第一章 说明

Spring Boot Messaging
Spring框架提供了与消息传递系统集成的广泛支持，从使用JmsTemplate简化JMS API到异步接收消息的完整基础结构。Spring AMQP为高级消息队列协议提供了类似的特性集。Spring Boot还为RabbitTemplate和RabbitMQ提供了自动配置选项。Spring WebSocket本身就支持STOMP消息传递，Spring Boot通过启动器和少量的自动配置支持这一点。Spring Boot也支持Apache Kafka。

AMQP
高级消息队列协议(Advanced Message queue Protocol, AMQP)是面向消息中间件的平台无关的、线级协议。Spring AMQP项目将核心Spring概念应用于基于AMQP的消息传递解决方案的开发。Spring Boot为通过RabbitMQ使用AMQP提供了一些便利，包括Spring-Boot-Starter-AMQP“Starter”。

RabbitMQ 扩展
RabbitMQ是一个基于AMQP协议的轻量级、可靠、可伸缩和可移植的消息代理。Spring使用RabbitMQ通过AMQP协议进行通信。

第二章 编写代码

2.1 启动 RabbitMQ

安装 RabbitMQ 服务，以 Mac 为例

brew install rabbitmq

等待安装完成后，进入安装目录 '/usr/local/Cellar/rabbitmq/3.7.4/sbin'，启动

cd /usr/local/Cellar/rabbitmq/3.7.4/sbin
./rabbitmq-server

如果启动成功，将会看到

  ##  ##
  ##  ##      RabbitMQ 3.7.4. Copyright (C) 2007-2018 Pivotal Software, Inc.
  ##########  Licensed under the MPL.  See http://www.rabbitmq.com/
  ######  ##
  ##########  Logs: /usr/local/var/log/rabbitmq/rabbit@localhost.log
                    /usr/local/var/log/rabbitmq/rabbit@localhost_upgrade.log

              Starting broker...
 completed with 6 plugins.

2.2 代码

2.2.1 文件结构

src/
 +- main/
     +- java/
         +- com/
             +- lee/
                 +- springbootdemo/
                     +- config
                         +- RabbitMQConfig.java
                     +- pojo/
                         +- Receiver.java
                         +- Runner.java
                     +- SpringBootDemoApplication.java
     +- resources/
         +- <other resource>

2.2.2 创建 RabbitMQ 消息接受

src/main/java/com/lee/springbootdemo/pojo/Receiver.java

package com.lee.springbootdemo.pojo;

import org.springframework.stereotype.Component;
import java.util.concurrent.CountDownLatch;

@Component
public class Receiver {

    private CountDownLatch latch = new CountDownLatch(1);

    public void receiveMessage(String message) {
        System.out.println("Received <" + message + ">");
        latch.countDown();
    }

    public CountDownLatch getLatch() {
        return latch;
    }
}

2.2.3 注册监听和发送消息

src/main/java/com/lee/springbootdemo/config/RabbitMQConfig.java

package com.lee.springbootdemo.config;

import com.lee.springbootdemo.pojo.Receiver;
import org.springframework.amqp.core.*;
import org.springframework.amqp.rabbit.connection.ConnectionFactory;
import org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer;
import org.springframework.amqp.rabbit.listener.adapter.MessageListenerAdapter;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class RabbitMQConfig {

    public static final String topicExchangeName = "spring-boot-exchange";
    public static final String queueName = "spring-boot";

    @Bean
    public Queue queue() {
        return new Queue(queueName, false);
    }

    @Bean
    public DirectExchange exchange() {
        return new DirectExchange(topicExchangeName);
    }

    @Bean
    public Binding binding(Queue queue, DirectExchange exchange) {
        return BindingBuilder.bind(queue).to(exchange).with("foo.bar.#");
    }

    @Bean
    public SimpleMessageListenerContainer container(ConnectionFactory connectionFactory, MessageListenerAdapter listenerAdapter) {
        SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
        container.setConnectionFactory(connectionFactory);
        container.setQueueNames(queueName);
        container.setMessageListener(listenerAdapter);

        return container;
    }

    @Bean
    public MessageListenerAdapter listenerAdapter(Receiver receiver) {
        return new MessageListenerAdapter(receiver, "receiveMessage");
    }
}

• queue() 方法创建一个 AMQP 队列

• exchange() 方法创建一个 direct 交换器

• binding() 方法把上面两个内容绑定在一起，定义 RabbitTemplate 发布消息的行为

  Spring AMQP要求将队列、TopicExchange和绑定声明为顶级Spring bean，以便正确设置。

• 在这里，我们把 direct exchange 和 queue 绑定的路由键（routing key）是 foo.bar.#

2.2.4 测试发布消息

src/main/java/com/lee/springbootdemo/pojo/Runner.java

package com.lee.springbootdemo.pojo;

import com.lee.springbootdemo.config.RabbitMQConfig;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;
import java.util.concurrent.TimeUnit;

@Component
public class Runner implements CommandLineRunner {

    private final RabbitTemplate rabbitTemplate;
    private final Receiver receiver;

    public Runner(Receiver receiver, RabbitTemplate rabbitTemplate) {
        this.rabbitTemplate = rabbitTemplate;
        this.receiver = receiver;
    }

    @Override
    public void run(String... args) throws Exception {
        System.out.println("Sending message ...");
        rabbitTemplate.convertAndSend(RabbitMQConfig.topicExchangeName, "foo.bar.baz", "Hello from RabbitMQ!");
        receiver.getLatch().await(10000, TimeUnit.MILLISECONDS);
    }
}

这里我们定义的路由键（routing key）是foo.bar.baz

2.2.5 运行

运行 SpringBootDemoApplication.main() 方法，如果运行成功，将会看到

Sending message ...
Received <Hello from RabbitMQ!>

附录 A 参考

1. Spring Boot Messaging 官方文档
2. Spring Messaging 代码案例

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