详解SpringBoot中使用RabbitMQ的RPC功能

一、RabbitMQ的RPC简介

实际业务中，有的时候我们还需要等待消费者返回结果给我们，或者是说我们需要消费者上的一个功能、一个方法或是一个接口返回给我们相应的值，而往往大型的系统软件，生产者跟消费者之间都是相互独立的两个系统，部署在两个不同的电脑上，不能通过直接对象.方法的形式获取想要的结果，这时候我们就需要用到RPC（Remote Procedure Call）远程过程调用方式。
RabbitMQ实现RPC的方式很简单，生产者发送一条带有标签（消息ID（correlation_id）+回调队列名称）的消息到发送队列，消费者（也称RPC服务端）从发送队列获取消息并处理业务，解析标签的信息将业务结果发送到指定的回调队列，生产者从回调队列中根据标签的信息获取发送消息的返回结果。

如图，客户端C发送消息，指定消息的ID=rpc_id，回调响应的队列名称为rpc_resp，消息从C发送到rpc_request队列，服务端S获取消息业务处理之后，将correlation_id附加到响应的结果发送到指定的回调队列rpc_resp中，客户端从回调队列获取消息，匹配与发送消息的correlation_id相同的值为消息应答结果。

二、SpringBoot中使用RabbitMQ的RPC功能

注意：springboot中使用的时候，correlation_id为系统自动生成的，reply_to在加载AmqpTemplate实例的时候设置的。

实例：
说明：队列1为发送队列，队列2为返回队列

1.先配置rabbitmq

package com.ws.common;

import org.springframework.amqp.core.Binding;
import org.springframework.amqp.core.BindingBuilder;
import org.springframework.amqp.core.Queue;
import org.springframework.amqp.core.TopicExchange;
import org.springframework.amqp.rabbit.connection.CachingConnectionFactory;
import org.springframework.amqp.rabbit.connection.ConnectionFactory;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/*
 * rabbitMQ配置类
 */
@Configuration
public class RabbitMQConfig {
	public static final String TOPIC_QUEUE1 = "topic.queue1";
    public static final String TOPIC_QUEUE2 = "topic.queue2";
    public static final String TOPIC_EXCHANGE = "topic.exchange";

    @Value("${spring.rabbitmq.host}")
    private String host;
    @Value("${spring.rabbitmq.port}")
    private int port;
    @Value("${spring.rabbitmq.username}")
    private String username;
    @Value("${spring.rabbitmq.password}")
    private String password;

    @Autowired
    ConnectionFactory connectionFactory;

    @Bean(name = "connectionFactory")
    public ConnectionFactory connectionFactory() {
    	CachingConnectionFactory connectionFactory = new CachingConnectionFactory();
    	connectionFactory.setHost(host);
    	connectionFactory.setPort(port);
    	connectionFactory.setUsername(username);
    	connectionFactory.setPassword(password);
    	connectionFactory.setVirtualHost("/");
    	return connectionFactory;
    }

    @Bean
    public RabbitTemplate rabbitTemplate() {
    	RabbitTemplate rabbitTemplate = new RabbitTemplate(connectionFactory);
    	//设置reply_to（返回队列，只能在这设置）
    	rabbitTemplate.setReplyAddress(TOPIC_QUEUE2);
    	rabbitTemplate.setReplyTimeout(60000);
    	return rabbitTemplate;
    }
    //返回队列监听器（必须有）
    @Bean(name="replyMessageListenerContainer")
    public SimpleMessageListenerContainer createReplyListenerContainer() {
         SimpleMessageListenerContainer listenerContainer = new SimpleMessageListenerContainer();
         listenerContainer.setConnectionFactory(connectionFactory);
         listenerContainer.setQueueNames(TOPIC_QUEUE2);
         listenerContainer.setMessageListener(rabbitTemplate());
         return listenerContainer;
    }

    //创建队列
    @Bean
    public Queue topicQueue1() {
        return new Queue(TOPIC_QUEUE1);
    }
    @Bean
    public Queue topicQueue2() {
        return new Queue(TOPIC_QUEUE2);
    }

    //创建交换机
    @Bean
    public TopicExchange topicExchange() {
        return new TopicExchange(TOPIC_EXCHANGE);
    }

    //交换机与队列进行绑定
    @Bean
    public Binding topicBinding1() {
        return BindingBuilder.bind(topicQueue1()).to(topicExchange()).with(TOPIC_QUEUE1);
    }
    @Bean
    public Binding topicBinding2() {
        return BindingBuilder.bind(topicQueue2()).to(topicExchange()).with(TOPIC_QUEUE2);
    }
}

2.发送消息并同步等待返回值

@Autowired
private RabbitTemplate rabbitTemplate;

//报文body
String sss = "报文的内容";
//封装Message
Message msg = this.con(sss);
log.info("客户端--------------------"+msg.toString());
//使用sendAndReceive方法完成rpc调用
Message message=rabbitTemplate.sendAndReceive(RabbitMQConfig.TOPIC_EXCHANGE, RabbitMQConfig.TOPIC_QUEUE1, msg);
//提取rpc回应内容body
String response = new String(message.getBody());
log.info("回应：" + response);
log.info("rpc完成---------------------------------------------");

public Message con(String s) {
	MessageProperties mp = new MessageProperties();
	byte[] src = s.getBytes(Charset.forName("UTF-8"));
	//mp.setReplyTo("adsdas");   加载AmqpTemplate时设置，这里设置没用
	//mp.setCorrelationId("2222");   系统生成，这里设置没用
	mp.setContentType("application/json");
	mp.setContentEncoding("UTF-8");
	mp.setContentLength((long)s.length());
	return new Message(src, mp);
}

3.写消费者

package com.ws.listener.mq;

import java.nio.charset.Charset;

import org.springframework.amqp.core.Message;
import org.springframework.amqp.core.MessageProperties;
import org.springframework.amqp.rabbit.annotation.RabbitListener;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import com.ws.common.RabbitMQConfig;

import lombok.extern.slf4j.Slf4j;

@Slf4j
@Component
public class Receiver {
	@Autowired
	private RabbitTemplate rabbitTemplate;

	@RabbitListener(queues=RabbitMQConfig.TOPIC_QUEUE1)
	public void receiveTopic1(Message msg) {
		log.info("队列1:"+msg.toString());
		String msgBody = new String(msg.getBody());
		//数据处理，返回的Message
		Message repMsg = con(msgBody+"返回了", msg.getMessageProperties().getCorrelationId());

		rabbitTemplate.send(RabbitMQConfig.TOPIC_EXCHANGE, RabbitMQConfig.TOPIC_QUEUE2, repMsg);

    }
	@RabbitListener(queues=RabbitMQConfig.TOPIC_QUEUE2)
	public void receiveTopic2(Message msg) {
		log.info("队列2:"+msg.toString());

    }

	public Message con(String s, String id) {
		MessageProperties mp = new MessageProperties();
		byte[] src = s.getBytes(Charset.forName("UTF-8"));
		mp.setContentType("application/json");
		mp.setContentEncoding("UTF-8");
		mp.setCorrelationId(id);

		return new Message(src, mp);
	}
}

日志打印：

2019-06-26 17:11:16.607 [http-nio-8080-exec-4] INFO com.ws.controller.UserController - 客户端--------------------(Body:‘报文的内容' MessageProperties [headers={}, contentType=application/json, contentEncoding=UTF-8, contentLength=5, deliveryMode=PERSISTENT, priority=0, deliveryTag=0])

2019-06-26 17:11:16.618 [SimpleAsyncTaskExecutor-1] INFO com.ws.listener.mq.Receiver - 队列1:(Body:‘报文的内容' MessageProperties [headers={}, correlationId=1, replyTo=topic.queue2, contentType=application/json, contentEncoding=UTF-8, contentLength=0, receivedDeliveryMode=PERSISTENT, priority=0, redelivered=false, receivedExchange=topic.exchange, receivedRoutingKey=topic.queue1, deliveryTag=1, consumerTag=amq.ctag-8IzlhblYmTebqUYd-uferw, consumerQueue=topic.queue1])

2019-06-26 17:11:16.623 [http-nio-8080-exec-4] INFO com.ws.controller.UserController - 回应：报文的内容返回了

2019-06-26 17:11:16.623 [http-nio-8080-exec-4] INFO com.ws.controller.UserController - rpc完成---------------------------------------------

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