Spring Boot系列十五 spring boot集成RabbitMQ 源码分析

旧城等待， 2022-05-28 20:59 412阅读 0赞

## 1. 概述 ##

在这篇文章[Spring Boot系列十三 Spring Boot集成RabbitMQ][Spring Boot_ Spring Boot_RabbitMQ]中，我们介绍了在Spring Boot如何使用RabbitMQ，本篇文章中，从源码中分析Spring Boot如何集成RabbitMQ。

## 2. 入口 ##

在spring-boot-autoconfigure.jar中的spring.factories中有如下定义，表示spring启动时，会执行RabbitAutoConfiguration的初始化

… 
    # Auto Configure
    org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
    org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
    …

## 3. RabbitProperties ##

application\_\*.yml属性文件

spring:
      # 配置rabbitMQspring:
      rabbitmq:
        host: 10.240.80.134
        username: spring-boot
        password: spring-boot
        virtual-host: spring-boot-vhost

以上的属性文件会被注入到RabbitProperties属性

@ConfigurationProperties(prefix = "spring.rabbitmq")
    public class RabbitProperties {
        …
    }

## 4. RabbitAutoConfiguration ##

### 4.1. 类上的注解分析： ###

这是一个配置类，在启动时会初始化上面提到RabbitProperties对象，然后它会引入另一个配置类RabbitAnnotationDrivenConfiguration，这个配置类和消息监听有关我们后面再介绍  
这个类有3个内部类，且都是配置类，这此配置类会根据条件初始RabbitMQ所需要的类

@Configuration
    @ConditionalOnClass({ RabbitTemplate.class, Channel.class }) 
    // 会初始化RabbitProperties.class
    @EnableConfigurationProperties(RabbitProperties.class) 
    // 引入@Configuration类RabbitAnnotationDrivenConfiguration
    @Import(RabbitAnnotationDrivenConfiguration.class)
    public class RabbitAutoConfiguration { 
    …
    
    }

### 4.2. 内部类RabbitConnectionFactoryCreator ###

内部类RabbitConnectionFactoryCreator会根据RabbitProperties 配置的参数初始CachingConnectionFactory 实例（它是ConnectionFactory 子类），这个实例是连接RabbitMQ的连接池。  
CachingConnectionFactory实例是对RabbitMQ官方提供对com.rabbitmq.client.ConnectionFactory和com.rabbitmq.client.Channel的封装，缓存这两种资源。CachingConnectionFactory有两种缓存模式  
1. 如果选择CacheMode\#CHANNEL的缓存模式，当我们调用 createConnection()方法时，每次返回相同的Connection。默认情况下，只创建一个Connection，只创建一个Channel（通过配置创建Channel数量参数，可以创建缓存多个Channel）。即可以创建多个Channel，但是所有的Channel共用同一个Connection  
2. 如果选择CacheMode\#CONNECTION的缓存模式，可以同时配置创建Connection的数量和Channel数据。当调用 createConnection()时，从缓存中获取可用Connection，如果没有且创建的数量没有达到上限，则创建新的Connection。同理Channel

@Configuration
    @ConditionalOnMissingBean(ConnectionFactory.class)
    protected static class RabbitConnectionFactoryCreator { 
    
        @Bean
        public CachingConnectionFactory rabbitConnectionFactory(RabbitProperties config)
            throws Exception {
            // 根据RabbitProperties 配置RabbitMQ的连接工厂类
            RabbitConnectionFactoryBean factory = new RabbitConnectionFactoryBean();
            if (config.determineHost() != null) {
                factory.setHost(config.determineHost());
            }
            …
            factory.afterPropertiesSet();
            // 连接缓存类
            CachingConnectionFactory connectionFactory = new CachingConnectionFactory(
                factory.getObject());
            connectionFactory.setAddresses(config.determineAddresses());
            connectionFactory.setPublisherConfirms(config.isPublisherConfirms());
            connectionFactory.setPublisherReturns(config.isPublisherReturns());
            …
            return connectionFactory;
        }
    
    }

### 4.3. 内部类RabbitTemplateConfiguration ###

内部类RabbitTemplateConfiguration通过类的构造器将RabbitProperties 配置的参数、MessageConverter赋值到类的相应的成员变量上，然后在方法rabbitTemplate()根据RabbitConnectionFactoryCreator创建的CachingConnectionFactory实例 ，创建出RabbitTemplate和RabbitAdmin。

@Configuration
    // 引入RabbitConnectionFactoryCreator
    @Import(RabbitConnectionFactoryCreator.class)
    protected static class RabbitTemplateConfiguration { 
        private final ObjectProvider<MessageConverter> messageConverter;
        private final RabbitProperties properties;
    
        // 注入MessageConverter和RabbitProperties 
        public RabbitTemplateConfiguration(
            ObjectProvider<MessageConverter> messageConverter,
            RabbitProperties properties) {
            this.messageConverter = messageConverter;
            this.properties = properties;
        }
    
        // 初始化RabbitTemplate 
        @Bean
        @ConditionalOnSingleCandidate(ConnectionFactory.class)
        @ConditionalOnMissingBean(RabbitTemplate.class)
        public RabbitTemplate rabbitTemplate(ConnectionFactory connectionFactory) {
            // 创建RabbitTemplate 
            RabbitTemplate rabbitTemplate = new RabbitTemplate(connectionFactory);
            MessageConverter messageConverter = this.messageConverter.getIfUnique();
            if (messageConverter != null) {
                // 配置MessageConverter 
                rabbitTemplate.setMessageConverter(messageConverter);
            }
            // 其它参数配置略
            …
            return rabbitTemplate;
        }
    
        // 初始化AmqpAdmin 
        @Bean
        @ConditionalOnSingleCandidate(ConnectionFactory.class)
        @ConditionalOnProperty(prefix = "spring.rabbitmq", name = "dynamic", matchIfMissing = true)
        @ConditionalOnMissingBean(AmqpAdmin.class)
        public AmqpAdmin amqpAdmin(ConnectionFactory connectionFactory) {
            // 创建RabbitAdmin
            return new RabbitAdmin(connectionFactory);
        }
    
    }

### 4.4. 内部配置类：MessagingTemplateConfiguration ###

内部配置类：MessagingTemplateConfiguration  
通过rabbitMessagingTemplate()方法将上面创建的RabbitTemplate 实例注入并创建RabbitMessagingTempla

@Configuration
    @ConditionalOnClass(RabbitMessagingTemplate.class)
    @ConditionalOnMissingBean(RabbitMessagingTemplate.class)
    // 引入RabbitTemplateConfiguration配置类 
    @Import(RabbitTemplateConfiguration.class)
    protected static class MessagingTemplateConfiguration { 
        // 生成实例RabbitMessagingTemplate， 其中RabbitTemplate 由RabbitTemplateConfiguration实例化
        @Bean
        @ConditionalOnSingleCandidate(RabbitTemplate.class)
        public RabbitMessagingTemplate rabbitMessagingTemplate(
        RabbitTemplate rabbitTemplate) {
            return new RabbitMessagingTemplate(rabbitTemplate);
        }
    
    }

通过以上配置就完成的RabbitMQ发送者相关的bean初始化，我们可以使用RabbitTemplate和RabbitAdmin发送消息。如果要监听RabbitMQ消息还需要如下配置，这个配置更加更复杂

## 5. RabbitAnnotationDrivenConfiguration ##

此类RabbitAutoConfiguration中引入此类，此类会创建监听消息相关的Bean。我们来详细分析这个类。

### 5.1. 类的构造方法 : ###

传入监控需要MessageConverter实例、MessageRecoverer实例、RabbitProperties 实例，做为的类的成员变量

@Configuration
    @ConditionalOnClass(EnableRabbit.class)
    class RabbitAnnotationDrivenConfiguration {
    
        private final ObjectProvider<MessageConverter> messageConverter;
    
        private final ObjectProvider<MessageRecoverer> messageRecoverer;
    
        private final RabbitProperties properties;
    
        RabbitAnnotationDrivenConfiguration(ObjectProvider<MessageConverter> messageConverter,
            ObjectProvider<MessageRecoverer> messageRecoverer,
            RabbitProperties properties) {
            this.messageConverter = messageConverter;
            this.messageRecoverer = messageRecoverer;
            this.properties = properties;
        }
        …
    }

### 5.2. 类的rabbitListenerContainerFactoryConfigurer()方法 ###

创建SimpleRabbitListenerContainerFactoryConfigurer 对象，此类保存创建RabbitListenerContainer所需要的MessageConverter实例、MessageRecoverer实例、RabbitProperties 实例

// 实例SimpleRabbitListenerContainerFactoryConfigurer 对象，设置MessageConverter、MessageRecovere、RabbitMQ的属性
    @Bean
    @ConditionalOnMissingBean
    public SimpleRabbitListenerContainerFactoryConfigurer rabbitListenerContainerFactoryConfigurer() {
        SimpleRabbitListenerContainerFactoryConfigurer configurer = new SimpleRabbitListenerContainerFactoryConfigurer();
        configurer.setMessageConverter(this.messageConverter.getIfUnique());
        configurer.setMessageRecoverer(this.messageRecoverer.getIfUnique());
        configurer.setRabbitProperties(this.properties);
        return configurer;
    }

### 5.3. 类中rabbitListenerContainerFactory()方法 ###

创建实例SimpleRabbitListenerContainerFactory （是RabbitListenerContainerFactory的子类），其中SimpleRabbitListenerContainerFactoryConfigurer 来自下面的方法，ConnectionFactory 来自RabbitAutoConfiguration，上面已经解释过了

@Bean
    @ConditionalOnMissingBean(name = "rabbitListenerContainerFactory")
    public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory(
        SimpleRabbitListenerContainerFactoryConfigurer configurer,
        ConnectionFactory connectionFactory) {
        SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
        configurer.configure(factory, connectionFactory);
        return factory;
    }

### 5.4. 启动@EnableRabbit ###

这个内部类主要看他的@EnableRabbit注解，这个注解会使用RabbitListenerContainer参数，并创建其他相关的Bean实例，并进行监听消息。下节详细介绍@EnableRabbit

@EnableRabbit
    @ConditionalOnMissingBean(name = RabbitListenerConfigUtils.RABBIT_LISTENER_ANNOTATION_PROCESSOR_BEAN_NAME)
    protected static class EnableRabbitConfiguration { 
    
    }

## 6. @EnableRabbit ##

引入配置类RabbitBootstrapConfiguration

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    // 引入配置类RabbitBootstrapConfiguration
    @Import(RabbitBootstrapConfiguration.class)
    public @interface EnableRabbit { 
    }

## 7. RabbitBootstrapConfiguration ##

在这个配置类创建RabbitListenerAnnotationBeanPostProcessor和RabbitListenerEndpointRegistry。

@Configuration
    public class RabbitBootstrapConfiguration { 
    
        // 创建RabbitListenerAnnotationBeanPostProcessor ，@RabbitListener+@RabbitHandler注解的方法，当收到监听消息分发到这些方法进行处理
        @Bean(name = RabbitListenerConfigUtils.RABBIT_LISTENER_ANNOTATION_PROCESSOR_BEAN_NAME)
        @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
        public RabbitListenerAnnotationBeanPostProcessor rabbitListenerAnnotationProcessor() {
            return new RabbitListenerAnnotationBeanPostProcessor();
        }
    
        // 创建RabbitListenerEndpointRegistry，供监听节点的注册 
        @Bean(name = RabbitListenerConfigUtils.RABBIT_LISTENER_ENDPOINT_REGISTRY_BEAN_NAME)
        public RabbitListenerEndpointRegistry defaultRabbitListenerEndpointRegistry() {
            return new RabbitListenerEndpointRegistry();
        }
    
    }

## 8. RabbitListenerAnnotationBeanPostProcessor ##

继承BeanPostProcessor，在Spring创建对象后，会拦截所有的被@RabbitListener+@RabbitHandler注解的方法

### 8.1. 类的afterSingletonsInstantiated()方法 ###

类在实例化时，会执行初始化，重要操作  
1. 设置获取RabbitListenerEndpointRegistry实例，并设置实例到RabbitListenerEndpointRegistrar中  
2. 在RabbitListenerEndpointRegistrar中设置containerFactoryBeanName名称为rabbitListenerContainerFactory  
3. 调用RabbitListenerEndpointRegistrar.afterPropertiesSet()进行初始化，这个方法内容后面再介绍

// 创建实例
    private final RabbitListenerEndpointRegistrar registrar = new RabbitListenerEndpointRegistrar();
    
    @Override
    public void afterSingletonsInstantiated() {
        …
    
        // 设置获取RabbitListenerEndpointRegistry实例，并设置实例到RabbitListenerEndpointRegistrar中
        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);
        }
    
        // 在RabbitListenerEndpointRegistrar中设置containerFactoryBeanName名称为rabbitListenerContainerFactory
        if (this.containerFactoryBeanName != null) {
            this.registrar.setContainerFactoryBeanName(this.containerFactoryBeanName);
        }
    
        // Set the custom handler method factory once resolved by the configurer
        MessageHandlerMethodFactory handlerMethodFactory = this.registrar.getMessageHandlerMethodFactory();
        if (handlerMethodFactory != null) {
            this.messageHandlerMethodFactory.setMessageHandlerMethodFactory(handlerMethodFactory);
        }
    
        // Actually register all listeners，初始化RabbitListenerEndpointRegistrar
        this.registrar.afterPropertiesSet();
    
    }

### 8.2. postProcessAfterInitialization()方法 ###

postProcessAfterInitialization()方法会在对象初始化完毕后被执行，此方法会拦截所有的被@RabbitListener和@RabbitHandler注解的方法。  
1. @RabbitListener如果注解到方法上，则调用方法processAmqpListener()，此时会使用MethodRabbitListenerEndpoint 封装调用方法  
2. @RabbitListener如果注解到类上，且类有方法被@RabbitHandler注解，则调用processMultiMethodListeners()，此时会使用MultiMethodRabbitListenerEndpoint 封装调用方法

MethodRabbitListenerEndpoint 和MultiMethodRabbitListenerEndpoint都是MethodRabbitListenerEndpoint 的子类

![这里写图片描述][SouthEast]

@Override
    public Object postProcessAfterInitialization(final Object bean, final String beanName) throws BeansException {
        …
        // 处理所有被@RabbitListener注解的方法 
        for (ListenerMethod lm : metadata.listenerMethods) {
            for (RabbitListener rabbitListener : lm.annotations) {
                processAmqpListener(rabbitListener, lm.method, bean, beanName);
            }
        }
    
        // 处理所有被@RabbitHandler注解的方法 
        if (metadata.handlerMethods.length > 0) {
            processMultiMethodListeners(metadata.classAnnotations, metadata.handlerMethods, bean, beanName);
        }
        return bean;
    }
    
    private void processMultiMethodListeners(RabbitListener[] classLevelListeners, Method[] multiMethods,
        Object bean, String beanName) {
        …
        for (RabbitListener classLevelListener : classLevelListeners) {
            // 创建处理有多个监听方法的类
            MultiMethodRabbitListenerEndpoint endpoint = new MultiMethodRabbitListenerEndpoint(checkedMethods, bean);
            endpoint.setBeanFactory(this.beanFactory);
            processListener(endpoint, classLevelListener, bean, bean.getClass(), beanName);
        }
    }
    
    protected void processAmqpListener(RabbitListener rabbitListener, Method method, Object bean, String beanName) {
        Method methodToUse = checkProxy(method, bean);
        // 创建处理单个监听方法的类
        MethodRabbitListenerEndpoint endpoint = new MethodRabbitListenerEndpoint();
        endpoint.setMethod(methodToUse);
        endpoint.setBeanFactory(this.beanFactory);
        processListener(endpoint, rabbitListener, bean, methodToUse, beanName);
    }

### 8.3. 方法processListener() ###

无论是方法processMultiMethodListeners()和processMultiMethodListeners()都会进入processListener()，这里做如下内容：  
1. 第一步这里先根据监听方法上的@RabbitListener的配置参数，设置MethodRabbitListenerEndpoint 要监听的队列、优先级、排他性等待，  
2. 第二步获取rabbitAdmin实例，并设置到MethodRabbitListenerEndpoint 中  
3. 第三步 根据@RabbitListener的containerFactory()配置的值获取RabbitListenerContainerFactory，默认值为空  
4. 第四步将调用工具类RabbitListenerEndpointRegistrar将RabbitListenerEndpoint注册到RabbitListenerEndpointRegistry。后面会解释这个RabbitListenerEndpointRegistrar类

protected void processListener(MethodRabbitListenerEndpoint endpoint, RabbitListener rabbitListener, Object bean,
        Object adminTarget, String beanName) {
    
        // 这里有设置MethodRabbitListenerEndpoint endpoint的要监听的队列、优先级、排他性等待
        …
    
        // 获取rabbitAdmin实例，并设置到MethodRabbitListenerEndpoint 中 
        String rabbitAdmin = resolve(rabbitListener.admin());
        if (StringUtils.hasText(rabbitAdmin)) {
            Assert.state(this.beanFactory != null, "BeanFactory must be set to resolve RabbitAdmin by bean name");
            try {
                endpoint.setAdmin(this.beanFactory.getBean(rabbitAdmin, RabbitAdmin.class));
            }
            catch (NoSuchBeanDefinitionException ex) {
                throw new BeanInitializationException("Could not register rabbit listener endpoint on [" +
                    adminTarget + "], no " + RabbitAdmin.class.getSimpleName() + " with id '" +
                    rabbitAdmin + "' was found in the application context", ex);
            }
        }
    
        // 根据@RabbitListener的containerFactory()配置的值获取RabbitListenerContainerFactory
        RabbitListenerContainerFactory<?> factory = null;
        String containerFactoryBeanName = resolve(rabbitListener.containerFactory());
        if (StringUtils.hasText(containerFactoryBeanName)) {
            Assert.state(this.beanFactory != null, "BeanFactory must be set to obtain container factory by bean name");
            try {
                factory = this.beanFactory.getBean(containerFactoryBeanName, RabbitListenerContainerFactory.class);
            }
            catch (NoSuchBeanDefinitionException ex) {
                throw new BeanInitializationException("Could not register rabbit listener endpoint on [" +
                    adminTarget + "] for bean " + beanName + ", no " +
                    RabbitListenerContainerFactory.class.getSimpleName() + " with id '" +
                    containerFactoryBeanName + "' was found in the application context", ex);
            }
        }
    
        // 调用工具类RabbitListenerEndpointRegistrar将RabbitListenerEndpoint注册到RabbitListenerEndpointRegistry。RabbitListenerEndpointRegistra下面会解释这个类
        this.registrar.registerEndpoint(endpoint, factory);
    }

## 9. RabbitListenerEndpointRegistrar ##

将上文的RabbitListenerEndpoint注册到RabbitListenerEndpointRegistry上的工作类

### 9.1. 初始化操作afterPropertiesSet() ###

初始化操作，此方法被RabbitListenerAnnotationBeanPostProcessor的afterSingletonsInstantiated()方法调用，触发初始化 。主要内容如下：

1.  第一步：循环AmqpListenerEndpointDescriptor，将MethodRabbitListenerEndpoint 和 RabbitListenerContainerFactory实例调用RabbitListenerEndpointRegistry的方法注册到此类上
2.  第二步：设置startImmediately 为true，表示后面将

private RabbitListenerEndpointRegistry endpointRegistry;...
    
    // 初始化操作
    @Override
    public void afterPropertiesSet() {
        registerAllEndpoints();
    }
    
    protected void registerAllEndpoints() {
        synchronized (this.endpointDescriptors) {、
            # AmqpListenerEndpointDescriptor是保存RabbitListenerEndpoint和RabbitListenerContainerFactory实例
            for (AmqpListenerEndpointDescriptor descriptor : this.endpointDescriptors) {
                # 将MethodRabbitListenerEndpoint endpoint + RabbitListenerContainerFactory注册到endpointRegistry上
                this.endpointRegistry.registerListenerContainer(
                    descriptor.endpoint, resolveContainerFactory(descriptor));
            }
            # 设置值为true
            this.startImmediately = true;  // trigger immediate startup
        }
    }
    
    # 获取RabbitListenerContainerFactory实例
    /** 如果endpoint 结点注册是有RabbitListenerContainerFactory，则使用这个值（实际来自@RabbitListener的containerFactory()值）。 如果没有则使用默认的RabbitListenerContainerFactory，如果没有，则从spring容器中获取名称为containerFactoryBeanName值的RabbitListenerContainerFactory对象并设置为默认值 在之前我们已经知道这个值被RabbitListenerAnnotationBeanPostProcessor在afterSingletonsInstantiated()中设置为rabbitListenerContainerFactory **/
    private RabbitListenerContainerFactory<?> resolveContainerFactory(AmqpListenerEndpointDescriptor descriptor) {
        if (descriptor.containerFactory != null) {
            return descriptor.containerFactory;
        }
        else if (this.containerFactory != null) {
            return this.containerFactory;
        }
        else if (this.containerFactoryBeanName != null) {
            Assert.state(this.beanFactory != null, "BeanFactory must be set to obtain container factory by bean name");
            this.containerFactory = this.beanFactory.getBean(
                this.containerFactoryBeanName, RabbitListenerContainerFactory.class);
            return this.containerFactory;  // Consider changing this if live change of the factory is required
        }
        else {
            throw new IllegalStateException("Could not resolve the " +
                RabbitListenerContainerFactory.class.getSimpleName() + " to use for [" +
                descriptor.endpoint + "] no factory was given and no default is set.");
        }
    }

### 9.2. registerEndpoint()方法 ###

此方法被RabbitListenerAnnotationBeanPostProcessor的processListener()方法调用。主要内容如下：  
在之前的分析中我们初始化设置startImmediately=true，现在只分析true情况。此时调用 RabbitListenerEndpointRegistry的registerListenerContainer()方法将且传递参数startImmediately=true

// 在 RabbitListenerAnnotationBeanPostProcessor调用此方法进行注册
    
    private RabbitListenerEndpointRegistry endpointRegistry;
    
    public void registerEndpoint(RabbitListenerEndpoint endpoint, RabbitListenerContainerFactory<?> factory) {
        …
        // Factory may be null, we defer the resolution right before actually creating the container
        AmqpListenerEndpointDescriptor descriptor = new AmqpListenerEndpointDescriptor(endpoint, factory);
        synchronized (this.endpointDescriptors) {
            if (this.startImmediately) { // Register and start immediately
                # 在之前的分析中我们发现startImmediately=true，现在只分析true情况
                # 调用endpointRegistry的方法注册到上面this.endpointRegistry.registerListenerContainer(descriptor.endpoint,
                    resolveContainerFactory(descriptor), true);
            }
            else {
                this.endpointDescriptors.add(descriptor);
            }
        }
    }

## 10. RabbitListenerEndpointRegistry ##

功能： 为已经注册的RabbitListenerEndpoint创建MessageListenerContainer实例，并执行MessageListenerContainer的初始化操作，最后执行此对象的start()方法。此类还管理监听容器的生命周期

### 10.1. registerListenerContainer()方法： ###

1.  第一步：为RabbitListenerEndpoint 根据RabbitListenerContainerFactory创建一个MessageListenerContainer监听器
2.  第二步：从上文知道我们startImmediately值为true，会执行startIfNecessary()启动MessageListenerContainer

// 设置RabbitListenerEndpoint 创建一个监听容器
    public void registerListenerContainer(RabbitListenerEndpoint endpoint, RabbitListenerContainerFactory<?> factory,
                                              boolean startImmediately) {
            Assert.notNull(endpoint, "Endpoint must not be null");
            Assert.notNull(factory, "Factory must not be null");
    
        String id = endpoint.getId();
        Assert.hasText(id, "Endpoint id must not be empty");
        synchronized (this.listenerContainers) {
            Assert.state(!this.listenerContainers.containsKey(id),
                "Another endpoint is already registered with id '" + id + "'");
            # 为endpoint根据factory创建一个监听器，方法详细见下边
            MessageListenerContainer container = createListenerContainer(endpoint, factory);
            this.listenerContainers.put(id, container);
            # Group？？
            if (StringUtils.hasText(endpoint.getGroup()) && this.applicationContext != null) {
                List<MessageListenerContainer> containerGroup;
                if (this.applicationContext.containsBean(endpoint.getGroup())) {
                    containerGroup = this.applicationContext.getBean(endpoint.getGroup(), List.class);
                }
                else {
                    containerGroup = new ArrayList<MessageListenerContainer>();
                    this.applicationContext.getBeanFactory().registerSingleton(endpoint.getGroup(), containerGroup);
                }
                containerGroup.add(container);
            }
            if (startImmediately) {
                # 启动容器MessageListenerContainer，已知传入的值为true
                startIfNecessary(container);
            }
        }
    }

### 10.2. createListenerContainer()方法 ###

1.  第一步： 使用RabbitListenerEndpoint 配置的RabbitListenerContainerFactory的方法createListenerContainer()创建MessageListenerContainer 。默认是使用SimpleRabbitListenerContainerFactory创建的实例为SimpleMessageListenerContainer
2.  第二步：因为MessageListenerContainer 继承InitializingBean，所有会执行SimpleMessageListenerContainer的初始化操作。后面会介绍这个类的初始化

# 为endpoint根据factory创建一个监听器
    protected MessageListenerContainer createListenerContainer(RabbitListenerEndpoint endpoint,
        RabbitListenerContainerFactory<?> factory) {
        # 使用endpoint配置的RabbitListenerContainerFactory创建MessageListenerContainer 。默认是使用SimpleRabbitListenerContainerFactory创建的实例为SimpleMessageListenerContainer
        MessageListenerContainer listenerContainer = factory.createListenerContainer(endpoint);
        # 初始化容器
        if (listenerContainer instanceof InitializingBean) {
            try {
                ((InitializingBean) listenerContainer).afterPropertiesSet();
            }
            catch (Exception ex) {
                throw new BeanInitializationException("Failed to initialize message listener container", ex);
            }
        }
        …
        return listenerContainer;
    }

### 10.3. 启动容器 ###

调用MessageListenerContainer 的start()方法启动容器

// 启动容器 
    private void startIfNecessary(MessageListenerContainer listenerContainer) {
        if (this.contextRefreshed || listenerContainer.isAutoStartup()) {
            // 容器默认值为自动启动，所有会执行一下操作
            listenerContainer.start();
        }
    }

## 11. 类SimpleRabbitListenerContainerFactory ##

此类是RabbitListenerContainerFactory的子类

### 11.1. createContainerInstance() 方法 ###

创建SimpleMessageListenerContainer实例

// 创建SimpleMessageListenerContainer实例 
    @Override
    protected SimpleMessageListenerContainer createContainerInstance() {
        return new SimpleMessageListenerContainer();
    }

### 11.2. 方法createContainerInstance() ###

此方法：调用createContainerInstance()创建SimpleMessageListenerContainer实例，并使用RabbitListenerEndpoint包含的参数设置到创建的实例中，最后调用initializeContainer()初始化SimpleMessageListenerContainer实例

@Override
    public C createListenerContainer(RabbitListenerEndpoint endpoint) {
        // 创建实例
        C instance = createContainerInstance();
    
        // 以下设置容器的初始值
        if (this.connectionFactory != null) {
            instance.setConnectionFactory(this.connectionFactory);
        }
        // 其他根据本对象的成员变量配置RabbitListenerEndpoint 代码略
        …
        instance.setListenerId(endpoint.getId());
    
        endpoint.setupListenerContainer(instance);
    
        // 初始化容器
        initializeContainer(instance);
    
        return instance;
    }

### 11.3. initializeContainer()方法 ###

初始化刚刚创建的SimpleMessageListenerContainer实例，将本对象中的成员变量配置到SimpleMessageListenerContainer实例中

// 根据容器工厂初始化容器值 
    @Override
    protected void initializeContainer(SimpleMessageListenerContainer instance) {
        super.initializeContainer(instance);
    
        if (this.applicationContext != null) {
            instance.setApplicationContext(this.applicationContext);
        }
        if (this.taskExecutor != null) {
            instance.setTaskExecutor(this.taskExecutor);
        }
        if (this.transactionManager != null) {
            instance.setTransactionManager(this.transactionManager);
        }
        if (this.txSize != null) {
            instance.setTxSize(this.txSize);
        }
        // 其他根据本对象的成员变量配置SimpleMessageListenerContainer 代码略
        …
    }

## 12. SimpleMessageListenerContainer ##

在RabbitListenerEndpointRegistry中会调用SimpleMessageListenerContainer的start()方法

### 12.1. start()方法 ###

如果没有初始化，则执行此类的初始化操作

// 初始操作，主要操作见doStart() 
    @Override
    public void start() {
        if (!this.initialized) {
            synchronized (this.lifecycleMonitor) {
                if (!this.initialized) {
                    afterPropertiesSet();
                    this.initialized = true;
                }
            }
        }
        try {
            if (logger.isDebugEnabled()) {
                logger.debug("Starting Rabbit listener container.");
            }
            # 调用子类方法
            doStart();
        }
        catch (Exception ex) {
            throw convertRabbitAccessException(ex);
        }
    }

### 12.2. doStart()方法： ###

主要操作如下：  
第一步：获取RabbitAdmin实例  
第二步：rabbitAdmin初始化：对新增的队列、交换机、绑定在RabbitMQ上进行声明  
第三步：调用父类doStart()方法  
第四步：在线程池中启动这个消息者，进行消息消费  
第五步：监控消息者是否启动成功，如果失败则抛出异常

protected void doStart() throws Exception {
        if (getMessageListener() instanceof ListenerContainerAware) {
            // 验证当前监听的队列是否和容器相同 
            ….
            Collection<String> expectedQueueNames = ((ListenerContainerAware) getMessageListener()).expectedQueueNames();
            if (expectedQueueNames != null) {
                String[] queueNames = getQueueNames();
                Assert.state(expectedQueueNames.size() == queueNames.length,
                    "Listener expects us to be listening on '" + expectedQueueNames + "'; our queues: "
                        + Arrays.asList(queueNames));
                boolean found = false;
                for (String queueName : queueNames) {
                    if (expectedQueueNames.contains(queueName)) {
                        found = true;
                    }
                    else {
                        found = false;
                        break;
                    }
                }
                Assert.state(found, "Listener expects us to be listening on '" + expectedQueueNames + "'; our queues: "
                    + Arrays.asList(queueNames));
            }
        }
        // 获取rabbitAdmin值
        if (this.rabbitAdmin == null && this.getApplicationContext() != null) {
            Map<String, RabbitAdmin> admins = this.getApplicationContext().getBeansOfType(RabbitAdmin.class);
            if (admins.size() == 1) {
                this.rabbitAdmin = admins.values().iterator().next();
            }
            else {
                ….
            }
        }
        // rabbitAdmin初始化：对新增的队列、交换机、绑定在RabbitMQ上进行声明 
        checkMismatchedQueues();
        // 调用父类方法
        super.doStart();
        synchronized (this.consumersMonitor) {
            // 初始化消息者，此方法会创建消息者BlockingQueueConsumer
            int newConsumers = initializeConsumers();
            ….
            Set<AsyncMessageProcessingConsumer> processors = new HashSet<AsyncMessageProcessingConsumer>();
            // 在线程池中启动这个消息者，进行消息消费：AsyncMessageProcessingConsumer 是个线程类，它调用BlockingQueueConsumer的start()方法接收消息并进行处理。
            for (BlockingQueueConsumer consumer : this.consumers) {
                AsyncMessageProcessingConsumer processor = new AsyncMessageProcessingConsumer(consumer);
                processors.add(processor);
                // 在线程池中执行 AsyncMessageProcessingConsumer 
                this.taskExecutor.execute(processor);
                if (this.applicationEventPublisher != null) {
                    this.applicationEventPublisher.publishEvent(new AsyncConsumerStartedEvent(this, consumer));
                }
            }
            // 监控消息者是否启动成功，如果失败则抛出异常
            for (AsyncMessageProcessingConsumer processor : processors) {
                FatalListenerStartupException startupException = processor.getStartupException();
                if (startupException != null) {
                    throw new AmqpIllegalStateException("Fatal exception on listener startup", startupException);
                }
            }
        }
    }

## 13. RabbitAdmin： ##

rabbitAdmin初始化：对新增的队列、交换机、绑定在RabbitMQ上进行声明

public void initialize() {
    
        …
        // 获取所有的队列、交换机、绑定
        Collection<Exchange> contextExchanges = new LinkedList<Exchange>(
            this.applicationContext.getBeansOfType(Exchange.class).values());
        Collection<Queue> contextQueues = new LinkedList<Queue>(
            this.applicationContext.getBeansOfType(Queue.class).values());
        Collection<Binding> contextBindings = new LinkedList<Binding>(
            this.applicationContext.getBeansOfType(Binding.class).values());
    
        … 
        // 在RabbitMQ上进行声明，创建对应的队列、交换机、绑定
        this.rabbitTemplate.execute(new ChannelCallback<Object>() {
            @Override
            public Object doInRabbit(Channel channel) throws Exception {
                declareExchanges(channel, exchanges.toArray(new Exchange[exchanges.size()]));
                declareQueues(channel, queues.toArray(new Queue[queues.size()]));
                declareBindings(channel, bindings.toArray(new Binding[bindings.size()]));
                return null;
            }
        });
    
    
        }

## 14. AsyncMessageProcessingConsumer ##

继承Runnable，的run()方法中调用BlockingQueueConsumer 的start()方法

private final class AsyncMessageProcessingConsumer implements Runnable { 
    
        private final BlockingQueueConsumer consumer;
    
        private volatile FatalListenerStartupException startupException;
    
        private AsyncMessageProcessingConsumer(BlockingQueueConsumer consumer) {
            this.consumer = consumer;
            this.start = new CountDownLatch(1);
        }
    
        @Override
        public void run() {
    
        ….
        try {
            if (SimpleMessageListenerContainer.this.autoDeclare) {
            SimpleMessageListenerContainer.this.redeclareElementsIfNecessary();
            }
            // 启动BlockingQueueConsumer 的start()方法
            this.consumer.start();
            ..
        }
        …
    ...

## 15. BlockingQueueConsumer ##

BlockingQueueConsumer：在start中调用basicConsume方法定阅消息。在这里我们可以看到spring开始调用RabbitMQ提供的Jar包里的类(.channel.basicConsume)，说明我们已经跟到底层，所有源码分析到此为止

### 15.1. 线程start()方法 ###

void start() throws AmqpException {
    
            try {
                    for (String queueName : this.queues) {
                            // 循环订阅所有的消息
                            if (!this.missingQueues.contains(queupublic eName)) {
                                    consumeFromQueue(queueName);
                            }
                    }
                    }
                    catch (IOException e) {
                            throw RabbitExceptionTranslator.convertRabbitAccessException(e);
                    }
                    }
    
                    private void consumeFromQueue(String queue) throws IOException {
                            // 调用basicConsume方法定阅消息。在这里我们可以看到spring开始调用RabbitMQ提供的Jar包里的类(.channel.basicConsume)，
                            String consumerTag = this.channel.basicConsume(queue, this.acknowledgeMode.isAutoAck(),
                                    (this.tagStrategy != null ? this.tagStrategy.createConsumerTag(queue) : ""), false, this.exclusive,
                                    this.consumerArgs, this.consumer);
                            if (consumerTag != null) {
                                    this.consumerTags.put(consumerTag, queue);
                            }
                            ...
                    }
    
            }

[Spring Boot_ Spring Boot_RabbitMQ]: http://blog.csdn.net/hry2015/article/details/79545157
[SouthEast]: /images/20220529/08571fc82d25400dab86009d2fa9f335.png