ejb3: message drive bean(MDB)示例

2023-08-12 20:30:04

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

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