在上一篇介绍如何通过java往jms消息队列里面写消息和读取消息，本文介绍如何通过java往jms主题里写消息和读取消息。

消息发布

同样将消息发布到主题中，需要经过以下步骤

• 连接jms服务器
• 获取连接工厂(Connection Factory)
• 通过连接工厂创建主题连接（TopicConnection)
• 通过主题连接创建主题会话（TopicSession)
• 通过主题会话创建主题发布者（Publisher)
• 创建消息(Message)
• 通过发布者将消息发送到主题中

代码实现：

package asan.demo.jms;import java.util.Hashtable;
import javax.jms.JMSException;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.jms.Topic;
import javax.jms.TopicConnection;
import javax.jms.TopicConnectionFactory;
import javax.jms.TopicPublisher;
import javax.jms.TopicSession;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;public class JMSTopicSender {private TopicPublisher sender = null;private TopicSession session = null;private static final String JMS_FACTORY_JNDI = "jms/jms_test_connection_factory1";private static final String JMS_TOPIC_JNDI = "jms/jms_test_topic";public JMSTopicSender() {super();}public void sendMessage(String msg) {TextMessage textMsg;try {if (this.sender == null) {this.init();}textMsg = session.createTextMessage();textMsg.setText(msg);sender.send(textMsg);} catch (JMSException e) {e.printStackTrace();} catch (Exception ex) {ex.printStackTrace();}}//    1. 连接jms服务器//    2. 获取连接工厂(Connection Factory)//    3. 通过连接工厂创建主题连接（TopicConnection)//    4. 通过主题连接创建主题会话（TopicSession)//    5. 通过主题会话创建主题发布者（Publisher)//    6. 创建消息(Message)//    7. 通过发布者将消息发送到主题中private void init() throws NamingException, JMSException {Hashtable properties = new Hashtable();properties.put(Context.INITIAL_CONTEXT_FACTORY,"weblogic.jndi.WLInitialContextFactory");properties.put(Context.PROVIDER_URL, "t3://127.0.0.1:7101");properties.put(Context.SECURITY_PRINCIPAL, "weblogic");properties.put(Context.SECURITY_CREDENTIALS, "weblogic1");InitialContext ctx = new InitialContext(properties);TopicConnectionFactory jmsFactory =(TopicConnectionFactory)ctx.lookup(JMS_FACTORY_JNDI);TopicConnection jmsConn = jmsFactory.createTopicConnection();session = jmsConn.createTopicSession(false, Session.AUTO_ACKNOWLEDGE);Topic topic = (Topic)ctx.lookup(JMS_TOPIC_JNDI);sender = session.createPublisher(topic);}public static void main(String[]cmd){JMSTopicSender sender=new JMSTopicSender();sender.sendMessage("hello jms topic");}
}

与队列不同的是，此时主题没有订阅者，那么该消息就不存储在主题中，即使后面有订阅者订阅了该主题，也无法接收订阅前的消息。

消息订阅

从主题中订阅消息，需要经过以下步骤：

• 连接jms服务器
• 获取连接工厂(Connection Factory)
• 通过连接工厂创建主题连接（TopicConnection)
• 通过主题连接创建主题会话（TopicSession)
• 通过主题会话创建订阅者（Subscriber)
• 接收消息(Message)

代码实现：

package asan.demo.jms;import java.util.Hashtable;
import javax.jms.JMSException;
import javax.jms.Message;
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.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;public class JMSTopicReciver {private TopicSubscriber reciver = null;private static final String JMS_FACTORY_JNDI = "jms/jms_test_connection_factory1";private static final String JMS_TOPIC_JNDI = "jms/jms_test_topic";public JMSTopicReciver() {super();}public void reciveMessage() {try {if (this.reciver == null) {this.init();}System.out.println("waiting to recive message from jms topic "+JMS_TOPIC_JNDI);while(true){Message msg=reciver.receive();if(msg instanceof TextMessage){TextMessage textMsg=(TextMessage)msg;System.out.println("recive jms message:"+textMsg.getText());}}} catch (JMSException e) {e.printStackTrace();} catch (Exception ex) {ex.printStackTrace();}}//    1. 连接jms服务器//    2. 获取连接工厂(Connection Factory)//    3. 通过连接工厂创建主题连接（TopicConnection)//    4. 通过主题连接创建主题会话（TopicSession)//    5. 通过主题会话创建订阅者（Subscriber)//    6. 接收消息(Message)private void init() throws NamingException, JMSException {Hashtable properties = new Hashtable();properties.put(Context.INITIAL_CONTEXT_FACTORY,"weblogic.jndi.WLInitialContextFactory");properties.put(Context.PROVIDER_URL, "t3://127.0.0.1:7101");properties.put(Context.SECURITY_PRINCIPAL, "weblogic");properties.put(Context.SECURITY_CREDENTIALS, "weblogic1");InitialContext ctx = new InitialContext(properties);TopicConnectionFactory jmsFactory =(TopicConnectionFactory)ctx.lookup(JMS_FACTORY_JNDI);TopicConnection jmsConn = jmsFactory.createTopicConnection();TopicSession session = jmsConn.createTopicSession(false, Session.AUTO_ACKNOWLEDGE);Topic topic = (Topic)ctx.lookup(JMS_TOPIC_JNDI);reciver = session.createSubscriber(topic);jmsConn.start();}public static void main(String[]cmd){JMSTopicReciver consumer=new JMSTopicReciver();consumer.reciveMessage();}
}

运行代码，此时运行之前消息发布的代码，可以在控制台看到发送的消息

同样，稍微修改下上一篇文章的客户端程序，使整个过程看起来更清晰，修改后的客户端代码如下：

package asan.demo.jms;import java.util.Scanner;public class JMSClient {public JMSClient() {super();}public static void help() {System.out.println("Usage:java -jar JMSClient.jar sender/reciver/topicSender/topicReciver");System.out.println("sender:向jms队列发送消息");System.out.println("reciver:从队列中取出消息");System.out.println("topicSender:向jms主题发送消息");System.out.println("topicReciver:从主题中取出消息");}public static void main(String[] cmd) {if (cmd.length == 0) {help();return;}String mode = cmd[0];if ("sender".equalsIgnoreCase(mode)) {JMSSender sender = new JMSSender();Scanner sc = new Scanner(System.in);while (true) {System.out.println("input you message(input end to exist):");String msg = sc.nextLine();if ("end".equalsIgnoreCase(msg)) {return;}sender.sendMessage(msg);System.out.println("message send success");}} else if ("reciver".equalsIgnoreCase(mode)) {JMSReciver consumer = new JMSReciver();consumer.reciveMessage();} else if ("topicSender".equalsIgnoreCase(mode)) {JMSTopicSender sender = new JMSTopicSender();Scanner sc = new Scanner(System.in);while (true) {System.out.println("input you message(input end to exist):");String msg = sc.nextLine();if ("end".equalsIgnoreCase(msg)) {return;}sender.sendMessage(msg);System.out.println("message send success");}} else if ("topicReciver".equalsIgnoreCase(mode)) {JMSTopicReciver consumer = new JMSTopicReciver();consumer.reciveMessage();}}
}

打包运行，执行以下命令将客户端作为主题发布者

java -jar JMSDemo.jar topicSender

新建窗口，执行以下命令将客户端作为主题订阅者

java -jar JMSDemo.jar topicReciver

在发布者上发送消息，在订阅者上看到收到的消息

可以再多开一个窗口，再运行一个订阅者

登录weblogic控制台，进入domain->Services->Messaging->JMS Modules->jms_test_module->jms_test_topic可以查看当前主题订阅统计信息