JMS发布/订阅消息传送例子

Posted 2020-08-27 爷的眼睛闪亮

阅读目录

• 前言
• 在Tomcat中配置JNDI
• 在Web工厂中编写代码
• 参考资料

前言

基于上篇文章"基于Tomcat + JNDI + ActiveMQ实现JMS的点对点消息传送"很容易就可以编写一个发布/订阅消息传送例子，相关环境准备与该篇文章基本类似，主要的区别如下。

在Tomcat中配置JNDI

配置连接工厂和话题

    <Resource name="topic/connectionFactory" auth="Container"
        type="org.apache.activemq.ActiveMQConnectionFactory" description="JMS Connection Factory"
        factory="org.apache.activemq.jndi.JNDIReferenceFactory"
        brokerURL="failover:(tcp://localhost:61616)?initialReconnectDelay=100&amp;maxReconnectAttempts=5"
        brokerName="LocalActiveMQBroker" useEmbeddedBroker="false" />
        
    <Resource name="topic/topic0" 
        auth="Container"
        type="org.apache.activemq.command.ActiveMQTopic" description="My Topic" factory="org.apache.activemq.jndi.JNDIReferenceFactory"
        physicalName="TestTopic" />

在Web工厂中编写代码

新建一个发布者Servlet

package pubSub;

import java.io.IOException;
import java.io.PrintWriter;

import javax.naming.InitialContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.jms.Topic;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.jms.TopicPublisher;
import javax.jms.DeliveryMode;
import javax.jms.TopicSession;
import javax.jms.TopicConnection;
import javax.jms.TopicConnectionFactory;

/**
 * Servlet implementation class JMSTest
 */
@WebServlet("/Publish")
public class Publisher extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public Publisher() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();

        try {
            // get the initial context
            InitialContext ctx = new InitialContext();

            // lookup the topic object
            Topic topic = (Topic) ctx.lookup("java:comp/env/topic/topic0");

            // lookup the topic connection factory
            TopicConnectionFactory connFactory = (TopicConnectionFactory) ctx
                    .lookup("java:comp/env/topic/connectionFactory");

            // create a topic connection
            TopicConnection topicConn = connFactory.createTopicConnection();

            // create a topic session
            TopicSession topicSession = topicConn.createTopicSession(false,
                    Session.AUTO_ACKNOWLEDGE);

            // create a topic publisher
            TopicPublisher topicPublisher = topicSession.createPublisher(topic);
            topicPublisher.setDeliveryMode(DeliveryMode.NON_PERSISTENT);

            // create the "Hello World" message
            TextMessage message = topicSession.createTextMessage();
            message.setText("Hello World");

            // publish the messages
            topicPublisher.publish(message);

            // print what we did
            out.write("Message published: " + message.getText());

            // close the topic connection
            topicConn.close();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}

新建一个订阅者Servlet

package pubSub;

import java.io.IOException;
import java.io.PrintWriter;

import javax.jms.Session;
import javax.jms.TextMessage;
import javax.jms.Topic;
import javax.jms.TopicConnection;
import javax.jms.TopicConnectionFactory;
import javax.jms.TopicSession;
import javax.jms.TopicSubscriber;
import javax.naming.InitialContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Receive
 */
@WebServlet("/Subscribe")
public class Subscriber extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public Subscriber() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();

        try {
            // get the initial context
            InitialContext ctx = new InitialContext();

            // lookup the topic object
            Topic topic = (Topic) ctx.lookup("java:comp/env/topic/topic0");

            // lookup the topic connection factory
            TopicConnectionFactory connFactory = (TopicConnectionFactory) ctx
                    .lookup("java:comp/env/topic/connectionFactory");

            // create a topic connection
            TopicConnection topicConn = connFactory.createTopicConnection();

            // create a topic session
            TopicSession topicSession = topicConn.createTopicSession(false,
                    Session.AUTO_ACKNOWLEDGE);

            // create a topic subscriber
            TopicSubscriber topicSubscriber = topicSession
                    .createSubscriber(topic);

            // start the connection
            topicConn.start();

            // receive the message
            TextMessage message = (TextMessage) topicSubscriber.receive();

            // print the message
            out.write("Message received: " + message.getText());

            // close the topic connection
            topicConn.close();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}

运行Web工程，分别打开多个标签访问订阅servlet，然后访问发布servlet，结果如下：

在订阅者订阅消息的时候，一开始没接收到消息，一旦发布者发布消息后，订阅者马上收到消息。