ChannelInterceptor：

• Message被髮送到執行緒池，在傳送動作執行前（後）攔截，發生在當前執行緒。

ExecutorChannelInterceptor：

• Message被髮送到執行緒池後，線上程池持有的新執行緒中，在MessageHandler處理前（後）攔截。

這裡以，為InboundChannel配置ChannelInterceptor為例

1. 在WebSocketMessageBrokerConfigurer中配置攔截器：

WebSocketMessageBrokerConfigurer:
 @Override
	public void configureClientInboundChannel
 
(ChannelRegistration registration) {
		registration.interceptors(new ChannelInterceptor() {
			 @Override
			 public Message<?> preSend(Message<?> message, MessageChannel channel) {
			        StompHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, StompHeaderAccessor.class
 
);
			        StompCommand command = accessor.getCommand();
			        log.info(command.toString());
			        log.info(JSON.toJSONString(message));
			        if (StompCommand.CONNECT.equals(accessor.getCommand())) {
			        	//群聊：表示roomId；私聊：表示userId
			        	String id = accessor.getFirstNativeHeader
 
("id");
			        	accessor.setUser(new IdPrincipal(id));
			        }
			        return message;
			 }

		});
	}

2. 從WebSocketMessageBrokerConfigurer配置中讀取登記過的攔截器

AbstractMessageBrokerConfiguration:
	@Bean
	public AbstractSubscribableChannel clientInboundChannel() {
		ExecutorSubscribableChannel channel = new ExecutorSubscribableChannel(clientInboundChannelExecutor());
		ChannelRegistration reg = getClientInboundChannelRegistration();
		if (reg.hasInterceptors()) {
			channel.setInterceptors(reg.getInterceptors());
		}
		return channel;
	}

3. 將通道攔截器繫結到ExecutorSubscribableChannel上，同時為攔截器分類ChannelInterceptor和ExecutorChannelInterceptor，新增到相應集合中

ExecutorSubscribableChannel:
	@Override
	public void setInterceptors(List<ChannelInterceptor> interceptors) {
		super.setInterceptors(interceptors);
		this.executorInterceptors.clear();
		for (ChannelInterceptor interceptor : interceptors) {
			if (interceptor instanceof ExecutorChannelInterceptor) {
				this.executorInterceptors.add((ExecutorChannelInterceptor) interceptor);
			}
		}
	}

4. 普通的ChannelInterceptor，被內部類AbstractMessageChannel$ChannelInterceptorChain構造成攔截器鏈，這個攔截器鏈的所有實現方法都以外部類AbstractMessageChannel例項所持有的interceptors集合為核心，進行攔截器的呼叫。
5. 攔截器鏈的呼叫發生在AbstractMessageChannel例項的send方法中，在sendInternal方法執行前後同步呼叫，發生在當前執行緒。

AbstractMessageChannel:

public abstract class AbstractMessageChannel implements MessageChannel, InterceptableChannel, BeanNameAware {

	private final List<ChannelInterceptor> interceptors = new ArrayList<ChannelInterceptor>(5);

	@Override
	public final boolean send(Message<?> message, long timeout) {
		Assert.notNull(message, "Message must not be null");
		ChannelInterceptorChain chain = new ChannelInterceptorChain();
		boolean sent = false;
		try {
			message = chain.applyPreSend(message, this);
			if (message == null) {
				return false;
			}
			sent = sendInternal(message, timeout);
			chain.applyPostSend(message, this, sent);
			chain.triggerAfterSendCompletion(message, this, sent, null);
			return sent;
		}
		catch (Exception ex) {
			chain.triggerAfterSendCompletion(message, this, sent, ex);
			if (ex instanceof MessagingException) {
				throw (MessagingException) ex;
			}
			throw new MessageDeliveryException(message,"Failed to send message to " + this, ex);
		}
		catch (Throwable err) {
			MessageDeliveryException ex2 =
					new MessageDeliveryException(message, "Failed to send message to " + this, err);
			chain.triggerAfterSendCompletion(message, this, sent, ex2);
			throw ex2;
		}
	}

	/**
	 * Assists with the invocation of the configured channel interceptors.
	 */
	protected class ChannelInterceptorChain {
		private int sendInterceptorIndex = -1;
		private int receiveInterceptorIndex = -1;
		
		public Message<?> applyPreSend(Message<?> message, MessageChannel channel) {
			Message<?> messageToUse = message;
			for (ChannelInterceptor interceptor : interceptors) {
				Message<?> resolvedMessage = interceptor.preSend(messageToUse, channel);
				if (resolvedMessage == null) {
					String name = interceptor.getClass().getSimpleName();
					if (logger.isDebugEnabled()) {
						logger.debug(name + " returned null from preSend, i.e. precluding the send.");
					}
					triggerAfterSendCompletion(messageToUse, channel, false, null);
					return null;
				}
				messageToUse = resolvedMessage;
				this.sendInterceptorIndex++;
			}
			return messageToUse;
		}
		public void applyPostSend(Message<?> message, MessageChannel channel, boolean sent) {
			for (ChannelInterceptor interceptor : interceptors) {
				interceptor.postSend(message, channel, sent);
			}
		}
      
        /**
         *其他方法
         */
	}

}

6. InboundChannel例項通過sendInternal方法，將Message與MessageHandler封裝成SendTask，傳送到支撐自己的ThreadPoolTaskExecutor執行緒池，在新的執行緒中非同步處理Message；
7. 在新的執行緒中，在SendTask的run方法裡，通過MessageHandler.handleMessage(Message)方法對Message進行處理，在handleMessage前後呼叫executorInterceptors集合，進行攔截；

ExecutorSubscribableChannel :

public class ExecutorSubscribableChannel extends AbstractSubscribableChannel {
	private final Executor executor;
	private final List<ExecutorChannelInterceptor> executorInterceptors = new ArrayList<ExecutorChannelInterceptor>(4);
	
	@Override
	public boolean sendInternal(Message<?> message, long timeout) {
		for (MessageHandler handler : getSubscribers()) {
			SendTask sendTask = new SendTask(message, handler);
			if (this.executor == null) {
				sendTask.run();
			}
			else {
				this.executor.execute(sendTask);
			}
		}
		return true;
	}
	/**
	 * Invoke a MessageHandler with ExecutorChannelInterceptors.
	 */
	private class SendTask implements MessageHandlingRunnable {
		@Override
		public void run() {
			Message<?> message = this.inputMessage;
			try {
				message = applyBeforeHandle(message);
				if (message == null) {
					return;
				}
				this.messageHandler.handleMessage(message);
				triggerAfterMessageHandled(message, null);
			}
			catch (Exception ex) {
				triggerAfterMessageHandled(message, ex);
				if (ex instanceof MessagingException) {
					throw (MessagingException) ex;
				}
				String description = "Failed to handle " + message + " to " + this + " in " + this.messageHandler;
				throw new MessageDeliveryException(message, description, ex);
			}
			catch (Throwable err) {
				String description = "Failed to handle " + message + " to " + this + " in " + this.messageHandler;
				MessageDeliveryException ex2 = new MessageDeliveryException(message, description, err);
				triggerAfterMessageHandled(message, ex2);
				throw ex2;
			}
		}

		private Message<?> applyBeforeHandle(Message<?> message) {
			Message<?> messageToUse = message;
			for (ExecutorChannelInterceptor interceptor : executorInterceptors) {
				messageToUse = interceptor.beforeHandle(messageToUse, ExecutorSubscribableChannel.this, this.messageHandler);
				if (messageToUse == null) {
					String name = interceptor.getClass().getSimpleName();
					if (logger.isDebugEnabled()) {
						logger.debug(name + " returned null from beforeHandle, i.e. precluding the send.");
					}
					triggerAfterMessageHandled(message, null);
					return null;
				}
				this.interceptorIndex++;
			}
			return messageToUse;
		}

		private void triggerAfterMessageHandled(Message<?> message, Exception ex) {
			for (int i = this.interceptorIndex; i >= 0; i--) {
				ExecutorChannelInterceptor interceptor = executorInterceptors.get(i);
				try {
					interceptor.afterMessageHandled(message, ExecutorSubscribableChannel.this, this.messageHandler, ex);
				}
				catch (Throwable ex2) {
					logger.error("Exception from afterMessageHandled in " + interceptor, ex2);
				}
			}
		}
	}

}