四、RabbitMQ之工作队列(Work Queue)之轮询分发(Round-Robin)

一、模型

Work Queue模型

P(producer)：生产者——发送消息
Q(Queue)：消息队列(图中红色方形)——存储消息
C(consumer): 消费者——接收消息

轮询分发(Round-Robin)即消费者1(C1)从队列(Queue)中获取一条消息之后，消费者2(C2)再从队列(Queue)中获取一条消息，等消费者2(C2)获取完之后又轮到消费者1(C1)获取，如此轮流获取，与业务时长无关，保证两个消费者获得的消息是均衡的。

二、为何会有工作队列(Work Queue)的出现

简单队列（Simple Queue）是一一对应的，而且我们实际开发中，生产者发送消息是毫不费力的，但消费者一般是跟业务相结合的，消费者接收到消息之后就需要处理，可能需要花费一定的时间，这时候队列就会积压了很多消息。

三、Java编程实现

1、导入AMQP协议jar包，以及创建RabbitMQ连接工具类，请查看三、RabbitMQ之简单队列(Simple Queue)；

2、创建生产者发送消息；

package com.rabbitMQ.work;

import java.io.IOException;
import java.util.concurrent.TimeoutException;

import com.rabbitMQ.util.ConnectionUtils;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;

/**
 * 工作队列-生产者
 * @author zhoujin
 * @data 2019-1-16
 */
public class WorkProducer {
	
	private static final String QUEUE_NAME = "work_queue";
	
	public static void main(String[] args) {
		Connection conn = null;
		Channel channel = null;
		try {
			// 1.获取连接
			conn = ConnectionUtils.getConnection();
			// 2.从连接中获取通道
			channel = conn.createChannel();
			// 3.申明队列
			channel.queueDeclare(QUEUE_NAME, false, false, false, null);
			// 4.发送消息入队列
			for (int i = 1; i <= 20; i++) {
				String message = "This is work queue, 发送第" + i + "条消息!";
				channel.basicPublish("", QUEUE_NAME, null, message.getBytes());
				
				Thread.sleep(i * 200);
			}
			
			System.out.println("======================= Work Queue send message end! =======================");
			
		} catch (IOException e) {
			e.printStackTrace();
		} catch (TimeoutException e) {
			e.printStackTrace();
		} catch (InterruptedException e) {
			e.printStackTrace();
		} finally {
			// 5.关闭通道以及连接
			try {
				ConnectionUtils.closeConnection(channel, conn);
			} catch (IOException e) {
				e.printStackTrace();
			} catch (TimeoutException e) {
				e.printStackTrace();
			}
		}

	}

}

3、创建消费者1接收消息；

package com.rabbitMQ.work;

import java.io.IOException;
import java.util.concurrent.TimeoutException;

import com.rabbitMQ.util.ConnectionUtils;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;
import com.rabbitmq.client.AMQP.BasicProperties;

/**
 * 工作队列-消费者1
 * @author zhoujin
 * @data 2019-1-17
 */
public class WorkFirstConsumer {
	
	private static final String QUEUE_NAME = "work_queue";
	
	public static void main(String[] args) {
		try {
			// 1.获取连接
			Connection conn = ConnectionUtils.getConnection();
			// 2.从连接中获取通道
			Channel channel = conn.createChannel();
			// 3.声明队列
			channel.queueDeclare(QUEUE_NAME, false, false, false, null);
			// 4.创建消费者
			DefaultConsumer consumer = new DefaultConsumer(channel){
				@Override
				public void handleDelivery(String consumerTag,
						Envelope envelope, BasicProperties properties,
						byte[] body) throws IOException {
					
					String message = new String(body, "UTF-8");
					System.out.println("======================= The first consumer received a message! 【Content:" + message + "】 =======================");
					
					// 休眠，模拟业务处理
					try {
						Thread.sleep(2000);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			};
			// 5.监听队列
			channel.basicConsume(QUEUE_NAME, true, consumer);
			
		} catch (IOException e) {
			e.printStackTrace();
		} catch (TimeoutException e) {
			e.printStackTrace();
		}

	}

}

4、创建消费者2接收消息。

package com.rabbitMQ.work;

import java.io.IOException;
import java.util.concurrent.TimeoutException;

import com.rabbitMQ.util.ConnectionUtils;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;
import com.rabbitmq.client.AMQP.BasicProperties;

/**
 * 工作队列-消费者2
 * @author zhoujin
 * @data 2019-1-17
 */
public class WorkSecondConsumer {
	
	private static final String QUEUE_NAME = "work_queue";

	public static void main(String[] args) {
		try {
			// 1.获取连接
			Connection conn = ConnectionUtils.getConnection();
			// 2.从连接中获取通道
			Channel channel = conn.createChannel();
			// 3.声明队列
			channel.queueDeclare(QUEUE_NAME, false, false, false, null);
			// 4.创建消费者
			DefaultConsumer consumer = new DefaultConsumer(channel){
				@Override
				public void handleDelivery(String consumerTag,
						Envelope envelope, BasicProperties properties,
						byte[] body) throws IOException {
					
					String message = new String(body, "UTF-8");
					System.out.println("======================= The second consumer received a message! 【Content:" + message + "】 =======================");
					
					// 休眠，模拟业务处理
					try {
						Thread.sleep(1000);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			};
			// 5.监听队列
			channel.basicConsume(QUEUE_NAME, true, consumer);
			
		} catch (IOException e) {
			e.printStackTrace();
		} catch (TimeoutException e) {
			e.printStackTrace();
		}
	}
	
}