rabbitmq学习2:Work Queues

 在前面的已经提到了一对一的情况;现在一个生产者与多个消费者的情况（Work Queues）。
Work Queues的示意图如下：

 

对于上图的模型中对于c端的worker来说。RabbitMQ服务器可能一直发送多个消息给一个worker，而另一个可能几乎不做任何事情。这样就会导致一个worker很忙，而另一个却很空闲。这种情况可能都不想出现。如何解决这个问题呢。当然最理想的情况是均匀分配消息给每个worker。我们可能通过channel . basicQos(1)方法（prefetchCount = 1 ）来设置同一时间每次发给一个消息给一个worker。示意图如下：

 

P端的程序如下：

 package com.abin.rabbitmq;

 import com.rabbitmq.client.Channel;
 import com.rabbitmq.client.Connection;
 import com.rabbitmq.client.ConnectionFactory;
 import com.rabbitmq.client.MessageProperties;

 public class NewTask {
     private static final String TASK_QUEUE_NAME = "task_queue";

     public static void main(String[] argv) throws Exception {

         ConnectionFactory factory = new ConnectionFactory();
         factory.setHost("localhost");
         Connection connection = factory.newConnection();
         Channel channel = connection.createChannel();
         //声明此队列并且持久化
         channel.queueDeclare(TASK_QUEUE_NAME, true, false, false, null);

         String message = getMessage(argv);

         channel.basicPublish("", TASK_QUEUE_NAME,
                 MessageProperties.PERSISTENT_TEXT_PLAIN, message.getBytes());//持久化消息
         System.out.println(" [x] Sent '" + message + "'");

         channel.close();
         connection.close();
     }

     private static String getMessage(String[] strings) {
         if (strings.length < 1)
             return "Hello World!";
         return joinStrings(strings, " ");
     }

     private static String joinStrings(String[] strings, String delimiter) {
         int length = strings.length;
         if (length == 0)
             return "";
         StringBuilder words = new StringBuilder(strings[0]);
         for (int i = 1; i < length; i++) {
             words.append(delimiter).append(strings[i]);
         }
         return words.toString();
     }
 }

    多次运行此程序并传入的参数分别为“First message ”，“Secondmessage ”，“Third message ”，“Fourth message ”，“Fifth message ”

 

C端的程序如下：

 package com.abin.rabbitmq;

 import com.rabbitmq.client.Channel;
 import com.rabbitmq.client.Connection;
 import com.rabbitmq.client.ConnectionFactory;
 import com.rabbitmq.client.QueueingConsumer;

 public class Worker {
     private static final String TASK_QUEUE_NAME = "task_queue";
     public static void main(String[] argv) throws Exception {
         ConnectionFactory factory = new ConnectionFactory();
         factory.setHost("localhost");
         Connection connection = factory.newConnection();
         Channel channel = connection.createChannel();
         //声明此队列并且持久化
         channel.queueDeclare(TASK_QUEUE_NAME, true, false, false, null);
         System.out.println(" [*] Waiting for messages. To exit press CTRL+C");

         channel.basicQos(1);//告诉RabbitMQ同一时间给一个消息给消费者
         /* We're about to tell the server to deliver us the messages from the queue.
          * Since it will push us messages asynchronously,
          * we provide a callback in the form of an object that will buffer the messages
          * until we're ready to use them. That is what QueueingConsumer does.*/
         QueueingConsumer consumer = new QueueingConsumer(channel);
         /*
           把名字为TASK_QUEUE_NAME的Channel的值回调给QueueingConsumer,即使一个worker在处理消息的过程中停止了，这个消息也不会失效
         */
         channel.basicConsume(TASK_QUEUE_NAME, false, consumer);

         while (true) {
             QueueingConsumer.Delivery delivery = consumer.nextDelivery();//得到消息传输信息
             String message = new String(delivery.getBody());

             System.out.println(" [x] Received '" + message + "'");
             doWork(message);
             System.out.println(" [x] Done");

             channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);//下一个消息
         }
     }

     private static void doWork(String task) throws InterruptedException {
         for (char ch : task.toCharArray()) {
             if (ch == '.')
                 Thread.sleep(1000);//这里是假装我们很忙
         }
     }
 }

  开启两个worker分别运行。运行结果如：

c1的结果：

 [*] Waiting for messages. To exit press CTRL+C
  [x] Received 'First message'
  [x] Received 'Third message'
  [x] Received 'Fifth message'

 c2的结果

 [*] Waiting for messages. To exit press CTRL+C
  [x] Received 'Second message'
  [x] Received 'Fourth message'