厚積而薄發

與Queue不同的是，Topic實現的是發布/訂閱模型，在下面的例子中，啟動2個消費者共同監聽一個Topic，然后循環給這個Topic中發送多個消息。

import javax.jms.Connection;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageConsumer;
import javax.jms.MessageListener;
import javax.jms.MessageProducer;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.jms.Topic;

import org.apache.activemq.ActiveMQConnectionFactory;
import org.apache.activemq.command.ActiveMQTopic;


public class TopicTest {

    public static void main(String[] args) throws Exception {
        ActiveMQConnectionFactory factory = new ActiveMQConnectionFactory("vm://localhost");
   
        Connection connection = factory.createConnection();
        connection.start();
       
        //創建一個Topic
        Topic topic= new ActiveMQTopic("testTopic");
        Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
        
        //注冊消費者1
        MessageConsumer comsumer1 = session.createConsumer(topic);
        comsumer1.setMessageListener(new MessageListener(){
            public void onMessage(Message m) {
                try {
                    System.out.println("Consumer1 get " + ((TextMessage)m).getText());
                } catch (JMSException e) {
                    e.printStackTrace();
                }
            }
        });
       
        //注冊消費者2
        MessageConsumer comsumer2 = session.createConsumer(topic);
        comsumer2.setMessageListener(new MessageListener(){
            public void onMessage(Message m) {
                try {
                    System.out.println("Consumer2 get " + ((TextMessage)m).getText());
                } catch (JMSException e) {
                    e.printStackTrace();
                }
            }
           
        });
       
        //創建一個生產者，然后發送多個消息。
        MessageProducer producer = session.createProducer(topic);
        for(int i=0; i<10; i++){
            producer.send(session.createTextMessage("Message:" + i));
        }
    }

}

運行后得到下面的輸出結果：

Consumer1 get Message:0
Consumer2 get Message:0
Consumer1 get Message:1
Consumer2 get Message:1
Consumer1 get Message:2
Consumer2 get Message:2
Consumer1 get Message:3
Consumer2 get Message:3
Consumer1 get Message:4
Consumer2 get Message:4
Consumer1 get Message:5
Consumer2 get Message:5
Consumer1 get Message:6
Consumer2 get Message:6
Consumer1 get Message:7
Consumer2 get Message:7
Consumer1 get Message:8
Consumer2 get Message:8
Consumer1 get Message:9
Consumer2 get Message:9

說明每一個消息都會被所有的消費者消費。