Spring Cloud Stream 源码解析

Spring Cloud Stream 是一个消息驱动微服务的框架。
  应用程序通过inputs 或者outputs 来与 Spring Cloud Stream 中binder 交互，通过我们配置来 binding ，而 Spring Cloud Stream 的 binder 负责与消息中间件交互。所以，我们只需要搞清楚如何与 Spring Cloud Stream 交互就可以方便使用消息驱动的方式。
  通过使用Spring Integration来连接消息代理中间件以实现消息事件驱动。Spring Cloud Stream 为一些供应商的消息中间件产品提供了个性化的自动化配置实现，引用了发布-订阅、消费组、分区的三个核心概念。目前仅支持RabbitMQ、Kafka。

下面开始进行分析，首先引入pom文件。

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>1.5.3.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>eureka.stream</groupId>
	<artifactId>stream</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>springstream</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
		<spring-cloud.version>Brixton.SR5</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-stream-rabbit</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
		</dependency>
	</dependencies>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.springframework.cloud</groupId>
				<artifactId>spring-cloud-dependencies</artifactId>
				<version>${spring-cloud.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

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其中spring-cloud-starter-stream-rabbit就是引入的stream的框架，也可以支持spring-cloud-starter-stream-kafka。这里以rabbit做分析。

首先我们先创建一个简单的例子。

先创建消息input、output管道类StreamSendClient。

import org.springframework.cloud.stream.annotation.Input;
import org.springframework.cloud.stream.annotation.Output;
import org.springframework.cloud.stream.messaging.Sink;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.SubscribableChannel;

public interface StreamSendClient {

    @Output("testMessage")
    MessageChannel output();

    @Input("testMessage")
    MessageChannel input();
}

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再创建一个消息处理类SinkReceiver。上面加上@EnableBinding注解。注解定义的类为StreamSendClient。

@EnableBinding({StreamSendClient.class})
public class SinkReceiver {

    @StreamListener("testMessage")
    public void reveive(Object payload){
        System.out.println("Received:" + payload);
    }
}

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创建启动类StreamApplication。

@SpringBootApplication
public class StreamApplication {

	public static void main(String[] args) {
		ConfigurableApplicationContext run = SpringApplication.run(StreamApplication.class, args);
		StreamSendClient streamClient = (StreamSendClient)run.getBean("com.springcloud.eurekaclient.StreamSendClient");
		streamClient.output().send(MessageBuilder.withPayload("from streamClient").build());
	}

}

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执行之后变可以在控制台发现打印信息：Received:from streamClient。同时也可以看到rabbitmq控制台中队列包含了testMessage。

下面开始分析。

首先启动类没有新添任何注解，在SinkReceiver上面有@EnableBinding注解。

@Target({ElementType.TYPE, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Configuration
@Import({ChannelBindingServiceConfiguration.class, BindingBeansRegistrar.class, BinderFactoryConfiguration.class,
		SpelExpressionConverterConfiguration.class})
@EnableIntegration
public @interface EnableBinding {

	/**
	 * A list of interfaces having methods annotated with {@link Input} and/or
	 * {@link Output} to indicate bindable components.
	 */
	Class<?>[] value() default {};

}

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可以知道：

1、该类是一个@Component类

2、该类导入了ChannelBindingServiceConfiguration.class, BindingBeansRegistrar.class, BinderFactoryConfiguration.class, SpelExpressionConverterConfiguration.class类。

3、开启了EnableIntegration注解。Spring Integration的定位是一种企业服务总线 ESB(Enterprise Service Bus),在Spring Integration中，通道被抽象成两种表现形式：PollableChannel和SubscribableChannel，都是继承了MessageChannel。

ChannelBindingServiceConfiguration类分析：

@Configuration
@EnableConfigurationProperties(ChannelBindingServiceProperties.class)
public class ChannelBindingServiceConfiguration {

	private static final String ERROR_CHANNEL_NAME = "error";

	@Autowired
	private MessageBuilderFactory messageBuilderFactory;

	@Autowired(required = false)
	private ObjectMapper objectMapper;

	/**
	 * User defined custom message converters
	 */
	@Autowired(required = false)
	private List<AbstractFromMessageConverter> customMessageConverters;

	@Bean
	// This conditional is intentionally not in an autoconfig (usually a bad idea) because
	// it is used to detect a ChannelBindingService in the parent context (which we know
	// already exists).
	@ConditionalOnMissingBean(ChannelBindingService.class)
	public ChannelBindingService bindingService(ChannelBindingServiceProperties channelBindingServiceProperties,
			BinderFactory<MessageChannel> binderFactory) {
		return new ChannelBindingService(channelBindingServiceProperties, binderFactory);
	}

	@Bean
	public BindableChannelFactory channelFactory(CompositeMessageChannelConfigurer compositeMessageChannelConfigurer) {
		return new DefaultBindableChannelFactory(compositeMessageChannelConfigurer);
	}

	@Bean
	public CompositeMessageChannelConfigurer compositeMessageChannelConfigurer(
			MessageConverterConfigurer messageConverterConfigurer) {
		List<MessageChannelConfigurer> configurerList = new ArrayList<>();
		configurerList.add(messageConverterConfigurer);
		return new CompositeMessageChannelConfigurer(configurerList);
	}

	@Bean
	@DependsOn("bindingService")
	public OutputBindingLifecycle outputBindingLifecycle() {
		return new OutputBindingLifecycle();
	}

	@Bean
	@DependsOn("bindingService")
	public InputBindingLifecycle inputBindingLifecycle() {
		return new InputBindingLifecycle();
	}

	@Bean
	@DependsOn("bindingService")
	public ContextStartAfterRefreshListener contextStartAfterRefreshListener() {
		return new ContextStartAfterRefreshListener();
	}

	@Bean
	public static StreamListenerAnnotationBeanPostProcessor bindToAnnotationBeanPostProcessor(
			@Lazy BinderAwareChannelResolver binderAwareChannelResolver,
			@Lazy MessageHandlerMethodFactory messageHandlerMethodFactory) {
		return new StreamListenerAnnotationBeanPostProcessor(binderAwareChannelResolver,
				messageHandlerMethodFactory);
	}

}

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ChannelBindingServiceConfiguration装载了重要的Bean：

1、ChannelBindingService：负责创建生产者、消费者的MessageChannel，以及RabbitMQ中的交换器（Exchange）、Queue等。

2、inputBindingLifecycle、outputBindingLifecycle：主要负责启动后，调用ChannelBindingService进行创建。

3、StreamListenerAnnotationBeanPostProcessor：负责方法上有@StreamListener注解的方法和RabbitMQ消费channel创建关联关系。即当有rabbitmq消息推送过来，执行方法上有@StreamListener注解的方法。

BindingBeansRegistrar类分析：

BindingBeansRegistrar主要对实现@EnableBinding(StreamSendClient.class)中的class进行分析。

public class BindingBeansRegistrar implements ImportBeanDefinitionRegistrar {

	@Override
	public void registerBeanDefinitions(AnnotationMetadata metadata,
			BeanDefinitionRegistry registry) {
		AnnotationAttributes attrs = AnnotatedElementUtils.getMergedAnnotationAttributes(
				ClassUtils.resolveClassName(metadata.getClassName(), null),
				EnableBinding.class);
		for (Class<?> type : collectClasses(attrs, metadata.getClassName())) {
			BindingBeanDefinitionRegistryUtils.registerChannelBeanDefinitions(type,
					type.getName(), registry);
			BindingBeanDefinitionRegistryUtils.registerChannelsQualifiedBeanDefinitions(
					ClassUtils.resolveClassName(metadata.getClassName(), null), type,
					registry);
		}
	}

	private Class<?>[] collectClasses(AnnotationAttributes attrs, String className) {
		EnableBinding enableBinding = AnnotationUtils.synthesizeAnnotation(attrs,
				EnableBinding.class, ClassUtils.resolveClassName(className, null));
		return enableBinding.value();
	}

}

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通过collectClasses方法，获取EnableBinding中的enableBinding.value()，也就是之前例子中的StreamSendClient类。之后的BindingBeanDefinitionRegistryUtils.registerChannelBeanDefinitions方法

public static void registerChannelBeanDefinitions(Class<?> type,
			final String channelInterfaceBeanName, final BeanDefinitionRegistry registry) {
		ReflectionUtils.doWithMethods(type, new MethodCallback() {
			@Override
			public void doWith(Method method) throws IllegalArgumentException,
					IllegalAccessException {
				Input input = AnnotationUtils.findAnnotation(method, Input.class);
				if (input != null) {
					String name = getChannelName(input, method);
					registerInputChannelBeanDefinition(input.value(), name,
							channelInterfaceBeanName, method.getName(), registry);
				}
				Output output = AnnotationUtils.findAnnotation(method, Output.class);
				if (output != null) {
					String name = getChannelName(output, method);
					registerOutputChannelBeanDefinition(output.value(), name,
							channelInterfaceBeanName, method.getName(), registry);
				}
			}

		});
	}

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public static void registerChannelBeanDefinitions(Class<?> type,
			final String channelInterfaceBeanName, final BeanDefinitionRegistry registry) {
		ReflectionUtils.doWithMethods(type, new MethodCallback() {
			@Override
			public void doWith(Method method) throws IllegalArgumentException,
					IllegalAccessException {
				Input input = AnnotationUtils.findAnnotation(method, Input.class);
				if (input != null) {
					String name = getChannelName(input, method);
					registerInputChannelBeanDefinition(input.value(), name,
							channelInterfaceBeanName, method.getName(), registry);
				}
				Output output = AnnotationUtils.findAnnotation(method, Output.class);
				if (output != null) {
					String name = getChannelName(output, method);
					registerOutputChannelBeanDefinition(output.value(), name,
							channelInterfaceBeanName, method.getName(), registry);
				}
			}

		});
	}

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        public static void registerInputChannelBeanDefinition(String qualifierValue,
			String name, String channelInterfaceBeanName,
			String channelInterfaceMethodName, BeanDefinitionRegistry registry) {
		registerChannelBeanDefinition(Input.class, qualifierValue, name,
				channelInterfaceBeanName, channelInterfaceMethodName, registry);
	}

	private static void registerChannelBeanDefinition(
			Class<? extends Annotation> qualifier, String qualifierValue, String name,
			String channelInterfaceBeanName, String channelInterfaceMethodName,
			BeanDefinitionRegistry registry) {

		RootBeanDefinition rootBeanDefinition = new RootBeanDefinition();
		rootBeanDefinition.setFactoryBeanName(channelInterfaceBeanName);
		rootBeanDefinition.setUniqueFactoryMethodName(channelInterfaceMethodName);
		rootBeanDefinition.addQualifier(new AutowireCandidateQualifier(qualifier,
				qualifierValue));
		registry.registerBeanDefinition(name, rootBeanDefinition);
	}

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找到StreamSendClient类中的@input和@output注解，将两个方法注入成Bean。Bean的名称为StreamSendClient中@Input注解的值，也就是testMessage。并设置定义 BeanDefinition 的生成该Bean的工厂类为StreamSendClient，生成该Bean(testMessage)的方法setUniqueFactoryMethodName为input()。

BindingBeanDefinitionRegistryUtils.registerChannelsQualifiedBeanDefinitions方法：

public static void registerChannelsQualifiedBeanDefinitions(Class<?> parent,
			Class<?> type, final BeanDefinitionRegistry registry) {

		if (type.isInterface()) {
			RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(
					BindableProxyFactory.class);
			rootBeanDefinition.addQualifier(new AutowireCandidateQualifier(
					Bindings.class, parent));
			rootBeanDefinition.getConstructorArgumentValues().addGenericArgumentValue(
					type);
			registry.registerBeanDefinition(type.getName(), rootBeanDefinition);
		}
		else {
			RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(type);
			rootBeanDefinition.addQualifier(new AutowireCandidateQualifier(
					Bindings.class, parent));
			registry.registerBeanDefinition(type.getName(), rootBeanDefinition);
		}
	}

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注入一个beanName为StreamSendClient，Qualifier名为Bindings，BeanClass为BindableProxyFactory（Bindable）类型的Bean对象。BindableProxyFactory实现了Bindable接口。

我们这里在看一下BindableProxyFactory源码。

public class BindableProxyFactory implements MethodInterceptor, FactoryBean<Object>, Bindable, InitializingBean {

	private Map<String, ChannelHolder> inputHolders = new HashMap<>();

	private Map<String, ChannelHolder> outputHolders = new HashMap<>();

	//实现了动态代理，所以当获取input和output方法获取channel时，会通过这里获得
	public synchronized Object invoke(MethodInvocation invocation) throws Throwable {
		MessageChannel messageChannel = null;
		Method method = invocation.getMethod();
		if (MessageChannel.class.isAssignableFrom(method.getReturnType())) {
			Input input = AnnotationUtils.findAnnotation(method, Input.class);
			if (input != null) {
				String name = BindingBeanDefinitionRegistryUtils.getChannelName(input, method);
				messageChannel = this.inputHolders.get(name).getMessageChannel();
			}
			Output output = AnnotationUtils.findAnnotation(method, Output.class);
			if (output != null) {
				String name = BindingBeanDefinitionRegistryUtils.getChannelName(output, method);
				messageChannel =  this.outputHolders.get(name).getMessageChannel();
			}
		}
		//ignore
		return messageChannel;
	}

	//实现了InitializingBean，在Bean生成后，会将input和output两个注解生成对应的channel
        //类，默认是DirectChannel类
	public void afterPropertiesSet() throws Exception {
		ReflectionUtils.doWithMethods(type, new ReflectionUtils.MethodCallback() {
			@Override
			public void doWith(Method method) throws IllegalArgumentException {
				Assert.notNull(channelFactory, "Channel Factory cannot be null");
				Input input = AnnotationUtils.findAnnotation(method, Input.class);
				if (input != null) {
					String name = BindingBeanDefinitionRegistryUtils.getChannelName(input, method);
					validateChannelType(method.getReturnType());
					MessageChannel sharedChannel = locateSharedChannel(name);
					if (sharedChannel == null) {
						inputHolders.put(name, new ChannelHolder(channelFactory.createSubscribableChannel(name), true));
					}
					else {
						inputHolders.put(name, new ChannelHolder(sharedChannel, false));
					}
				}
			}
		});
		ReflectionUtils.doWithMethods(type, new ReflectionUtils.MethodCallback() {
			@Override
			public void doWith(Method method) throws IllegalArgumentException {
				Output output = AnnotationUtils.findAnnotation(method, Output.class);
				if (output != null) {
					String name = BindingBeanDefinitionRegistryUtils.getChannelName(output, method);
					validateChannelType(method.getReturnType());
					MessageChannel sharedChannel = locateSharedChannel(name);
					if (sharedChannel == null) {
						outputHolders.put(name, new ChannelHolder(channelFactory.createSubscribableChannel(name), true));
					}
					else {
						outputHolders.put(name, new ChannelHolder(sharedChannel, false));
					}
				}
			}

		});
	}

	private void validateChannelType(Class<?> channelType) {
		Assert.isTrue(SubscribableChannel.class.equals(channelType) || MessageChannel.class.equals(channelType),
				"A bound channel should be either a '" + MessageChannel.class.getName() + "', " +
						" or a '" + SubscribableChannel.class.getName() + "'");
	}

	private MessageChannel locateSharedChannel(String name) {
		return this.sharedChannelRegistry != null ?
				this.sharedChannelRegistry.get(getNamespacePrefixedChannelName(name)) : null;
	}

	private String getNamespacePrefixedChannelName(String name) {
		return this.channelNamespace + "." + name;
	}

	@Override
	public synchronized Object getObject() throws Exception {
		if (this.proxy == null) {
			ProxyFactory factory = new ProxyFactory(this.type, this);
			this.proxy = factory.getProxy();
		}
		return this.proxy;
	}

	@Override
	public Class<?> getObjectType() {
		return this.type;
	}

	@Override
	public boolean isSingleton() {
		return true;
	}

	public void bindInputs(ChannelBindingService channelBindingService) {
		if (log.isDebugEnabled()) {
			log.debug(String.format("Binding inputs for %s:%s", this.channelNamespace, this.type));
		}
		for (Map.Entry<String, ChannelHolder> channelHolderEntry : this.inputHolders.entrySet()) {
			String inputChannelName = channelHolderEntry.getKey();
			ChannelHolder channelHolder = channelHolderEntry.getValue();
			if (channelHolder.isBindable()) {
				if (log.isDebugEnabled()) {
					log.debug(String.format("Binding %s:%s:%s", this.channelNamespace, this.type, inputChannelName));
				}
				channelBindingService.bindConsumer(channelHolder.getMessageChannel(), inputChannelName);
			}
		}
	}

	@Override
	public void bindOutputs(ChannelBindingService channelBindingService) {
		if (log.isDebugEnabled()) {
			log.debug(String.format("Binding outputs for %s:%s", this.channelNamespace, this.type));
		}
		for (Map.Entry<String, ChannelHolder> channelHolderEntry : this.outputHolders.entrySet()) {
			ChannelHolder channelHolder = channelHolderEntry.getValue();
			String outputChannelName = channelHolderEntry.getKey();
			if (channelHolderEntry.getValue().isBindable()) {
				if (log.isDebugEnabled()) {
					log.debug(String.format("Binding %s:%s:%s", this.channelNamespace, this.type, outputChannelName));
				}
				channelBindingService.bindProducer(channelHolder.getMessageChannel(), outputChannelName);
			}
		}
	}

	@Override
	public void unbindInputs(ChannelBindingService channelBindingService) {
		if (log.isDebugEnabled()) {
			log.debug(String.format("Unbinding inputs for %s:%s", this.channelNamespace, this.type));
		}
		for (Map.Entry<String, ChannelHolder> channelHolderEntry : this.inputHolders.entrySet()) {
			if (channelHolderEntry.getValue().isBindable()) {
				if (log.isDebugEnabled()) {
					log.debug(String.format("Unbinding %s:%s:%s", this.channelNamespace, this.type, channelHolderEntry.getKey()));
				}
				channelBindingService.unbindConsumers(channelHolderEntry.getKey());
			}
		}
	}

	@Override
	public void unbindOutputs(ChannelBindingService channelBindingService) {
		if (log.isDebugEnabled()) {
			log.debug(String.format("Unbinding outputs for %s:%s", this.channelNamespace, this.type));
		}
		for (Map.Entry<String, ChannelHolder> channelHolderEntry : this.outputHolders.entrySet()) {
			if (channelHolderEntry.getValue().isBindable()) {
				if (log.isDebugEnabled()) {
					log.debug(String.format("Binding %s:%s:%s", this.channelNamespace, this.type, channelHolderEntry.getKey()));
				}
				channelBindingService.unbindProducers(channelHolderEntry.getKey());
			}
		}
	}

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BinderFactoryConfiguration类分析

@Configuration
public class BinderFactoryConfiguration {

	@Bean
	@ConditionalOnMissingBean(BinderFactory.class)
	public BinderFactory<?> binderFactory(BinderTypeRegistry binderTypeRegistry,
			ChannelBindingServiceProperties channelBindingServiceProperties) {
		Map<String, BinderConfiguration> binderConfigurations = new HashMap<>();
		Map<String, BinderProperties> declaredBinders = channelBindingServiceProperties.getBinders();
		boolean defaultCandidatesExist = false;
		Iterator<Map.Entry<String, BinderProperties>> binderPropertiesIterator = declaredBinders.entrySet().iterator();
		while (!defaultCandidatesExist && binderPropertiesIterator.hasNext()) {
			defaultCandidatesExist = binderPropertiesIterator.next().getValue().isDefaultCandidate();
		}
		for (Map.Entry<String, BinderProperties> binderEntry : declaredBinders.entrySet()) {
			BinderProperties binderProperties = binderEntry.getValue();
			if (binderTypeRegistry.get(binderEntry.getKey()) != null) {
				binderConfigurations.put(binderEntry.getKey(),
						new BinderConfiguration(binderTypeRegistry.get(binderEntry.getKey()),
								binderProperties.getEnvironment(), binderProperties.isInheritEnvironment(),
								binderProperties.isDefaultCandidate()));
			}
			else {
				Assert.hasText(binderProperties.getType(),
						"No 'type' property present for custom binder " + binderEntry.getKey());
				BinderType binderType = binderTypeRegistry.get(binderProperties.getType());
				Assert.notNull(binderType, "Binder type " + binderProperties.getType() + " is not defined");
				binderConfigurations.put(binderEntry.getKey(),
						new BinderConfiguration(binderType, binderProperties.getEnvironment(),
								binderProperties.isInheritEnvironment(), binderProperties.isDefaultCandidate()));
			}
		}
		if (!defaultCandidatesExist) {
			for (Map.Entry<String, BinderType> entry : binderTypeRegistry.getAll().entrySet()) {
				binderConfigurations.put(entry.getKey(),
						new BinderConfiguration(entry.getValue(), new Properties(), true, true));
			}
		}
		DefaultBinderFactory<?> binderFactory = new DefaultBinderFactory<>(binderConfigurations);
		binderFactory.setDefaultBinder(channelBindingServiceProperties.getDefaultBinder());
		return binderFactory;
	}
}

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主要就是创建一个DefaultBinderFactory的工厂。

ChannelBindingServiceConfiguration, BindingBeansRegistrar, BinderFactoryConfiguration三个装载Bean的内容大概介绍完毕了，现在开始说一下加载过程：

1、ChannelBindingServiceConfiguration类加载的Bean对象outputBindingLifecycle，inputBindingLifecycle。我们拿inputBindingLifecycle做分析，outputBindingLifecycle类似。

	@Bean
	@DependsOn("bindingService")
	public OutputBindingLifecycle outputBindingLifecycle() {
		return new OutputBindingLifecycle();
	}

	@Bean
	@DependsOn("bindingService")
	public InputBindingLifecycle inputBindingLifecycle() {
		return new InputBindingLifecycle();
	}

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inputBindingLifecycle类实现了SmartLifecycle接口，在spring启动后会执行start方法。

public class InputBindingLifecycle implements SmartLifecycle, ApplicationContextAware {
	public void start() {
		if (!running) {
			// retrieve the ChannelBindingService lazily, avoiding early initialization
			try {
				ChannelBindingService channelBindingService = this.applicationContext
						.getBean(ChannelBindingService.class);
				Map<String, Bindable> bindables = this.applicationContext
						.getBeansOfType(Bindable.class);
				for (Bindable bindable : bindables.values()) {
                                        //bindables.values即为@@EnableBinding({StreamSendClient.class})类，BeanClass为BindableProxyFactory
					bindable.bindInputs(channelBindingService);
				}
			}
			catch (BeansException e) {
				throw new IllegalStateException(
						"Cannot perform binding, no proper implementation found", e);
			}
			this.running = true;
		}
	}
}

BindableProxyFactory.bindInputs方法如下：
	public void bindInputs(ChannelBindingService channelBindingService) {
		if (log.isDebugEnabled()) {
			log.debug(String.format("Binding inputs for %s:%s", this.channelNamespace, this.type));
		}
		for (Map.Entry<String, ChannelHolder> channelHolderEntry : this.inputHolders.entrySet()) {
			String inputChannelName = channelHolderEntry.getKey();
			ChannelHolder channelHolder = channelHolderEntry.getValue();
			if (channelHolder.isBindable()) {
				if (log.isDebugEnabled()) {
					log.debug(String.format("Binding %s:%s:%s", this.channelNamespace, this.type, inputChannelName));
				}
                              //这里继续进入
                              channelBindingService.bindConsumer(channelHolder.getMessageChannel(), inputChannelName);
			}
		}

	public Collection<Binding<MessageChannel>> bindConsumer(MessageChannel inputChannel, String inputChannelName) {
		....................
		validate(consumerProperties);
		for (String target : channelBindingTargets) {
                        //继续进入binder.bindConsumer方法
			Binding<MessageChannel> binding = binder.bindConsumer(target, channelBindingServiceProperties.getGroup(inputChannelName), inputChannel, consumerProperties);
			bindings.add(binding);
		}
		this.consumerBindings.put(inputChannelName, bindings);
		return bindings;
	}
	}

会进入RabbitMessageChannelBinder.bindConsumer方法
	public Binding<MessageChannel> doBindConsumer(String name, String group, MessageChannel inputChannel,
			ExtendedConsumerProperties<RabbitConsumerProperties> properties) {

		String prefix = properties.getExtension().getPrefix();
		String exchangeName = applyPrefix(prefix, name);
		TopicExchange exchange = new TopicExchange(exchangeName);
                //创建交换器
		declareExchange(exchangeName, exchange);

		String queueName = applyPrefix(prefix, baseQueueName);
		boolean partitioned = !anonymousConsumer && properties.isPartitioned();
		boolean durable = !anonymousConsumer && properties.getExtension().isDurableSubscription();
		Queue queue;

		......................
                //创建队列
		declareQueue(queueName, queue);

                if (partitioned) {
			String bindingKey = String.format("%s-%d", name, properties.getInstanceIndex());
			declareBinding(queue.getName(), BindingBuilder.bind(queue).to(exchange).with(bindingKey));
		}
		else {
			declareBinding(queue.getName(), BindingBuilder.bind(queue).to(exchange).with("#"));
		}
                Binding<MessageChannel> binding = doRegisterConsumer(baseQueueName, group, inputChannel, queue, properties);
		.................
		return binding;
	}

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可以看到通过inputBindingLifecycle创建了RabbitMq的交换器（Exchange）和队列。

同理通过outputBindingLifecycle启动后会创建生产者。

2、ChannelBindingServiceConfiguration类加载的Bean对象StreamListenerAnnotationBeanPostProcessor。StreamListenerAnnotationBeanPostProcessor实现了BeanPostProcessor接口。会执行postProcessAfterInitialization方法。

public class StreamListenerAnnotationBeanPostProcessor implements BeanPostProcessor, ApplicationContextAware, SmartInitializingSingleton {

    	public Object postProcessAfterInitialization(final Object bean, String beanName) throws BeansException {
		Class<?> targetClass = AopUtils.isAopProxy(bean) ? AopUtils.getTargetClass(bean) : bean.getClass();
		ReflectionUtils.doWithMethods(targetClass, new ReflectionUtils.MethodCallback() {
			@Override
			public void doWith(final Method method) throws IllegalArgumentException, IllegalAccessException {
                                // 步骤1
				StreamListener streamListener = AnnotationUtils.findAnnotation(method, StreamListener.class);
				if (streamListener != null) {
					Method targetMethod = checkProxy(method, bean);
					Assert.hasText(streamListener.value(), "The binding name cannot be null");
                                        //步骤2
					final InvocableHandlerMethod invocableHandlerMethod = messageHandlerMethodFactory.createInvocableHandlerMethod(bean, targetMethod);
					if (!StringUtils.hasText(streamListener.value())) {
						throw new BeanInitializationException("A bound component name must be specified");
					}
					if (mappedBindings.containsKey(streamListener.value())) {
						throw new BeanInitializationException("Duplicate @" + StreamListener.class.getSimpleName() +
								" mapping for '" + streamListener.value() + "' on " + invocableHandlerMethod.getShortLogMessage() +
								" already existing for " + mappedBindings.get(streamListener.value()).getShortLogMessage());
					}
					mappedBindings.put(streamListener.value(), invocableHandlerMethod);
                                        //步骤3
					SubscribableChannel channel = applicationContext.getBean(streamListener.value(),
							SubscribableChannel.class);
					final String defaultOutputChannel = extractDefaultOutput(method);
					if (invocableHandlerMethod.isVoid()) {
						Assert.isTrue(StringUtils.isEmpty(defaultOutputChannel), "An output channel cannot be specified for a method that " +
								"does not return a value");
					}
					else {
						Assert.isTrue(!StringUtils.isEmpty(defaultOutputChannel), "An output channel must be specified for a method that " +
								"can return a value");
					}
                                        //步骤4
					StreamListenerMessageHandler handler = new StreamListenerMessageHandler(invocableHandlerMethod);
					handler.setApplicationContext(applicationContext);
					handler.setChannelResolver(binderAwareChannelResolver);
					if (!StringUtils.isEmpty(defaultOutputChannel)) {
						handler.setOutputChannelName(defaultOutputChannel);
					}
					handler.afterPropertiesSet();
                                        //步骤5
					channel.subscribe(handler);
				}
			}
		});
		return bean;
	}
}

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postProcessAfterInitialization方法过程：

1、会将包含@StreamListener("testMessage")的方法找出来

2、创建一个InvocableHandlerMethod代理类，代理类执行我们创建的具体方法。

3、streamListener.value()的值为testMessage，该Bean实际获取的是工厂类为StreamSendClient，方法为input()获得的Bean对象testMessage。生成该Bean的具体方式上面已经说过在BindingBeanDefinitionRegistryUtils.registerChannelBeanDefinitions方法。将之前由BindableProxyFactory对象通过afterPropertiesSet方法生成的@input、@output注解对应的SubscribableChannel Bean查找出来。

PS:获取testMessage Bean对象时，先找StreamSendClient类，在调用input方法。因为前面设置了rootBeanDefinition.setFactoryBeanName(StreamSendClient);

rootBeanDefinition.setUniqueFactoryMethodName(input);

4、创建一个StreamListenerMessageHandler对象，构造方法中InvocableHandlerMethod作为入参。

5、将SubscribableChannel添加订阅StreamListenerMessageHandler。

这样当消息传过来的时候，就会由StreamListenerMessageHandler中的InvocableHandlerMethod，找到具体方法去处理了。

========分割线-Rabbit消息找对应方法源码深度解析=====================

我们知道刚才RabbitMessageChannelBinder.bindConsumer方法中

RabbitMessageChannelBinder.bindConsumer方法
	public Binding<MessageChannel> doBindConsumer(String name, String group, MessageChannel inputChannel,
			ExtendedConsumerProperties<RabbitConsumerProperties> properties) {

		String prefix = properties.getExtension().getPrefix();
		String exchangeName = applyPrefix(prefix, name);
		TopicExchange exchange = new TopicExchange(exchangeName);
                //创建交换器
		declareExchange(exchangeName, exchange);

		String queueName = applyPrefix(prefix, baseQueueName);
		boolean partitioned = !anonymousConsumer && properties.isPartitioned();
		boolean durable = !anonymousConsumer && properties.getExtension().isDurableSubscription();
		Queue queue;

		......................
                //创建队列
		declareQueue(queueName, queue);

                if (partitioned) {
			String bindingKey = String.format("%s-%d", name, properties.getInstanceIndex());
			declareBinding(queue.getName(), BindingBuilder.bind(queue).to(exchange).with(bindingKey));
		}
		else {
			declareBinding(queue.getName(), BindingBuilder.bind(queue).to(exchange).with("#"));
		}
                Binding<MessageChannel> binding = doRegisterConsumer(baseQueueName, group, inputChannel, queue, properties);
		.................
		return binding;
	}

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最后这句doRegisterConsumer方法就是找到RabbitMq消息对应处理方法的地方。

	private Binding<MessageChannel> doRegisterConsumer(final String name, String group, MessageChannel moduleInputChannel, Queue queue,
			final ExtendedConsumerProperties<RabbitConsumerProperties> properties) {
		DefaultBinding<MessageChannel> consumerBinding;
		SimpleMessageListenerContainer listenerContainer = new SimpleMessageListenerContainer(
				this.connectionFactory);
		listenerContainer.setAcknowledgeMode(properties.getExtension().getAcknowledgeMode());
		listenerContainer.setChannelTransacted(properties.getExtension().isTransacted());
		listenerContainer.setDefaultRequeueRejected(properties.getExtension().isRequeueRejected());
		int concurrency = properties.getConcurrency();
		concurrency = concurrency > 0 ? concurrency : 1;
		listenerContainer.setConcurrentConsumers(concurrency);
		int maxConcurrency = properties.getExtension().getMaxConcurrency();
		if (maxConcurrency > concurrency) {
			listenerContainer.setMaxConcurrentConsumers(maxConcurrency);
		}
		listenerContainer.setPrefetchCount(properties.getExtension().getPrefetch());
		listenerContainer.setRecoveryInterval(properties.getExtension().getRecoveryInterval());
		listenerContainer.setTxSize(properties.getExtension().getTxSize());
		listenerContainer.setTaskExecutor(new SimpleAsyncTaskExecutor(queue.getName() + "-"));
		listenerContainer.setQueues(queue);
		int maxAttempts = properties.getMaxAttempts();
		if (maxAttempts > 1 || properties.getExtension().isRepublishToDlq()) {
			RetryOperationsInterceptor retryInterceptor = RetryInterceptorBuilder.stateless()
					.maxAttempts(maxAttempts)
					.backOffOptions(properties.getBackOffInitialInterval(),
							properties.getBackOffMultiplier(),
							properties.getBackOffMaxInterval())
					.recoverer(determineRecoverer(name, properties.getExtension().getPrefix(), properties.getExtension().isRepublishToDlq()))
					.build();
			listenerContainer.setAdviceChain(new Advice[] { retryInterceptor });
		}
		listenerContainer.setAfterReceivePostProcessors(this.decompressingPostProcessor);
		listenerContainer.setMessagePropertiesConverter(RabbitMessageChannelBinder.inboundMessagePropertiesConverter);
		listenerContainer.afterPropertiesSet();
		AmqpInboundChannelAdapter adapter = new AmqpInboundChannelAdapter(listenerContainer);
		adapter.setBeanFactory(this.getBeanFactory());
		DirectChannel bridgeToModuleChannel = new DirectChannel();
		bridgeToModuleChannel.setBeanFactory(this.getBeanFactory());
		bridgeToModuleChannel.setBeanName(name + ".bridge");
		adapter.setOutputChannel(bridgeToModuleChannel);
		adapter.setBeanName("inbound." + name);
		DefaultAmqpHeaderMapper mapper = new DefaultAmqpHeaderMapper();
		mapper.setRequestHeaderNames(properties.getExtension().getRequestHeaderPatterns());
		mapper.setReplyHeaderNames(properties.getExtension().getReplyHeaderPatterns());
		adapter.setHeaderMapper(mapper);
		adapter.afterPropertiesSet();
		consumerBinding = new DefaultBinding<MessageChannel>(name, group, moduleInputChannel, adapter) {
			@Override
			protected void afterUnbind() {
				cleanAutoDeclareContext(properties.getExtension().getPrefix(), name);
			}
		};
		ReceivingHandler convertingBridge = new ReceivingHandler();
		convertingBridge.setOutputChannel(moduleInputChannel);
		convertingBridge.setBeanName(name + ".convert.bridge");
		convertingBridge.afterPropertiesSet();
		bridgeToModuleChannel.subscribe(convertingBridge);
		adapter.start();
		return consumerBinding;
	}

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1、可以看到Spring Stream的创建了SimpleMessageListenerContainer，该类的作用就是RabbitMQ接收消息并让对应方法处理，在SpringRabbit中是找到@RabbitListener注解，详细分析可以看之前的SpringBoot整合Rabbit的文章。

这里我们只需要知道SimpleMessageListenerContainer是负责和RabbitMQ和本地监听方法交互的一个容器就行。

2、接着创建了一个AmqpInboundChannelAdapter对象，入参是SimpleMessageListenerContainer。并创建了一个名为bridgeToModuleChannel的DirectChannel对象，设置Adapter的OutputChannel为DirectChannel。之后调用adapter的afterPropertiesSet方法。afterPropertiesSet方法会调用自身的onInit方法。

	protected void onInit() {
		this.messageListenerContainer.setMessageListener(new ChannelAwareMessageListener() {

			@Override
			public void onMessage(Message message, Channel channel) throws Exception {
				Object payload = AmqpInboundChannelAdapter.this.messageConverter.fromMessage(message);
				Map<String, Object> headers =
						AmqpInboundChannelAdapter.this.headerMapper.toHeadersFromRequest(message.getMessageProperties());
				if (AmqpInboundChannelAdapter.this.messageListenerContainer.getAcknowledgeMode()
						== AcknowledgeMode.MANUAL) {
					headers.put(AmqpHeaders.DELIVERY_TAG, message.getMessageProperties().getDeliveryTag());
					headers.put(AmqpHeaders.CHANNEL, channel);
				}
				sendMessage(getMessageBuilderFactory().withPayload(payload).copyHeaders(headers).build());
			}

		});
		this.messageListenerContainer.afterPropertiesSet();
		super.onInit();
	}

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onInit方法可以看到，将SimpleMessageListenerContainer的消息监听设置为实现ChannelAwareMessageListener接口的自定义方法。在SpringBoot整合RabbitMQ中，setMessageListener的对象为MessagingMessageListenerAdapter。

3、创建一个ReceivingHandler对象，ReceivingHandler对象实现了MessageHandler接口。并设置ReceivingHandler的OutputChannel为BindableProxyFactory创建的messagechannel。之前已经分析了，在StreamListenerAnnotationBeanPostProcessor对象的postProcessAfterInitialization中，已经将该messagechannel添加了StreamListenerMessageHandler，StreamListenerMessageHandler中又创建了具体的处理Bean和Method。

4、将bridgeToModuleChannel添加观察者ReceivingHandler。

下面分析当一条MQ消息到来时经历的步骤：

1、首先会调用SimpleMessageListenerContainer的onMessage方法，详细分析可以看之前的SpringBoot整合Rabbit的文章。

2、onMessage会调用sendMessage方法。

	public void onMessage(Message message, Channel channel) throws Exception {
				Object payload = AmqpInboundChannelAdapter.this.messageConverter.fromMessage(message);
				Map<String, Object> headers =
						AmqpInboundChannelAdapter.this.headerMapper.toHeadersFromRequest(message.getMessageProperties());
				if (AmqpInboundChannelAdapter.this.messageListenerContainer.getAcknowledgeMode()
						== AcknowledgeMode.MANUAL) {
					headers.put(AmqpHeaders.DELIVERY_TAG, message.getMessageProperties().getDeliveryTag());
					headers.put(AmqpHeaders.CHANNEL, channel);
				}
				sendMessage(getMessageBuilderFactory().withPayload(payload).copyHeaders(headers).build());
	}
        protected void sendMessage(Message<?> message) {
		................
		try {
                        //这里的OutputChannel就是之前的bridgeToModuleChannel
			this.messagingTemplate.send(getOutputChannel(), message);
		}
                ................
	}
	public void send(D destination, Message<?> message) {
		doSend(destination, message);
	}
	protected final void doSend(MessageChannel channel, Message<?> message) {
		......................

		boolean sent = (timeout >= 0 ? channel.send(message, timeout) : channel.send(message));

		..................
	}

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channel.send(message)方法会调用AbstractMessageChannel的send方法

①：

	public final boolean send(Message<?> message, long timeout) {
		Assert.notNull(message, "message must not be null");
		Assert.notNull(message.getPayload(), "message payload must not be null");
		.............
			sent = this.doSend(message, timeout);
			if (countsEnabled) {
				channelMetrics.afterSend(metrics, sent);
				metricsProcessed = true;
			}

			if (debugEnabled) {
				logger.debug("postSend (sent=" + sent + ") on channel '" + this + "', message: " + message);
			}
			if (interceptorStack != null) {
				interceptors.postSend(message, this, sent);
				interceptors.afterSendCompletion(message, this, sent, null, interceptorStack);
			}
			return sent;

		....................
	}

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这里的doSend方法会调用AbstractSubscribableChannel的doSend方法

②：

	protected boolean doSend(Message<?> message, long timeout) {
		try {
			return getRequiredDispatcher().dispatch(message);
		}
		catch (MessageDispatchingException e) {
			String description = e.getMessage() + " for channel '" + this.getFullChannelName() + "'.";
			throw new MessageDeliveryException(message, description, e);
		}
	}
        //UnicastingDispatcher类的dispatch方法
	public final boolean dispatch(final Message<?> message) {
		if (this.executor != null) {
			Runnable task = createMessageHandlingTask(message);
			this.executor.execute(task);
			return true;
		}
		return this.doDispatch(message);
	}

	private boolean doDispatch(Message<?> message) {
		if (this.tryOptimizedDispatch(message)) {
			return true;
		}
		....................
		return success;
	}
	protected boolean tryOptimizedDispatch(Message<?> message) {
		MessageHandler handler = this.theOneHandler;
		if (handler != null) {
			try {
				handler.handleMessage(message);
				return true;
			}
			catch (Exception e) {
				throw wrapExceptionIfNecessary(message, e);
			}
		}
		return false;
	}

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最后会调用handler.handleMessage方法。由刚才创建可知bridgeToModuleChannel的handler为ReceivingHandler。所以会调用ReceivingHandler.handleMessage方法。ReceivingHandler继承自AbstractReplyProducingMessageHandler，AbstractReplyProducingMessageHandler继承自AbstractMessageHandler。所以会调用AbstractMessageHandler.handleMessage方法。

③：

	public final void handleMessage(Message<?> message) {
	        ................
		try {
			............
			this.handleMessageInternal(message);
			............
		}
		catch (Exception e) {
			...........
		}
	}

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之后会执行 AbstractReplyProducingMessageHandler.handleMessageInternal方法

④：

	protected final void handleMessageInternal(Message<?> message) {
		Object result;
		if (this.advisedRequestHandler == null) {
			result = handleRequestMessage(message);
		}
		else {
			result = doInvokeAdvisedRequestHandler(message);
		}
		if (result != null) {
			sendOutputs(result, message);
		}
		else if (this.requiresReply && !isAsync()) {
			throw new ReplyRequiredException(message, "No reply produced by handler '" +
					getComponentName() + "', and its 'requiresReply' property is set to true.");
		}
		else if (!isAsync() && logger.isDebugEnabled()) {
			logger.debug("handler '" + this + "' produced no reply for request Message: " + message);
		}
	}

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会执行ReceivingHandler.handleRequestMessage方法,对消息进行反序列化等。之后会执行sendOutputs。

	protected void sendOutputs(Object result, Message<?> requestMessage) {
		if (result instanceof Iterable<?> && shouldSplitOutput((Iterable<?>) result)) {
			for (Object o : (Iterable<?>) result) {
				this.produceOutput(o, requestMessage);
			}
		}
		else if (result != null) {
			this.produceOutput(result, requestMessage);
		}
	}

	protected void produceOutput(Object reply, final Message<?> requestMessage) {
		final MessageHeaders requestHeaders = requestMessage.getHeaders();

		Object replyChannel = null;
		if (getOutputChannel() == null) {
			............

		}

		if (this.async && reply instanceof ListenableFuture<?>) {
		    .......................
		}
		else {
			sendOutput(createOutputMessage(reply, requestHeaders), replyChannel, false);
		}
	}

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	protected void sendOutput(Object output, Object replyChannel, boolean useArgChannel) {
		MessageChannel outputChannel = getOutputChannel();
		....................

		if (replyChannel instanceof MessageChannel) {
			if (output instanceof Message<?>) {
				this.messagingTemplate.send((MessageChannel) replyChannel, (Message<?>) output);
			}
			else {
				this.messagingTemplate.convertAndSend((MessageChannel) replyChannel, output);
			}
		}
		..................
	}

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此处ReceivingHandler.sendOutput的getOutputChannel就是BindableProxyFactory创建的messagechannel。

3、之后会调用this.messagingTemplate.send((MessageChannel) replyChannel, (Message<?>) output);也就是重复之前的①、②、③、④步骤。进入到AbstractReplyProducingMessageHandler.handleMessageInternal方法。

	protected final void handleMessageInternal(Message<?> message) {
		Object result;
		if (this.advisedRequestHandler == null) {
			result = handleRequestMessage(message);
		}
		else {
			result = doInvokeAdvisedRequestHandler(message);
		}
		if (result != null) {
			sendOutputs(result, message);
		}
		else if (this.requiresReply && !isAsync()) {
			throw new ReplyRequiredException(message, "No reply produced by handler '" +
					getComponentName() + "', and its 'requiresReply' property is set to true.");
		}
		else if (!isAsync() && logger.isDebugEnabled()) {
			logger.debug("handler '" + this + "' produced no reply for request Message: " + message);
		}
	}

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但是此时的messagechannel是BindableProxyFactory创建的，此时的观察者是StreamListenerMessageHandler。

		protected Object handleRequestMessage(Message<?> requestMessage) {
			try {
				return invocableHandlerMethod.invoke(requestMessage);
			}
			catch (Exception e) {
				if (e instanceof MessagingException) {
					throw (MessagingException) e;
				}
				else {
					throw new MessagingException(requestMessage, "Exception thrown while invoking " + invocableHandlerMethod.getShortLogMessage(), e);
				}
			}
		}

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由之前源码解析可知，invocableHandlerMethod已经封装了对应的Bean和Method。这样就完成了从RabbitMQ到Spring Stream找到对应方法的解析。

Spring Stream Rabbit消息找对应方法源码总结：

1、Spring Stream的创建了SimpleMessageListenerContainer，用于监听RabbitMQ服务器。

2、创建一个AmqpInboundChannelAdapter对象，入参是SimpleMessageListenerContainer。两者做关联，让SimpleMessageListenerContainer收到信息后，调用AmqpInboundChannelAdapter中onInit方法里创建的onMessage信息。

3、创建一个名为bridgeToModuleChannel的DirectChannel对象，设置Adapter的OutputChannel为DirectChannel。

4、创建一个观察者ReceivingHandler，用于观察bridgeToModuleChannel。并设置ReceivingHandler的OutputChannel为BindableProxyFactory创建的messagechannel。

5、RabbitMQ发送信息后，第一次会到ReceivingHandler.handleRequestMessage方法,对消息进行反序列化等。之后会执行sendOutputs。

6、再次sendOutputs后，会调用BindableProxyFactory创建的messagechannel的观察者StreamListenerMessageHandler。StreamListenerMessageHandler.handleRequestMessage方法会通过invocableHandlerMethod调用已经封装了对应的Bean和Method。从而找到对应的类方法。

以上就是Spring Cloud Stream的简单分析，Spring Stream的使用需要结合Spring Integration。