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这篇文章主要讲解了“@RabbitListener起作用的原理是什么”,文中的讲解内容简单清晰,易于学习与理解,下面请大家跟着小编的思路慢慢深入,一起来研究和学习“@RabbitListener起作用的原理是什么”吧!
在spring中,定义rabbitMq的消费者可以相当方便,只需要在消息处理类或者类方法加上@RabbitListener注解,指定队列名称即可。
如下代码:
@Component public class RabbitMqListener1 { @RabbitListener(queues = "queue1") public void consumer1(Message message) { } @RabbitListener(queues = "queue2") public void consumer2(String messsageBody) { } } @Component @RabbitListener(queues = "queue3") public class RabbitMqListener2 { @RabbitHandler(isDefault=true) public void consumer3() { } }
注意!!!如果@RabbitListener加在类上面,需要有一个默认的处理方法@RabbitHandler(isDefault=true),默认是false。
不设置一个true,消费mq消息的时候会出现“Listener method ‘no match’ threw exception”异常。
原因在RabbitListenerAnnotationBeanPostProcessor.processMultiMethodListeners方法,有兴趣的可以看下。
可以看到代码相当的简单。但是!!!为什么加上这个注解,就能作为一个consumer接受mq的消息呢?为啥处理mq消息的方法,入参可以那么随意?
有经验的程序员,可能会有这样的设想:
1、单纯看这些listener的代码,只是定义了由spring管理的bean,要能监听rabbitMq的消息,肯定需要有另外一个类,这个类会扫描所有加了@RabbitListener的bean,进行加工。
2、看这些listener的代码,可以发现处理mq消息的,都是具体的某个方法。那加工的过程,应该就是利用反射拿到对象、方法和@RabbitListener中的queue属性,然后建立一个绑定关系(对象+方法)——>(queue的consumer)。queue的consumer在接收到mq消息后,找到绑定的“对象+方法”,再通过反射的方式,调用真正的处理方法。
3、mq消息的处理方法,可以那么随意,应该是queue的consumer在调用真正处理方法之前,需要根据处理方法的参数类型,做一次数据转换。
接下来,就去看看源码,看一下设想是不是正确的~~
1、谁来扫描@RabbitListener注解的bean
在springBoot使用rabbit,一般是在@Configuration类上加上@EnableRabbit注解来开启rabbit功能。那我们就去看看@EnableRabbit注解的源码,看这个注解的作用
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Import(RabbitBootstrapConfiguration.class) public @interface EnableRabbit { }
可以看到,这个注解的作用,是导入RabbitBootstrapConfiguration配置类
@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(); } }
RabbitBootstrapConfiguration 配置类的作用,就是定义了RabbitListenerAnnotationBeanPostProcessor 和RabbitListenerEndpointRegistry 两个bean。
看到RabbitListenerAnnotationBeanPostProcessor 这个类名,就可以猜到,该类的实例bean就是用来扫描加了@RabbitListener 的类,并做一些加工。
(“RabbitListenerAnnotationBean”——针对添加了@RabbitListener注解的bean; “PostProcessor”——后置加工)
2、怎么建立(对象+方法)——>(queue的consumer)的映射关系
分析一下RabbitListenerAnnotationBeanPostProcessor类的源码
// 实现了BeanPostProcessor、Ordered、BeanFactoryAware、BeanClassLoaderAware、EnvironmentAware和SmartInitializingSingleton 6个接口 public class RabbitListenerAnnotationBeanPostProcessor implements BeanPostProcessor, Ordered, BeanFactoryAware, BeanClassLoaderAware, EnvironmentAware, SmartInitializingSingleton { ....... // 完成初始化bean之后,调用该方法 @Override public Object postProcessAfterInitialization(final Object bean, final String beanName) throws BeansException { Class<?> targetClass = AopUtils.getTargetClass(bean); TypeMetadata metadata = this.typeCache.get(targetClass); if (metadata == null) { metadata = buildMetadata(targetClass); this.typeCache.putIfAbsent(targetClass, metadata); } for (ListenerMethod lm : metadata.listenerMethods) { for (RabbitListener rabbitListener : lm.annotations) { processAmqpListener(rabbitListener, lm.method, bean, beanName); } } if (metadata.handlerMethods.length > 0) { processMultiMethodListeners(metadata.classAnnotations, metadata.handlerMethods, bean, beanName); } return bean; } // 根据Class,获取元数据 private TypeMetadata buildMetadata(Class<?> targetClass) { Collection<RabbitListener> classLevelListeners = findListenerAnnotations(targetClass); final boolean hasClassLevelListeners = classLevelListeners.size() > 0; final List<ListenerMethod> methods = new ArrayList<ListenerMethod>(); final List<Method> multiMethods = new ArrayList<Method>(); ReflectionUtils.doWithMethods(targetClass, new ReflectionUtils.MethodCallback() { @Override public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException { Collection<RabbitListener> listenerAnnotations = findListenerAnnotations(method); if (listenerAnnotations.size() > 0) { methods.add(new ListenerMethod(method, listenerAnnotations.toArray(new RabbitListener[listenerAnnotations.size()]))); } if (hasClassLevelListeners) { RabbitHandler rabbitHandler = AnnotationUtils.findAnnotation(method, RabbitHandler.class); if (rabbitHandler != null) { multiMethods.add(method); } } } }, ReflectionUtils.USER_DECLARED_METHODS); if (methods.isEmpty() && multiMethods.isEmpty()) { return TypeMetadata.EMPTY; } return new TypeMetadata( methods.toArray(new ListenerMethod[methods.size()]), multiMethods.toArray(new Method[multiMethods.size()]), classLevelListeners.toArray(new RabbitListener[classLevelListeners.size()])); } // 检查一下是否使用jdk代理,使用jdk代理方式必须实现了接口 // new一个MethodRabbitListenerEndpoint对象,交由processListener方法进行处理 protected void processAmqpListener(RabbitListener rabbitListener, Method method, Object bean, String beanName) { Method methodToUse = checkProxy(method, bean); MethodRabbitListenerEndpoint endpoint = new MethodRabbitListenerEndpoint(); endpoint.setMethod(methodToUse); endpoint.setBeanFactory(this.beanFactory); processListener(endpoint, rabbitListener, bean, methodToUse, beanName); } // 前面大半代码都是对MethodRabbitListenerEndpoint对象的属性设置:处理消息的bean、消息处理方法的工厂类、监听的队列名。。。。 // 通过beanFactory获取RabbitListenerContainerFactory类的bean // 调用RabbitListenerEndpointRegistar的registerEndpoint方法注册mq消息消费端点 protected void processListener(MethodRabbitListenerEndpoint endpoint, RabbitListener rabbitListener, Object bean, Object adminTarget, String beanName) { endpoint.setBean(bean); endpoint.setMessageHandlerMethodFactory(this.messageHandlerMethodFactory); endpoint.setId(getEndpointId(rabbitListener)); endpoint.setQueueNames(resolveQueues(rabbitListener)); String group = rabbitListener.group(); if (StringUtils.hasText(group)) { Object resolvedGroup = resolveExpression(group); if (resolvedGroup instanceof String) { endpoint.setGroup((String) resolvedGroup); } } endpoint.setExclusive(rabbitListener.exclusive()); String priority = resolve(rabbitListener.priority()); if (StringUtils.hasText(priority)) { try { endpoint.setPriority(Integer.valueOf(priority)); } catch (NumberFormatException ex) { throw new BeanInitializationException("Invalid priority value for " + rabbitListener + " (must be an integer)", ex); } } 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); } } 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); } } this.registrar.registerEndpoint(endpoint, factory); } ........ }
这个类的代码比较长,只贴部分比较主要的部分,其他的,可以自己查看源码进行了解。
RabbitListenerAnnotationBeanPostProcessor实现了BeanPostProcessor(bean初始化后的后置处理)、Ordered(后置处理的排序)、BeanFactoryAware(注入BeanFactory)、BeanClassLoaderAware(注入BeanClassLoader)、EnvironmentAware(注入spring环境)和SmartInitializingSingleton(单例bean初始化后的回调) 6个接口。
我们需要关注的是BeanPostProcessor接口定义的方法,看postProcessAfterInitialization方法的代码,大致流程为:
1、通过AopUtils得到bean代理的对象的class
2、判断缓存中是否有该class的类型元数据,如果没有则调用buildMetadata方法生成类型元数据并放入缓存
3、遍历加了@RabbitListener注解的方法,调用processAmqpListener方法进行处理
4、调用processMultiMethodListeners方法对加了@RabbitHandler的方法进行处理
关于buildMetadata方法:
代码不复杂,就是利用反射,拿到class中,添加了@RabbitListener和@RabbitHandler注解的方法。另外,从代码中也可以看出,@RabbitHandler注解要生效,必须在class上增加@RabbitListener注解
关于processAmqpListener方法:
没有什么实际内容,就干两个事情:
1、检查一下是否使用jdk代理,使用jdk代理方式必须实现了接口
2、new一个MethodRabbitListenerEndpoint对象,交由processListener方法进行处理
关于processListener方法:
1、前面大半代码都是对MethodRabbitListenerEndpoint对象的属性设置:处理消息的bean、消息处理方法的工厂类、监听的队列名。。。。
其中要关注一下setMessageHandlerMethodFactory方法,查看MessageHandlerMethodFactory接口的源码
public interface MessageHandlerMethodFactory { InvocableHandlerMethod createInvocableHandlerMethod(Object bean, Method method);
从入参和返回值可以看出来,这个工厂的作用就是将spring的bean对象和方法包装成一个InvocableHandlerMethod对象,也就是我们上面提到的(对象+方法)。
2、通过beanFactory获取RabbitListenerContainerFactory类的bean。
3、调用RabbitListenerEndpointRegistar的registerEndpoint方法注册mq消息消费端点。
继续往下追,看一下RabbitListenerEndpointRegistar的代码:
public class RabbitListenerEndpointRegistrar implements BeanFactoryAware, InitializingBean { // 将整个endpointDescriptors数组进行注册 protected void registerAllEndpoints() { synchronized (this.endpointDescriptors) { for (AmqpListenerEndpointDescriptor descriptor : this.endpointDescriptors) { this.endpointRegistry.registerListenerContainer( descriptor.endpoint, resolveContainerFactory(descriptor)); } this.startImmediately = true; // trigger immediate startup } } // 解析得到RabbitListenerContainerFactory // 如果AmqpListenerEndpointDescriptor 的containerFactory属性不为空,直接返回containerFactory // 如果为空,尝试从beanFactory获取 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."); } } // new一个AmqpListenerEndpointDescriptor对象 // 如果立即启动,则调用RabbitListenerEndpointRegistry注册器来注册消息监听 // 如果不是立即启动,则添加到endpointDescriptors列表中,后面通过registerAllEndpoints方法统一启动 public void registerEndpoint(RabbitListenerEndpoint endpoint, RabbitListenerContainerFactory<?> factory) { Assert.notNull(endpoint, "Endpoint must be set"); Assert.hasText(endpoint.getId(), "Endpoint id must be set"); // 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 this.endpointRegistry.registerListenerContainer(descriptor.endpoint, resolveContainerFactory(descriptor), true); } else { this.endpointDescriptors.add(descriptor); } } } }
从上面的代码可以看出,我们关心的内容,应该是在RabbitListenerEndpointRegistry类的registerListenerContainer方法!!
public class RabbitListenerEndpointRegistry implements DisposableBean, SmartLifecycle, ApplicationContextAware, ApplicationListener<ContextRefreshedEvent> { // 检查是否被注册过,注册过就不能注册第二次 // 调用createListenerContainer创建消息监听 // 关于分组消费的,我们不关心 // 是否立即启动,是的话,同步调用startIfNecessary方法 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 + "'"); MessageListenerContainer container = createListenerContainer(endpoint, factory); this.listenerContainers.put(id, container); 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) { startIfNecessary(container); } } // 其实就是调用了RabbitListenerContainerFactory的createListenerContainer生成了一个MessageListenerContainer对象 protected MessageListenerContainer createListenerContainer(RabbitListenerEndpoint endpoint, RabbitListenerContainerFactory<?> factory) { MessageListenerContainer listenerContainer = factory.createListenerContainer(endpoint); if (listenerContainer instanceof InitializingBean) { try { ((InitializingBean) listenerContainer).afterPropertiesSet(); } catch (Exception ex) { throw new BeanInitializationException("Failed to initialize message listener container", ex); } } int containerPhase = listenerContainer.getPhase(); if (containerPhase < Integer.MAX_VALUE) { // a custom phase value if (this.phase < Integer.MAX_VALUE && this.phase != containerPhase) { throw new IllegalStateException("Encountered phase mismatch between container factory definitions: " + this.phase + " vs " + containerPhase); } this.phase = listenerContainer.getPhase(); } return listenerContainer; } }
createListenerContainer方法调用了RabbitListenerContainerFactory接口的createListenerContainer方法创建一个MessageListenerContainer对象。
在这里,如果是通过RabbitAutoConfiguration自动配置的,那么RabbitListenerContainerFactory接口的具体实现类是SimpleRabbitListenerContainerFactory,MessageListenerContainer接口的具体实现类是SimpleMessageListenerContainer。有兴趣的话,可以去看下rabbitMq自动配置的几个类。
RabbitListenerContainerFactory接口的createListenerContainer方法是由AbstractRabbitListenerContainerFactory抽象类实现,代码如下:
@Override public C createListenerContainer(RabbitListenerEndpoint endpoint) { C instance = createContainerInstance(); if (this.connectionFactory != null) { instance.setConnectionFactory(this.connectionFactory); } if (this.errorHandler != null) { instance.setErrorHandler(this.errorHandler); } if (this.messageConverter != null) { instance.setMessageConverter(this.messageConverter); } if (this.acknowledgeMode != null) { instance.setAcknowledgeMode(this.acknowledgeMode); } if (this.channelTransacted != null) { instance.setChannelTransacted(this.channelTransacted); } if (this.autoStartup != null) { instance.setAutoStartup(this.autoStartup); } if (this.phase != null) { instance.setPhase(this.phase); } instance.setListenerId(endpoint.getId()); // 最重要的一行!!! endpoint.setupListenerContainer(instance); initializeContainer(instance); return instance; }
乍一看,都是对MessageListenerContainer实例的初始化,实际上有一行,相当重要“ endpoint.setupListenerContainer(instance); ”,这一行最终是走到
AbstractRabbitListenerEndpoint.setupListenerContainer
public abstract class AbstractRabbitListenerEndpoint implements RabbitListenerEndpoint, BeanFactoryAware { ...... // 设置MessageListenerContainer,最重要的就是设置监听的队列名称!!! @Override public void setupListenerContainer(MessageListenerContainer listenerContainer) { SimpleMessageListenerContainer container = (SimpleMessageListenerContainer) listenerContainer; boolean queuesEmpty = getQueues().isEmpty(); boolean queueNamesEmpty = getQueueNames().isEmpty(); if (!queuesEmpty && !queueNamesEmpty) { throw new IllegalStateException("Queues or queue names must be provided but not both for " + this); } if (queuesEmpty) { Collection<String> names = getQueueNames(); container.setQueueNames(names.toArray(new String[names.size()])); } else { Collection<Queue> instances = getQueues(); container.setQueues(instances.toArray(new Queue[instances.size()])); } container.setExclusive(isExclusive()); if (getPriority() != null) { Map<String, Object> args = new HashMap<String, Object>(); args.put("x-priority", getPriority()); container.setConsumerArguments(args); } if (getAdmin() != null) { container.setRabbitAdmin(getAdmin()); } setupMessageListener(listenerContainer); } // 创建MessageListener protected abstract MessageListener createMessageListener(MessageListenerContainer container); // 创建MessageListener,设置到MessageListenerContainer 里 private void setupMessageListener(MessageListenerContainer container) { MessageListener messageListener = createMessageListener(container); Assert.state(messageListener != null, "Endpoint [" + this + "] must provide a non null message listener"); container.setupMessageListener(messageListener); } ...... }
用@RabbitLinstener注解的方法,使用的endpoint是MethodRabbitListenerEndpoint继承自AbstractRabbitListenerEndpoint,所以看看AbstractRabbitListenerEndpoint的createMessageListener方法
public class MethodRabbitListenerEndpoint extends AbstractRabbitListenerEndpoint { ...... @Override protected MessagingMessageListenerAdapter createMessageListener(MessageListenerContainer container) { Assert.state(this.messageHandlerMethodFactory != null, "Could not create message listener - MessageHandlerMethodFactory not set"); MessagingMessageListenerAdapter messageListener = createMessageListenerInstance(); messageListener.setHandlerMethod(configureListenerAdapter(messageListener)); String replyToAddress = getDefaultReplyToAddress(); if (replyToAddress != null) { messageListener.setResponseAddress(replyToAddress); } MessageConverter messageConverter = container.getMessageConverter(); if (messageConverter != null) { messageListener.setMessageConverter(messageConverter); } if (getBeanResolver() != null) { messageListener.setBeanResolver(getBeanResolver()); } return messageListener; } protected MessagingMessageListenerAdapter createMessageListenerInstance() { return new MessagingMessageListenerAdapter(this.bean, this.method); } ...... }
从上面代码可以看出,createMessageListener方法返回了一个MessagingMessageListenerAdapter实例,MessagingMessageListenerAdapter实现了MessageListener接口
到这里,我们就能得出一些结论:
1、有@RabbitListener注解的方法,会生成MethodRabbitListenerEndpoint对象
2、通过MethodRabbitListenerEndpoint对象和SimpleRabbitListenerContainerFactory工厂bean,生成SimpleMessageListenerContainer对象
3、SimpleMessageListenerContainer对象保存了要监听的队列名,创建了用于处理消息的MessagingMessageListenerAdapter实例
4、MessagingMessageListenerAdapter持有@RabbitListener注解的对象和方法,起到一个适配器的作用
SimpleMessageListenerContainer是相当重要的一个类,,包装了整个mq消息消费需要的信息:
1、保存了要监听的队列名,启动的时候,根据队列名创建从服务器拉取消息的consumer——BlockingQueueConsumer
2、创建了一个MessagingMessageListenerAdapter对象,当consumer从服务器拿到消息后,由MessagingMessageListenerAdapter进行处理
3、谁来做数据转换?
是MessagingMessageListenerAdapter,有兴趣的,可以看看MessagingMessageListenerAdapter转换参数的源码。
感谢各位的阅读,以上就是“@RabbitListener起作用的原理是什么”的内容了,经过本文的学习后,相信大家对@RabbitListener起作用的原理是什么这一问题有了更深刻的体会,具体使用情况还需要大家实践验证。这里是亿速云,小编将为大家推送更多相关知识点的文章,欢迎关注!
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