<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns="http://www.springframework.org/schema/integration"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:beans="http://www.springframework.org/schema/beans"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
			https://www.springframework.org/schema/beans/spring-beans.xsd
			http://www.springframework.org/schema/integration
			https://www.springframework.org/schema/integration/spring-integration.xsd">

	<annotation-config/>

	<channel id="oc" >
		<queue/>
	</channel>
	<beans:bean id="Beans" class="com.example.demo.Beans"/>
	
</beans:beans>

@Configuration
public class Beans {
    @ServiceActivator(inputChannel = "ic", outputChannel = "oc")
    public String sayHello(String name) {
        return "Hello " + name;
    }
}

public class HelloWorldDemo {
    @Test
    public void testDemo() throws Exception {
        ClassPathXmlApplicationContext context =
                new ClassPathXmlApplicationContext("/demo.xml", HelloWorldDemo.class);
        DirectChannel inputChannel = context.getBean("ic", DirectChannel.class);
        PollableChannel outputChannel = context.getBean("oc", PollableChannel.class);
        inputChannel.send(new GenericMessage<String>("World"));
        System.out.println("==> HelloWorldDemo: " + outputChannel.receive(0).getPayload());
        context.close();
    }

}

out:
==> HelloWorldDemo: Hello World

@Override
	public void afterPropertiesSet() {
		Assert.notNull(this.beanFactory, "BeanFactory must not be null");
		((BeanDefinitionRegistry) this.beanFactory).registerBeanDefinition(
				IntegrationContextUtils.DISPOSABLES_BEAN_NAME,
				BeanDefinitionBuilder.genericBeanDefinition(Disposables.class, Disposables::new)
						.getRawBeanDefinition());
		this.postProcessors.put(Filter.class, new FilterAnnotationPostProcessor(this.beanFactory));
		this.postProcessors.put(Router.class, new RouterAnnotationPostProcessor(this.beanFactory));
		this.postProcessors.put(Transformer.class, new TransformerAnnotationPostProcessor(this.beanFactory));
		this.postProcessors.put(ServiceActivator.class, new ServiceActivatorAnnotationPostProcessor(this.beanFactory));
		this.postProcessors.put(Splitter.class, new SplitterAnnotationPostProcessor(this.beanFactory));
		this.postProcessors.put(Aggregator.class, new AggregatorAnnotationPostProcessor(this.beanFactory));
		this.postProcessors.put(InboundChannelAdapter.class,
				new InboundChannelAdapterAnnotationPostProcessor(this.beanFactory));
		this.postProcessors.put(BridgeFrom.class, new BridgeFromAnnotationPostProcessor(this.beanFactory));
		this.postProcessors.put(BridgeTo.class, new BridgeToAnnotationPostProcessor(this.beanFactory));
		Map<Class<? extends Annotation>, MethodAnnotationPostProcessor<?>> customPostProcessors =
				setupCustomPostProcessors();
		if (!CollectionUtils.isEmpty(customPostProcessors)) {
			this.postProcessors.putAll(customPostProcessors);
		}
	}

Object result = postProcessor.postProcess(bean, beanName, targetMethod, annotations);

@Override
	public Object postProcess(Object bean, String beanName, Method method, List<Annotation> annotations) {
		Object sourceHandler = null;
		if (beanAnnotationAware() && AnnotatedElementUtils.isAnnotated(method, Bean.class.getName())) {
			if (!this.beanFactory.containsBeanDefinition(resolveTargetBeanName(method))) {
				this.logger.debug("Skipping endpoint creation; perhaps due to some '@Conditional' annotation.");
				return null;
			}
			else {
				sourceHandler = resolveTargetBeanFromMethodWithBeanAnnotation(method);
			}
		}
                //生成對(duì)應(yīng)的MessageHandler，用來(lái)執(zhí)行對(duì)應(yīng)的注解的方法
		MessageHandler handler = createHandler(bean, method, annotations);

		if (!(handler instanceof ReactiveMessageHandlerAdapter)) {
			orderable(method, handler);
			producerOrRouter(annotations, handler);

			if (!handler.equals(sourceHandler)) {
				handler = registerHandlerBean(beanName, method, handler);
			}

			handler = annotated(method, handler);
			handler = adviceChain(beanName, annotations, handler);
		}
                //將MessageHandler實(shí)現(xiàn)連接到消息端點(diǎn)，生成對(duì)應(yīng)的endpoint。
		AbstractEndpoint endpoint = createEndpoint(handler, method, annotations);
		if (endpoint != null) {
			return endpoint;
		}
		else {
			return handler;
		}
	}

@Override
	protected MessageHandler createHandler(Object bean, Method method, List<Annotation> annotations) {
		AbstractReplyProducingMessageHandler serviceActivator;
		if (AnnotatedElementUtils.isAnnotated(method, Bean.class.getName())) {
			...
		else {
			serviceActivator = new ServiceActivatingHandler(bean, method);
		}

		String requiresReply = MessagingAnnotationUtils.resolveAttribute(annotations, "requiresReply", String.class);
		if (StringUtils.hasText(requiresReply)) {
			serviceActivator.setRequiresReply(resolveAttributeToBoolean(requiresReply));
		}

		String isAsync = MessagingAnnotationUtils.resolveAttribute(annotations, "async", String.class);
		if (StringUtils.hasText(isAsync)) {
			serviceActivator.setAsync(resolveAttributeToBoolean(isAsync));
		}
                //是否設(shè)置了輸出通道
		setOutputChannelIfPresent(annotations, serviceActivator);
		return serviceActivator;
	}

	protected AbstractEndpoint createEndpoint(MessageHandler handler, @SuppressWarnings("unused") Method method,
			List<Annotation> annotations) {

		AbstractEndpoint endpoint = null;
                //取得注解中inputChannelName 
		String inputChannelName = MessagingAnnotationUtils.resolveAttribute(annotations, getInputChannelAttribute(),
				String.class);
		if (StringUtils.hasText(inputChannelName)) {
			MessageChannel inputChannel;
			try {
                //從beanFactory中取得對(duì)應(yīng)的通道bean
				inputChannel = this.channelResolver.resolveDestination(inputChannelName);
			}
			catch (DestinationResolutionException e) {
                               //取不到，則自動(dòng)注冊(cè)一個(gè)類(lèi)型為DirectChannel的inputChannel 
				if (e.getCause() instanceof NoSuchBeanDefinitionException) {
					inputChannel = new DirectChannel();
					this.beanFactory.registerSingleton(inputChannelName, inputChannel);
					inputChannel = (MessageChannel) this.beanFactory.initializeBean(inputChannel, inputChannelName);
					if (this.disposables != null) {
						this.disposables.add((DisposableBean) inputChannel);
					}
				}
				else {
					throw e;
				}
			}
			Assert.notNull(inputChannel, () -> "failed to resolve inputChannel '" + inputChannelName + "'");
                        //生成endpoint 
			endpoint = doCreateEndpoint(handler, inputChannel, annotations);
		}
		return endpoint;
	}

protected AbstractEndpoint doCreateEndpoint(MessageHandler handler, MessageChannel inputChannel,
			List<Annotation> annotations) {
		....
		else if (inputChannel instanceof SubscribableChannel) {
                        //生成SubscribableChannel類(lèi)型對(duì)應(yīng)的執(zhí)行端點(diǎn)
			return new EventDrivenConsumer((SubscribableChannel) inputChannel, handler);
		}
		else if (inputChannel instanceof PollableChannel) {
			return pollingConsumer(inputChannel, handler, pollers);
		}
		else {
			throw new IllegalArgumentException("Unsupported 'inputChannel' type: '"
					+ inputChannel.getClass().getName() + "'. " +
					"Must be one of 'SubscribableChannel', 'PollableChannel' or 'ReactiveStreamsSubscribableChannel'");
		}
	}

@Override
	protected void doStart() {
		this.logComponentSubscriptionEvent(true);
                //把handler和inputChannel進(jìn)行綁定
		this.inputChannel.subscribe(this.handler);
		if (this.handler instanceof Lifecycle) {
			((Lifecycle) this.handler).start();
		}
	}

@Override
	public synchronized boolean addHandler(MessageHandler handler) {
		Assert.notNull(handler, "handler must not be null");
		Assert.isTrue(this.handlers.size() < this.maxSubscribers, "Maximum subscribers exceeded");
		boolean added = this.handlers.add(handler);
		if (this.handlers.size() == 1) {
			this.theOneHandler = handler;
		}
		else {
			this.theOneHandler = null;
		}
		return added;
	}

 /**
     *     在此頻道上發(fā)送消息。 如果通道已滿(mǎn)，則此方法將阻塞，直到發(fā)生超時(shí)或發(fā)送線程中斷。 如果指定的超時(shí)時(shí)間為 0，則該方法將立即返回。 如果小于零，它將無(wú)限期阻塞（請(qǐng)參閱send(Message) ）。
     *     參數(shù)：
     *     messageArg – 要發(fā)送的消息
     *     timeout - 以毫秒為單位的超時(shí)時(shí)間
     *     返回：
     *     true如果消息發(fā)送成功， false如果消息無(wú)法在規(guī)定時(shí)間內(nèi)發(fā)送或發(fā)送線程被中斷
     */
	@Override 
	public boolean send(Message<?> messageArg, long timeout) {
		...
		try {
                        //message是否需要轉(zhuǎn)換
			message = convertPayloadIfNecessary(message);
		        //發(fā)送前攔截器
			if (interceptorList.getSize() > 0) {
				interceptorStack = new ArrayDeque<>();
				message = interceptorList.preSend(message, this, interceptorStack);
				if (message == null) {
					return false;
				}
			}
			if (this.metricsCaptor != null) {
				sample = this.metricsCaptor.start();
			}
                        //發(fā)送操作
			sent = doSend(message, timeout);
			if (sample != null) {
				sample.stop(sendTimer(sent));
			}
			metricsProcessed = true;

			if (debugEnabled) {
				logger.debug("postSend (sent=" + sent + ") on channel '" + this + "', message: " + message);
			}
                        //發(fā)送后攔截器
			if (interceptorStack != null) {
				interceptorList.postSend(message, this, sent);
				interceptorList.afterSendCompletion(message, this, sent, null, interceptorStack);
			}
			return sent;
		}
		catch (Exception ex) {
			...
		}
	}

@Override
	protected final void handleMessageInternal(Message<?> message) {
		Object result;
		if (this.advisedRequestHandler == null) {
                        //反射執(zhí)行對(duì)應(yīng)的端點(diǎn)方法
			result = handleRequestMessage(message);
		}
		else {
			result = doInvokeAdvisedRequestHandler(message);
		}
		if (result != null) {
                        //往outputChannel發(fā)送執(zhí)行結(jié)果 
			sendOutputs(result, message);
		}
		...
	}

@Override
	protected boolean doSend(Message<?> message, long timeout) {
		Assert.notNull(message, "'message' must not be null");
		try {
			if (this.queue instanceof BlockingQueue) {
				BlockingQueue<Message<?>> blockingQueue = (BlockingQueue<Message<?>>) this.queue;
				if (timeout > 0) {
					return blockingQueue.offer(message, timeout, TimeUnit.MILLISECONDS);
				}
				if (timeout == 0) {
					return blockingQueue.offer(message);
				}
				blockingQueue.put(message);
				return true;
			}
			else {
				try {
					return this.queue.offer(message);
				}
				finally {
					this.queueSemaphore.release();
				}
			}
		}
		catch (InterruptedException e) {
			Thread.currentThread().interrupt();
			return false;
		}
	}

/**
 *     從該通道接收第一條可用消息。 如果通道不包含任何消息，則此方法將阻塞，直到分配的超時(shí)時(shí)間過(guò)去。 如果指定的超時(shí)時(shí)間為 0，則該方法將立即返回。 如果小于零，它將無(wú)限期阻塞（參見(jiàn)receive() ）。
 *     參數(shù)：
 *     timeout - 以毫秒為單位的超時(shí)時(shí)間
 *     返回：
 *     如果在分配的時(shí)間內(nèi)沒(méi)有可用的消息或接收線程被中斷，則為第一個(gè)可用消息或null 。
 */

	@Override // NOSONAR complexity
	@Nullable
	public Message<?> receive(long timeout) {
		...
		try {
			//接受前攔截器操作
			if (interceptorList.getSize() > 0) {
				interceptorStack = new ArrayDeque<>();
                                //一旦調(diào)用接收并在實(shí)際檢索消息之前調(diào)用
				if (!interceptorList.preReceive(this, interceptorStack)) {
					return null;
				}
			}
                        //接收操作
			Message<?> message = doReceive(timeout);
		        ...
                        //在檢索到 Message 之后但在將其返回給調(diào)用者之前立即調(diào)用。 必要時(shí)可以修改消息
			if (interceptorStack != null && message != null) {
				message = interceptorList.postReceive(message, this);
			}
                        //在接收完成后調(diào)用，而不管已引發(fā)的任何異常，從而允許適當(dāng)?shù)馁Y源清理
			interceptorList.afterReceiveCompletion(message, this, null, interceptorStack);
			return message;
		}
		catch (RuntimeException ex) {
			...
		}
	}

@Override
	@Nullable
	protected Message<?> doReceive(long timeout) {
		try {
			if (timeout > 0) {
				if (this.queue instanceof BlockingQueue) {
					return ((BlockingQueue<Message<?>>) this.queue).poll(timeout, TimeUnit.MILLISECONDS);
				}
				else {
					return pollNonBlockingQueue(timeout);
				}
			}
			if (timeout == 0) {
				return this.queue.poll();
			}

			if (this.queue instanceof BlockingQueue) {
				return ((BlockingQueue<Message<?>>) this.queue).take();
			}
			else {
				Message<?> message = this.queue.poll();
				while (message == null) {
					this.queueSemaphore.tryAcquire(50, TimeUnit.MILLISECONDS); // NOSONAR ok to ignore result
					message = this.queue.poll();
				}
				return message;
			}
		}
		catch (InterruptedException e) {
			Thread.currentThread().interrupt();
			return null;
		}
	}