ActiveMQ集群下的消息回流功能

------------------------------------------------------------------

"丢失"的消息

　　如果有broker1和broker2通过networkConnector连接，有一个consumer1连接到broker1,一个consumer2连接到broker2，程序往broker1上面发送30条消息，这时consumer2连接到broker2消费消息，当consumer2消费了15条消息时，broker2挂掉了。 但是还剩下15条消息在broker2上面，这些消息就好像消息了，除非broker2重启了，然后有消费者连接到broker2上来消费消息，遇到这样的情况该怎么办呢？

　　从5.6版本起，在destinationPolicy上新增的选择replayWhenNoConsumers，这个选项使得broker2上有需要转发的消息但是没有消费者时，把消息回流到它原来的broker1上，同时需要把enableAudit设置为false,为了防止消息回流后被当做重复消息而不被分发，activemq.xml配置如下：

配置允许双向连接

先运行发送消息程序，然后运行61716端口的程序接收消息，再接收了5条后将程序断掉，再去运行61616端口的程序，也是可以接收消息的，这样就实现了消息的回流。

消息发送程序：

 import javax.jms.Connection;
 import javax.jms.ConnectionFactory;
 import javax.jms.Destination;
 import javax.jms.MessageProducer;
 import javax.jms.Session;
 import javax.jms.TextMessage;

 import org.apache.activemq.ActiveMQConnectionFactory;

 public class JmsSend {
     public static void main(String[] args) throws Exception {
         ConnectionFactory connectionFactory = new ActiveMQConnectionFactory("tcp://192.168.1.81:61616");
         Connection connection = connectionFactory.createConnection();
         connection.start();

         Session session = connection.createSession(Boolean.TRUE, Session.AUTO_ACKNOWLEDGE);
         Destination destination = session.createQueue("my-queue");

         MessageProducer producer = session.createProducer(destination);
         for(int i = 0;i < 10;i++){
             TextMessage message = session.createTextMessage("message,1212 --->" + i);
             Thread.sleep(1000);
             //通过生产者发出消息
             producer.send(message);
         }
         session.commit();
         session.close();
         connection.close();
     }
 }

61616端口接收消息程序：

 import javax.jms.Connection;
 import javax.jms.ConnectionFactory;
 import javax.jms.Destination;
 import javax.jms.MessageConsumer;
 import javax.jms.Session;
 import javax.jms.TextMessage;

 import org.apache.activemq.ActiveMQConnectionFactory;

 public class JmsReceiver {
     public static void main(String[] args) throws Exception {
         ConnectionFactory cf = new ActiveMQConnectionFactory("tcp://192.168.1.81:61616");
         Connection connection =  cf.createConnection();
         connection.start();

         Session session = connection.createSession(Boolean.TRUE, Session.AUTO_ACKNOWLEDGE);
         Destination destination = session.createQueue("my-queue");
         MessageConsumer consumer = session.createConsumer(destination);
         int i = 0;
         while(i < 10){
             Thread.sleep(3000);
             i++;
             TextMessage message = (TextMessage)consumer.receive();
             session.commit();
             System.out.println("111接收到的消息是:"+message.getText());
         }
         session.close();
         connection.close();
     }
 }

61716端口接收消息程序：

 import javax.jms.Connection;
 import javax.jms.ConnectionFactory;
 import javax.jms.Destination;
 import javax.jms.MessageConsumer;
 import javax.jms.Session;
 import javax.jms.TextMessage;

 import org.apache.activemq.ActiveMQConnectionFactory;

 public class JmsReceiver2 {
     public static void main(String[] args) throws Exception {
         ConnectionFactory cf = new ActiveMQConnectionFactory("tcp://192.168.1.81:61716");
         Connection connection =  cf.createConnection();
         connection.start();

         Session session = connection.createSession(Boolean.TRUE, Session.AUTO_ACKNOWLEDGE);
         Destination destination = session.createQueue("my-queue");
         MessageConsumer consumer = session.createConsumer(destination);
         int i = 0;
         while(i < 10){
             Thread.sleep(3000);
             i++;
             TextMessage message = (TextMessage)consumer.receive();
             session.commit();
             System.out.println("222接收到的消息是:"+message.getText());
         }
         session.close();
         connection.close();
     }
 }