propertyName = "destination", propertyValue = "jms/queue/mytest"),
         @ActivationConfigProperty(propertyName = "acknowledgeMode", propertyValue = "Auto-acknowledge") })
 public class HelloWorldMDB implements MessageListener {

     @Override
     public void onMessage(Message msg) {
         TextMessage txtMsg = null;
         try {
             if (msg instanceof TextMessage) {
                 txtMsg = (TextMessage) msg;
                 String msgContent = txtMsg.getText();
                 LoggerUtil.info("Received Message from queue: " + msgContent);
             } else {
                 LoggerUtil.warning("Message of wrong type: "
                         + txtMsg.getClass().getName());
             }
         } catch (JMSException e) {
             throw new RuntimeException(e);
         }

     }

 }

HelloWorldMDB

注意该类上的注解,它表明了要监听哪个Queue(可以参考上一篇的内容,先在jboss中建好该queue),其它没什么特别的,把它放一个dynamic web中,打成war包部署到jboss上,为演示效果,部署后,先不启动该应用

附:pom.xml文件的内容

 <?xml version="1.0" encoding="UTF-8"?>

 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
     <modelVersion>4.0.0</modelVersion>

     <groupId>cnblogs</groupId>
     <artifactId>helloworld-mdb</artifactId>
     <version>0.0.1-SNAPSHOT</version>
     <packaging>war</packaging>
     <name>helloworld-mdb</name>

     <dependencyManagement>
         <dependencies>
             <dependency>
                 <groupId>org.jboss.bom</groupId>
                 <artifactId>jboss-javaee-6.0-with-tools</artifactId>
                 <version>1.0.7.Final</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
         </dependencies>
     </dependencyManagement>

     <dependencies>
         <dependency>
             <groupId>org.jboss.spec.javax.jms</groupId>
             <artifactId>jboss-jms-api_1.1_spec</artifactId>
             <scope>provided</scope>
         </dependency>
         <dependency>
             <groupId>org.jboss.spec.javax.ejb</groupId>
             <artifactId>jboss-ejb-api_3.1_spec</artifactId>
             <scope>provided</scope>
         </dependency>
     </dependencies>

 </project>

pom.xml

二、测试验证

a) 可以参考上一篇JMS的内容,另建一个常规的project,向该队列发送消息(注意:仅发送,不要接收,否则消息被收走了,MDB就收不到消息了)

 package jms;

 import java.util.Hashtable;

 import javax.jms.Connection;
 import javax.jms.ConnectionFactory;
 import javax.jms.Destination;
 import javax.jms.JMSException;
 import javax.jms.MessageConsumer;
 import javax.jms.MessageProducer;
 import javax.jms.Session;
 import javax.jms.TextMessage;
 import javax.naming.Context;
 import javax.naming.InitialContext;
 import javax.naming.NamingException;

 public class App {

     public static void main(String[] args) throws NamingException, JMSException {

         final String lOOKUP_CONNECTION_FACTORY_NAME = "lookup.connectionfactory.name";
         final String lOOKUP_DESTINATION_NAME = "lookup.destination.name";

         ConnectionFactory connectionFactory = null;
         Connection connection = null;
         Session session = null;
         MessageProducer producer = null;
         MessageConsumer consumer = null;
         Destination destination = null;
         TextMessage message = null;
         Context context = null;

         try {
             // 创建上下文（默认会从应用的classpath下加载jndi.properties做为环境参数）
             context = new InitialContext();

             // 把环境参数取出来，后面会用到
             Hashtable<String, String> env = (Hashtable<String, String>) context
                     .getEnvironment();

             // 查找连接工厂
             connectionFactory = (ConnectionFactory) context.lookup(env
                     .get(lOOKUP_CONNECTION_FACTORY_NAME));

             // 查找目标队列
             destination = (Destination) context.lookup(env
                     .get(lOOKUP_DESTINATION_NAME));

             // 创建连接
             connection = connectionFactory.createConnection(
                     env.get(Context.SECURITY_PRINCIPAL),
                     env.get(Context.SECURITY_CREDENTIALS));

             // 创建会话
             session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);

             // 创建生产者(即发送者)
             producer = session.createProducer(destination);

             // 创建消费者(即接收者)
             consumer = session.createConsumer(destination);

             // 开始连接
             connection.start();

             // 发送消息

             message = session.createTextMessage("HELLO,I AM GLAD TO SEE YOU!");

             producer.send(message);

             System.out.println("发送成功!");

         } catch (NamingException e) {
             e.printStackTrace();
         } catch (JMSException e) {
             e.printStackTrace();
         } finally {
             // 释放资源
             if (context != null) {
                 context.close();
             }

             if (connection != null) {
                 connection.close();
             }

         }
     }

 }

Send Message

b) 然后在jboss中,再把该应用启用起来,观察console窗口的输出:

三、xml方式配置MDB

刚才我们是用注解方式来配置MDB的，这种方式不需要xml配置文件，十分方便，但是也有缺点，配置与代码紧耦合，如果以后要修改queue名称，就得改代码，重新编译，所以jboss也提供了xml配置方式

方法：在META-INF(非web项目)或WEB-INF(web项目)放置一个名为jboss-ejb3.xml(这是固定名称，不要修改!)

内容参考下面这样：

 <?xml version="1.0" encoding="UTF-8"?>
 <jboss:ejb-jar xmlns:jboss="http://www.jboss.com/xml/ns/javaee"
     xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:c="urn:clustering:1.0"
     xsi:schemaLocation="http://www.jboss.com/xml/ns/javaee http://www.jboss.org/j2ee/schema/jboss-ejb3-2_0.xsd http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/ejb-jar_3_1.xsd"
     version="3.1" impl-version="2.0">
     <enterprise-beans>
         <message-driven>
             <ejb-name>HelloWorldQueueMDB</ejb-name>
             <ejb-class>mdb.HelloWorldMDB</ejb-class>
             <activation-config>
                 <activation-config-property>
                     <activation-config-property-name>destinationType</activation-config-property-name>
                     <activation-config-property-value>javax.jms.Queue</activation-config-property-value>
                 </activation-config-property>
                 <activation-config-property>
                     <activation-config-property-name>destination</activation-config-property-name>
                     <activation-config-property-value>jms/queue/mytest</activation-config-property-value>
                 </activation-config-property>
                 <activation-config-property>
                     <activation-config-property-name>acknowledgeMode</activation-config-property-name>
                     <activation-config-property-value>Auto-acknowledge</activation-config-property-value>
                 </activation-config-property>
             </activation-config>
         </message-driven>
     </enterprise-beans>
     <assembly-descriptor>
         <c:clustering>
             <ejb-name>DDBasedClusteredSFSB</ejb-name>
             <c:clustered>true</c:clustered>
         </c:clustering>
     </assembly-descriptor>
 </jboss:ejb-jar>

jboss-ejb3.xml

然后把HelloWorldQueueMDB类上的那一堆注解全注释掉，再跑下，顺利的话，也同样可以接收消息

示例源代码下载:mdb-sample.zip