Example of publishing/subscribing to messages through JMS and example of subscribing to messages through jms

Example of publishing/subscribing to messages through JMS and example of subscribing to messages through jms

Based on the previous article "Tomcat + JNDI + ActiveMQ to implement JMS point-to-point message transmission", you can easily compile a publish/subscribe message transmission example. The environment preparation is similar to this article, the main differences are as follows.

Configure JNDI in Tomcat

Configure the connection factory and topic

    <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" />

Compile code in the Web Factory

Create a publisher 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    }}

Create a subscriber 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    }}

Run the Web Project, open multiple tags to access the subscription servlet, and then access the published servlet. The result is as follows:

When a subscriber subscribes to a message, the subscriber does not receive the message at first. Once the subscriber publishes the message, the subscriber immediately receives the message.

 

Code reference: http://howtodoinjava.com/jms/jms-publish-subscribe-message-example/