基于HTTP协议的长轮询在实时性上比上websocket稍有不足，比下HTTP简单轮询有余。

package javax.servlet;

public interface ServletRequest {

    public AsyncContext startAsync();
    
    public AsyncContext startAsync(ServletRequest servletRequest, ServletResponse servletResponse);

}

    HttpServletRequest request; 
    HttpServletResponse response;

    AsyncContext asyncContext = request.startAsync((request, response); //开启异步请求上下文

public class ResourceController {

   private static final String RESOURCE_SAY_HELLO = "SayHello";

   @GetMapping("/waitSayHello")
   public void waitSayHello(HttpServletRequest request, HttpServletResponse response, String who, Integer timeout) {
   
       //请求基础信息
       RequestParam curRequestParam = RequestParam.newInstance(RESOURCE_SAY_HELLO, who);
       //响应超时设置及返回结果
       TimeoutResult timeoutResult = TimeoutResult.newInstance(timeout, "Resp Timeout, but hello world for you!", HttpStatus.REQUEST_TIMEOUT);
       
       //开启异步响应
       AsyncResponseTask.buildAndStart(request, response, curRequestParam, timeoutResult);
   }
}

public class ResourceController {

    private static final String RESOURCE_SAY_HELLO = "SayHello";

    @PutMapping("/sayHello")
    public String sayHelloForWe() {
        final Collection<AsyncResponseTask> sayHelloRespTaskWaitList = AsyncResponseTask.getAsyncTask(RESOURCE_SAY_HELLO);
        final int total = sayHelloRespTaskWaitList.size();

        sayHelloRespTaskWaitList.forEach(asyncResp -> {
            RequestParam requestParam = asyncResp.getRequestParam();
            String who = (String) requestParam.getParam();

            String result = String.format("Hello %s!", who);
            asyncResp.returnJsonResult(result, HttpStatus.OK); //完成异步响应

            log.debug("--->say hello for {} success!", who);
        });

        return String.format("say hello for %s people!", total);
    }
}