SpringBoot框架下RabbitMQ消息接受功能的实现

一.概念

RabbitMQ是一个开源的实现AMQP的产品，SpringBoot为了实现RabbitMQ客户端的功能，提供了名字为spring-boot-starter-amqp的starter，开发者在pom或gradle文件中添加这个starter的依赖即可。

二.如何实现接受功能

为实现接受消息的功能，需要向springboot框架注册处理消息的方法，框架为此提供了两种利用java代码注册的方式

1.编程式注册处理消息。注册一个bean，实现RabbitListenerConfigurer接口

@Configuration          
          public class RabbitListenerConfig {                  
              return new RabbitListenerConfigurer() {
                  @Override
                  public void configureRabbitListeners(RabbitListenerEndpointRegistrar registrar) {
                      SimpleRabbitListenerEndpoint endpoint = new SimpleRabbitListenerEndpoint();
                      endpoint.setQueueNames("myQueue1", "myQueue2");
                      endpoint.setConcurrency("2");
                      endpoint.setMessageListener(message -> {
                           System.out.println("收到消息"+new String(message.getBody()));
                       });
                       registrar.registerEndpoint(endpoint);
                  }
              }
          }

2. 注册式处理消息的方法。使用@RabbitListener注解，在注册参数中设置需要监听的队列名字

@Component
public class MyRabbitReceiver {

    @RabbitListener(queues = {"myQueue1", "myQueue2"}, concurrency = "2")
    public void processMessage(Message message) {
        System.out.println("收到消息"+new String(message.getBody()));
    }
}

三.为什么能实现接收功能

• springboot项目启动时，默认扫描根目录下的META-INF/spring.factory文件，然后找到org.springframework.boot.autoconfigure.EnableAutoConfiguration对应的加载类，文件部分内容如下

  文件部分内容如下：

  org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
  org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
  org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
  

  可以看到框架会自动加载RabbitAutoConfiguration类

• RabbitAutoConfiguration伪代码如下：

  @Configuration  //表示这个是一个配置类
  @ConditionalOnClass({RabbitTemplate.class, Channel.class})  //表示classpath是否存在RabbitTemplate.class, Channel.class
  @EnableConfigurationProperties({RabbitProperties.class}) // 根据配置初始化RabbitProperties.class
  @Import({RabbitAnnotationDrivenConfiguration.class}) // 引入RabbitAnnotationDrivenConfiguration.class，用于初始化配置消息接收功能
  public class RabbitAutoConfiguration {
         //初始化ConnectionFactory bean
         @Configuration
         @ConditionalOnMissingBean(ConnectionFactory.class)
         protected static class RabbitConnectionFactoryCreator {
         }
         
         //初始化rabbitTemplate, RabbitAdmin bean
         @Configuration
         @Import({RabbitAutoConfiguration.RabbitConnectionFactoryCreator.class})
         protected static class RabbitTemplateConfiguration {
         }
         
         //初始化RabbitMessagingTemplate bean
         @Configuration
         @ConditionalOnClass({RabbitMessagingTemplate.class})
         @ConditionalOnMissingBean({RabbitMessagingTemplate.class})
         @Import({RabbitAutoConfiguration.RabbitTemplateConfiguration.class})
         protected static class MessagingTemplateConfiguration {
         }
     }
  

  • 初始化ConnectionFactory
  • 初始化rabbitTemplate、rabbitAdmin
  • 初始化rabbitMessagingTemplate

  RabbitAutoConfiguration还引入RabbitAnnotationDrivenConfiguration类

• RabbitAnnotationDrivenConfiguration

  @Configuration(
      proxyBeanMethods = false
  )
  @ConditionalOnClass({EnableRabbit.class})
  class RabbitAnnotationDrivenConfiguration {
      @Bean(
          name = {"rabbitListenerContainerFactory"}
      )
      @ConditionalOnMissingBean(
          name = {"rabbitListenerContainerFactory"}
      )
      @ConditionalOnProperty(
          prefix = "spring.rabbitmq.listener",
          name = {"type"},
          havingValue = "simple",
          matchIfMissing = true
      )
      SimpleRabbitListenerContainerFactory simpleRabbitListenerContainerFactory(SimpleRabbitListenerContainerFactoryConfigurer configurer, ConnectionFactory connectionFactory, ObjectProvider> simpleContainerCustomizer) {
      }
  
      @Configuration(
          proxyBeanMethods = false
      )
      @EnableRabbit
      @ConditionalOnMissingBean(
          name = {"org.springframework.amqp.rabbit.config.internalRabbitListenerAnnotationProcessor"}
      )
      static class EnableRabbitConfiguration {
          EnableRabbitConfiguration() {
          }
      }
  }
  

  添加了@EnableRabbit注解

• @EnableRabbit注解中通过导入RabbitListenerConfigurationSelector后导入了RabbitBootstrapConfiguration

  RabbitBootstrapConfiguration中想容器中添加了RabbitListenerAnnotationBeanPostProcessor实例

• RabbitListenerAnnotationBeanPostProcessor

  • 实现了SmartInitializingSingleton的接口，在IOC容器实例加载完成后，会调用afterSingletonsInstantiated方法，对应了编程式的消息接受实现

    public void afterSingletonsInstantiated() {
            this.registrar.setBeanFactory(this.beanFactory);
            if (this.beanFactory instanceof ListableBeanFactory) {
                Map instances = ((ListableBeanFactory)this.beanFactory).getBeansOfType(RabbitListenerConfigurer.class);
                Iterator var2 = instances.values().iterator();
    
                while(var2.hasNext()) {
                    RabbitListenerConfigurer configurer = (RabbitListenerConfigurer)var2.next();
                    configurer.configureRabbitListeners(this.registrar);
                }
            }
        }
    

  • 实现了BeanPostProcessor的postProcessAfterInitialization方法，在每个实例初始化完成后会调用postProcessAfterInitialization方法。

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        Class targetClass = AopUtils.getTargetClass(bean);
        RabbitListenerAnnotationBeanPostProcessor.TypeMetadata metadata = (RabbitListenerAnnotationBeanPostProcessor.TypeMetadata)this.typeCache.computeIfAbsent(targetClass, this::buildMetadata);
        RabbitListenerAnnotationBeanPostProcessor.ListenerMethod[] var5 = metadata.listenerMethods;
        int var6 = var5.length;
    
        for(int var7 = 0; var7 < var6; ++var7) {
            RabbitListenerAnnotationBeanPostProcessor.ListenerMethod lm = var5[var7];
            RabbitListener[] var9 = lm.annotations;
            int var10 = var9.length;
    
            for(int var11 = 0; var11 < var10; ++var11) {
                RabbitListener rabbitListener = var9[var11];
                this.processAmqpListener(rabbitListener, lm.method, bean, beanName);
            }
        }
    
        if (metadata.handlerMethods.length > 0) {
            this.processMultiMethodListeners(metadata.classAnnotations, metadata.handlerMethods, bean, beanName);
        }
    
        return bean;
    }
    

​ 至此mq消息接受功能的实现完成。

后续将会对Springboot和Rabbit如何建立connection，建立多少个connection，connection和channel的关系，接受功能中相关参数的意义及实现，接受消息的方法是否需要考虑线程安全问题，以及AMQP协议的深入学习！