信息发布与订阅

        Rabbit的核心组件包含Queue(消息队列)和Exchanges两部分，Exchange的主要部分就是对信息进行路由，通过将消息队列绑定到Exchange上，则可以实现订阅形式的消息发布及Publish/Subscribe在这种模式下消息发布者只需要将信息发布到相应的Exchange中，而Exchange则自动将信息分发到不同的Queue当中。

    这种模式下Exchange充当的角色

    在命令行中可以使用

    sudo rabbitmqctl list_exchanges

    sudo rabbitmqctl list_bindings

    分别查看当前系统种存在的Exchange和Exchange上绑定的Queue信息。

    消息发布者EmitLog.java

import com.rabbitmq.client.Channel;  import com.rabbitmq.client.Connection;  import com.rabbitmq.client.ConnectionFactory;    public class EmitLog {     private static final String  EXCHANGE_NAME="logs";      public static void main(String[] args) throws java.io.IOException{        //创建链接工厂    ConnectionFactory factory = new ConnectionFactory();    factory.setHost("localhost");    //创建链接    Connection connection = factory.newConnection();        //创建信息管道    Channel channel = connection.createChannel();        //生命Exchange 非持久化    channel.exchangeDeclare(EXCHANGE_NAME, "fanout");        String message = "Message "+Math.random();        //第一个参数是对应的Exchange名称,如果为空则使用默认Exchange    channel.basicPublish(EXCHANGE_NAME, "", null, message.getBytes());    System.out.println("[x] Sent '"+message+"'");        //关闭链接    channel.close();    connection.close();       }     }

    消息消费者ReceiveLogs.java

import java.io.IOException;    import com.rabbitmq.client.Channel;  import com.rabbitmq.client.Connection;  import com.rabbitmq.client.ConnectionFactory;  import com.rabbitmq.client.ConsumerCancelledException;  import com.rabbitmq.client.QueueingConsumer;  import com.rabbitmq.client.ShutdownSignalException;    public class ReceiveLogs {     private static final String EXCHANGE_NAME = "logs";     public static void main(String[] args) throws IOException, ShutdownSignalException, ConsumerCancelledException, InterruptedException {      //创建链接工厂    ConnectionFactory factory = new ConnectionFactory();    factory.setHost("localhost");    //创建链接    Connection connection = factory.newConnection();        //创建消息管道    Channel channel = connection.createChannel();      //声明Exchange    channel.exchangeDeclare(EXCHANGE_NAME, "fanout");        //利用系统自动声明一个非持久化的消息队列，并返回唯一的队列名称    String queueName = channel.queueDeclare().getQueue();      //将消息队列绑定到Exchange    channel.queueBind(queueName, EXCHANGE_NAME, "");      System.out.println(" [*] Waiting for messages. To exit press CTRL+C");      //声明一个消费者    QueueingConsumer consumer = new QueueingConsumer(channel);    channel.basicConsume(queueName, true, consumer);      while (true) {          //循环获取信息     QueueingConsumer.Delivery delivery = consumer.nextDelivery();     String message = new String(delivery.getBody());     System.out.println(" [x] Received '" + message + "'");         }     }    }

    运行时启动一个EmitLog.java多个ReceiveLogs.java则可以看到发布者每次发布信息，只要绑定到了相应Exchange的消费者都可以获取到信息。

RabbitMQ信息持久化技术

    上面的例子中我们实现了Publisher/Subscribe的消息分发方式，但是其中存在一些问题。比如当我们运行一个ReceiveLog都对应了一个特定的消息队列，可以利用list_queues进行查看，同时这些消息队列是帮到到名为logs的Exchange中，这是发布消息每个消费者都可以接收到，可以当关闭ReceiveLog程序后这些消息队列就都会自动销毁，因为他们是非持久化的。同样对于EmitLog程序也一样，每次关闭后之前生命的Exchange也将自动销毁。

    这就产生了一些问题。如果当ReceiveLog为运行时，此时就并没有一个消息队列是绑定到Exchange上的，在发布消息后再启动ReceiveLog程序是无法接受到之前发布的信息。这就是为什么要进行消息的持久化。

    通过持久化技术，我们可以生命一个持久化的Exchange，以及持久化的Queue这样，在把Queue绑定到Exchange后，即使没有消费者程序运行，信息依然能保存在Queue当中，当下次启动消费者程序时依然能获取到发布的所有信息。就好比当一个消费者程序在执行消息序列中的任务时，如果突然出现了异常那么重新启动后，依然能从上一次发生错误的位置继续运行，对于某些需要一个有序性和连续性的操作，这点显的尤为重要。

    下面还是给出一个例子，在持久化过程中，可以借助list_exchanges,list_bindings,list_queues来查看服务器中相关信息来帮组分析过程。

    Publisher.java

import com.rabbitmq.client.Channel;  import com.rabbitmq.client.Connection;  import com.rabbitmq.client.ConnectionFactory;  import com.rabbitmq.client.MessageProperties;    public class Publisher {      private static final String  EXCHANGE_NAME="persi";//定义Exchange名称   private static final boolean durable = true;//消息队列持久化      public static void main(String[] args) throws java.io.IOException {      ConnectionFactory factory = new ConnectionFactory();//创建链接工厂    factory.setHost("localhost");    Connection connection = factory.newConnection();//创建链接    Channel channel = connection.createChannel();//创建信息通道                      channel.exchangeDeclare(EXCHANGE_NAME, "fanout", durable);//创建交换机并生命持久化      String message = "Hello Wrold "+Math.random();                  //消息的持久化    channel.basicPublish(EXCHANGE_NAME, "", MessageProperties.PERSISTENT_TEXT_PLAIN, message.getBytes());        System.out.println("[x] Sent '" + message + "'");      channel.close();    connection.close();     }     }

    Subscriber.java

public class Subscriber {        //private static final String[] QUEUE_NAMES= {"que_001","que_002","que_003","que_004","que_005"};   private static final String[] QUEUE_NAMES= {"que_006","que_007","que_008","que_009","que_0010"};      public static void main(String[] args){      for(int i=0;i<QUEUE_NAMES.length;i++){          SubscriberThead sub = new SubscriberThead(QUEUE_NAMES[i]);     Thread t = new Thread(sub);     t.start();         }       }  }

    SubscriberThead.java

import com.rabbitmq.client.Channel;  import com.rabbitmq.client.Connection;  import com.rabbitmq.client.ConnectionFactory;  import com.rabbitmq.client.QueueingConsumer;  import com.rabbitmq.client.AMQP.Queue.DeclareOk;    public class SubscriberThead implements Runnable {     private String queue_name = null;   private static final String EXCHANGE_NAME = "persi";// 定义交换机名称   private static final boolean durable = true;//消息队列持久化      public SubscriberThead(String queue_name) {        this.queue_name = queue_name;      }     @Override   public void run() {      try{        ConnectionFactory factory = new ConnectionFactory();    factory.setHost("localhost");    Connection connection = factory.newConnection();    Channel channel = connection.createChannel();      channel.exchangeDeclare(EXCHANGE_NAME, "fanout", durable);      DeclareOk ok = channel.queueDeclare(queue_name, durable, false,      false, null);    String queueName = ok.getQueue();          channel.queueBind(queueName, EXCHANGE_NAME, "");      System.out.println(" ["+queue_name+"] Waiting for messages. To exit press CTRL+C");      channel.basicQos(1);//消息分发处理    QueueingConsumer consumer = new QueueingConsumer(channel);    channel.basicConsume(queueName, false, consumer);      while (true) {       Thread.sleep(2000);     QueueingConsumer.Delivery delivery = consumer.nextDelivery();     String message = new String(delivery.getBody());     System.out.println(" ["+queue_name+"] Received '" + message + "'");     channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);      }    }catch(Exception e){          e.printStackTrace();    }         }    }

    通过持久化处理后rabbitMQ将保存Exchange信息以及Queue信息，甚至在rabbitMQ服务器关闭后信息依然能保存，这样就提供了消息传递的可靠性