RabbitMQ-队列

上一篇文章,写了一个小demo, 用于发送和接收消息,下面创建一个工作队列,向多个消费者分发耗时的任务

图是这样子的

代码学习

生产者

package com.tgb.kwy.workqueues;

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

/**
 * Description
 *生产
 * @author kongwy [e-mail]
 * @version 1.0
 * @date 2018-07-08-20 -58
 */
public class NewTask {
    private static final String TASK_QUEUE_NAME="task_queue";

    public static void main(String[] args) throws Exception{
        ConnectionFactory factory=new ConnectionFactory();
        factory.setHost("192.168.159.132");/*设置rabbitmq所在主机ip或主机名*/
        /*指定用户名和密码*/
        factory.setUsername("admin");
        factory.setPassword("admin");
        Connection connection=factory.newConnection();
        Channel channel=connection.createChannel();
        channel.queueDeclare(TASK_QUEUE_NAME,true,false,false,null);
        String message = getMessage(args);

        channel.basicPublish("", TASK_QUEUE_NAME, MessageProperties.PERSISTENT_TEXT_PLAIN, message.getBytes("UTF-8"));
        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 = 0; i < length; i++) {
            words.append(delimiter).append(strings[i]);
        }
        return words.toString();
    }
}

消费者代码

package com.tgb.kwy.workqueues;

import com.rabbitmq.client.*;

import java.io.IOException;

/**
 * Description
 *
 * @author kongwy [e-mail]
 * @version 1.0
 * @date 2018-07-08-21 -03
 */
public class Worker {
    private static final String TASK_QUEUE_NAME="task_queue";

    public static void main(String[] args) throws Exception{
        ConnectionFactory factory=new ConnectionFactory();
        factory.setHost("192.168.159.132");/*设置rabbitmq所在主机ip或主机名*/
        /*指定用户名和密码*/
        factory.setUsername("admin");
        factory.setPassword("admin");
        final Connection connection=factory.newConnection();
        final Channel channel=connection.createChannel();
        //声明队列,主要为了防止消息接受者先运行此程序,队列还不存在时创建队列
        channel.queueDeclare(TASK_QUEUE_NAME,true,false,false,null);
        System.out.println(" [*] Waiting for messages. To exit press CTRL+C");
        //channel.basicQos(1); // accept only one unack-ed message at a time (see below)
        int prefetchCount=1;
        channel.basicQos(prefetchCount);
        final Consumer consumer=new DefaultConsumer(channel){
            @Override
            public void handleDelivery(String consumeTag,Envelope envelope,AMQP.BasicProperties properties,byte[] body)throws IOException{
                String message=new String(body,"UTF-8");
                System.out.println(" [x] Received '" + message + "'");
                try{
                    doWork(message);
                }finally {
                    System.out.println("[x] Done");
                    channel.basicAck(envelope.getDeliveryTag(),false);
                }
            }
        };
        boolean autoAck = true; // acknowledgment is covered below
        channel.basicConsume(TASK_QUEUE_NAME,autoAck,consumer);
    }
    private static void doWork(String task){
        for(char ch: task.toCharArray()){
            if(ch == '.'){
                try {
                    Thread.sleep(1000);
                }catch (InterruptedException _ignored){
                    Thread.currentThread().interrupt();
                }
            }
        }
    }
}

运行结果

任务分发

轮询分发

rabbitmq将逐个发送消息到序列中的写一个消费者,平均每个消费者获得的数量是相同的

Fair dispatch

如果这里有两个消费者的话,可能一个消费者非常的忙碌,但是另一个消费者,几乎一直闲着.但是rabbitmq,还是会均匀地发送消息. 因为当消息进入队列后, rabbitmq就会分配消息,不会看消费者未确认消息的数量.所以为了解决这个问题,就使用了basicQos(prefetchCount=1)方法,来限制rabbitmq只发不超过1条的消息给同一个消费者.当消费者处理完毕后,得到反馈,再发送下一次

注:代码来自官网.官网对于概念性的内容,讲解的还是很清楚的