@WebServlet(urlPatterns = "/async",asyncSupported = true)
@Slf4j
public class AsyncServlet extends HttpServlet {

 ExecutorService executorService =Executors.newSingleThreadExecutor();

 @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  //開啟異步,獲取異步上下文
  final AsyncContext ctx = req.startAsync();
  // 提交線程池異步執(zhí)行
  executorService.execute(new Runnable() {


   @Override
   public void run() {
    try {
     log.info("async Service 準(zhǔn)備執(zhí)行了");
     //模擬耗時(shí)任務(wù)
     Thread.sleep(10000L);
     ctx.getResponse().getWriter().print("async servlet");
     log.info("async Service 執(zhí)行了");
    } catch (IOException e) {
     e.printStackTrace();
    } catch (InterruptedException e) {
     e.printStackTrace();
    }
    //最后執(zhí)行完成后完成回調(diào)。
    ctx.complete();
   }
  });
 }

 public AsyncContext startAsync(ServletRequest request,
   ServletResponse response) {
  if (!isAsyncSupported()) {
   IllegalStateException ise =
     new IllegalStateException(sm.getString("request.asyncNotSupported"));
   log.warn(sm.getString("coyoteRequest.noAsync",
     StringUtils.join(getNonAsyncClassNames())), ise);
   throw ise;
  }

  if (asyncContext == null) {
   asyncContext = new AsyncContextImpl(this);
  }

  asyncContext.setStarted(getContext(), request, response,
    request==getRequest() && response==getResponse().getResponse());
  asyncContext.setTimeout(getConnector().getAsyncTimeout());

  return asyncContext;
 }

 public void complete() {
  if (log.isDebugEnabled()) {
   logDebug("complete ");
  }
  check();
  request.getCoyoteRequest().action(ActionCode.ASYNC_COMPLETE, null);
 }
//類：AbstractProcessor 
 public final void action(ActionCode actionCode, Object param) {
 case ASYNC_COMPLETE: {
   clearDispatches();
   if (asyncStateMachine.asyncComplete()) {
    processSocketEvent(SocketEvent.OPEN_READ, true);
   }
   break;
  } 
 }
 //類：AbstractProcessor 
protected void processSocketEvent(SocketEvent event, boolean dispatch) {
  SocketWrapperBase<?> socketWrapper = getSocketWrapper();
  if (socketWrapper != null) {
   socketWrapper.processSocket(event, dispatch);
  }
 }
 //類：AbstractEndpoint
public boolean processSocket(SocketWrapperBase<S> socketWrapper,
   SocketEvent event, boolean dispatch) {
  //省略部分代碼
   SocketProcessorBase<S> sc = null;
   if (processorCache != null) {
    sc = processorCache.pop();
   }
   if (sc == null) {
    sc = createSocketProcessor(socketWrapper, event);
   } else {
    sc.reset(socketWrapper, event);
   }
   Executor executor = getExecutor();
   if (dispatch && executor != null) {
    executor.execute(sc);
   } else {
    sc.run();
   }
 
  return true;
 }

類：AbstractProcessorLight
public SocketState process(SocketWrapperBase<?> socketWrapper, SocketEvent status)
   throws IOException {
  //省略部分diam
  SocketState state = SocketState.CLOSED;
  Iterator<DispatchType> dispatches = null;
  do {
   if (dispatches != null) {
    DispatchType nextDispatch = dispatches.next();
    state = dispatch(nextDispatch.getSocketStatus());
   } else if (status == SocketEvent.DISCONNECT) {
   
   } else if (isAsync() || isUpgrade() || state == SocketState.ASYNC_END) {
    state = dispatch(status);
    if (state == SocketState.OPEN) {
     state = service(socketWrapper);
    }
   } else if (status == SocketEvent.OPEN_WRITE) {
    state = SocketState.LONG;
   } else if (status == SocketEvent.OPEN_READ){
    state = service(socketWrapper);
   } else {
    state = SocketState.CLOSED;
   }

  } while (state == SocketState.ASYNC_END ||
    dispatches != null && state != SocketState.CLOSED);

  return state;
 }

public boolean asyncDispatch(org.apache.coyote.Request req, org.apache.coyote.Response res,
   SocketEvent status) throws Exception {
  //省略部分代碼
  Request request = (Request) req.getNote(ADAPTER_NOTES);
  Response response = (Response) res.getNote(ADAPTER_NOTES);
  boolean success = true;
  AsyncContextImpl asyncConImpl = request.getAsyncContextInternal();
  try {
   if (!request.isAsync()) {
    response.setSuspended(false);
   }

   if (status==SocketEvent.TIMEOUT) {
    if (!asyncConImpl.timeout()) {
     asyncConImpl.setErrorState(null, false);
    }
   } else if (status==SocketEvent.ERROR) {
    
   }

   if (!request.isAsyncDispatching() && request.isAsync()) {
    WriteListener writeListener = res.getWriteListener();
    ReadListener readListener = req.getReadListener();
    if (writeListener != null && status == SocketEvent.OPEN_WRITE) {
     ClassLoader oldCL = null;
     try {
      oldCL = request.getContext().bind(false, null);
      res.onWritePossible();//這里執(zhí)行瀏覽器響應(yīng)，寫入數(shù)據(jù)
      if (request.isFinished() && req.sendAllDataReadEvent() &&
        readListener != null) {
       readListener.onAllDataRead();
      }
     } catch (Throwable t) {
      
     } finally {
      request.getContext().unbind(false, oldCL);
     }
    } 
    }
   }
   //這里判斷異步正在進(jìn)行，說明這不是一個(gè)完成方法的回調(diào)，是一個(gè)正常異步請求，繼續(xù)調(diào)用容器。
   if (request.isAsyncDispatching()) {
    connector.getService().getContainer().getPipeline().getFirst().invoke(
      request, response);
    Throwable t = (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION);
    if (t != null) {
     asyncConImpl.setErrorState(t, true);
    }
   }
   //注意，這里，如果超時(shí)或者出錯(cuò)，request.isAsync()會返回false，這里是為了盡快的輸出錯(cuò)誤給客戶端。
   if (!request.isAsync()) {
    //這里也是輸出邏輯
    request.finishRequest();
    response.finishResponse();
   }
   //銷毀request和response
   if (!success || !request.isAsync()) {
    updateWrapperErrorCount(request, response);
    request.recycle();
    response.recycle();
   }
  }
  return success;
 }

 postParseSuccess = postParseRequest(req, request, res, response);
   //省略部分代碼
   if (postParseSuccess) {
    request.setAsyncSupported(
      connector.getService().getContainer().getPipeline().isAsyncSupported());
    connector.getService().getContainer().getPipeline().getFirst().invoke(
      request, response);
   }
   if (request.isAsync()) {
    async = true;
    } else {
    //輸出數(shù)據(jù)到客戶端
    request.finishRequest();
    response.finishResponse();
   if (!async) {
    updateWrapperErrorCount(request, response);
    //銷毀request和response
    request.recycle();
    response.recycle();
   }

@RestController
@Slf4j
public class TestController {
 @Autowired
 private TestService service;

 @GetMapping("/hello")
 public String test() {
  try {
   log.info("testAsynch Start");
   CompletableFuture<String> test1 = service.test1();
   CompletableFuture<String> test2 = service.test2();
   CompletableFuture<String> test3 = service.test3();
   CompletableFuture.allOf(test1, test2, test3);
   log.info("test1=====" + test1.get());
   log.info("test2=====" + test2.get());
   log.info("test3=====" + test3.get());
  } catch (InterruptedException e) {
   e.printStackTrace();
  } catch (ExecutionException e) {
   e.printStackTrace();
  }
  return "hello";
 }
@Service
public class TestService {
 @Async("asyncExecutor")
 public CompletableFuture<String> test1() throws InterruptedException {
  Thread.sleep(3000L);
  return CompletableFuture.completedFuture("test1");
 }

 @Async("asyncExecutor")
 public CompletableFuture<String> test2() throws InterruptedException {
  Thread.sleep(3000L);
  return CompletableFuture.completedFuture("test2");
 }

 @Async("asyncExecutor")
 public CompletableFuture<String> test3() throws InterruptedException {
  Thread.sleep(3000L);
  return CompletableFuture.completedFuture("test3");
 }
}
@SpringBootApplication
@EnableAsync
public class TomcatdebugApplication {

 public static void main(String[] args) {
  SpringApplication.run(TomcatdebugApplication.class, args);
 }

 @Bean(name = "asyncExecutor")
 public Executor asyncExecutor() {
  ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
  executor.setCorePoolSize(3);
  executor.setMaxPoolSize(3);
  executor.setQueueCapacity(100);
  executor.setThreadNamePrefix("AsynchThread-");
  executor.initialize();
  return executor;
 }