Springboot RabbitMq源码解析之RabbitListener注解

本文链接：https://blog.youkuaiyun.com/qq_39470742/article/details/85111910

本文详细解析了Springboot中RabbitListener注解的使用，包括其在方法和类上的应用，以及如何通过RabbitListenerAnnotationBeanPostProcessor进行处理。文章介绍了EnableRabbit、RabbitBootstrapConfiguration、RabbitListenerAnnotationBeanPostProcessor的工作流程，重点解析了RabbitListener注解的解析过程，涉及到RabbitListenerEndpointRegistrar和RabbitListenerEndpointRegistry的注册与启动。

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Springboot RabbitMq源码解析之配置类
 Springboot RabbitMq源码解析之消息发送
 Springboot RabbitMq源码解析之消费者容器SimpleMessageListenerContainer
Springboot RabbitMq源码解析之consumer管理和AmqpEvent

RabbitListener是Springboot RabbitMq中经常用到的一个注解，将被RabbitListener注解的类和方法封装成MessageListener注入MessageListenerContainer。
（1）当RabbitListener注解在方法上时，对应的方式就是Rabbit消息的监听器。
（2）当RabbitListener注解在类上时，和RabbitHandle注解配合使用，可以实现不同类型的消息的分发，类中被RabbitHandle注解的方法就是Rabbit消息的监听器。

一、EnableRabbit和RabbitBootstrapConfiguration

在Springboot RabbitMq源码解析之配置类已经提到，在springboot项目中已经通过自动配置类RabbitAutoConfiguration将EnableRabbit引入，而EnableRabbit又通过import注解引入了配置类RabbitBootstrapConfiguration。

@Configuration
public class RabbitBootstrapConfiguration {

	@Bean(name = RabbitListenerConfigUtils.RABBIT_LISTENER_ANNOTATION_PROCESSOR_BEAN_NAME)
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public RabbitListenerAnnotationBeanPostProcessor rabbitListenerAnnotationProcessor() {
		return new RabbitListenerAnnotationBeanPostProcessor();
	}

	@Bean(name = RabbitListenerConfigUtils.RABBIT_LISTENER_ENDPOINT_REGISTRY_BEAN_NAME)
	public RabbitListenerEndpointRegistry defaultRabbitListenerEndpointRegistry() {
		return new RabbitListenerEndpointRegistry();
	}

}

可以看到，其向IOC容器注入了bean后置处理器RabbitListenerAnnotationBeanPostProcessor，同时也注入了一个默认的RabbitListenerEndpointRegistry。

二、RabbitListenerAnnotationBeanPostProcessor

RabbitListenerAnnotationBeanPostProcessor类实现了BeanPostProcessor, Ordered, BeanFactoryAware, BeanClassLoaderAware, EnvironmentAware, SmartInitializingSingleton接口，Ordered表示处理顺序，BeanFactoryAware, BeanClassLoaderAware, EnvironmentAware主要用于获取对应的BeanFactory,BeanClassLoader, Environment属性，我们主要关注从SmartInitializingSingleton和BeanPostProcessor继承的方法。

1. RabbitListenerAnnotationBeanProcessor#afterSingletonsInstantiated

public void afterSingletonsInstantiated() {
	this.registrar.setBeanFactory(this.beanFactory);

	if (this.beanFactory instanceof ListableBeanFactory) {
		Map<String, RabbitListenerConfigurer> instances =
				((ListableBeanFactory) this.beanFactory).getBeansOfType(RabbitListenerConfigurer.class);
		for (RabbitListenerConfigurer configurer : instances.values()) {
			configurer.configureRabbitListeners(this.registrar);
		}
	}

	if (this.registrar.getEndpointRegistry() == null) {
		if (this.endpointRegistry == null) {
			Assert.state(this.beanFactory != null,
					"BeanFactory must be set to find endpoint registry by bean name");
			this.endpointRegistry = this.beanFactory.getBean(
					RabbitListenerConfigUtils.RABBIT_LISTENER_ENDPOINT_REGISTRY_BEAN_NAME,
					RabbitListenerEndpointRegistry.class);
		}
		this.registrar.setEndpointRegistry(this.endpointRegistry);
	}

	if (this.containerFactoryBeanName != null) {
		this.registrar.setContainerFactoryBeanName(this.containerFactoryBeanName);
	}

	// Set the custom handler method factory once resolved by the configurer