Detailed explanation of Spring Boot's two asynchronous request methods

Asynchronous processing of requests has been added in spring 3.2 and later versions. This article mainly introduces Spring Boot to implement asynchronous requests (Servlet 3.0). Interested friends can refer to it.

Asynchronous processing of requests has been added in spring 3.2 and later versions, aiming to increase the processing speed of requests and reduce service performance consumption.

We have done time-consuming processing in our request. In the case of concurrent requests, in order to avoid performance problems caused by long-term occupation of the web server's connection pool, a non-web service thread is generated after the call is made for processing. , increase the throughput of the web server.

For this reason, Servlet 3.0 adds asynchronous processing of requests, and Spring also performs encapsulation processing on this basis.

This article still uses code examples to explain how to apply asynchronous requests in Spring Boot.

First let me talk about a few key points:

1. asyncSupported = true in @WebFilter and @WebServlet annotations Attributes

If there is a filter for the asynchronously processed servlet, the annotation @WebFilter of the filter should be set asyncSupported=true,

Otherwise, an error A filter or will be reported servlet of the current chain does not support asynchronous operations.

2. @EnableAsync annotation

Spring Boot adds some filters to intercept /* by default. Because /* will intercept all requests, it stands to reason that we should also set the asyncSupported=true attribute. Because these filters are initialized by Spring Boot, it provides the @EnableAsync annotation for unified configuration. This annotation is only valid for "non-@WebFilter and @WebServlet annotations", so the Filter we define still needs to configure asyncSupported= ourselves. true.

3. AsyncContext Object

Get the context object of an asynchronous request.

4. asyncContext.setTimeout(20 * 1000L);

We cannot let asynchronous requests wait indefinitely, and set the maximum timeout through setTimeout .

There are two ways to test asynchronous tasks:

First add the @EnableAsync annotation on SpringBootSampleApplication.

Check all custom Filters again. If there are two situations below, you need to configure asyncSupported=true

1) Custom Filter intercepts /*

2) A certain Filter intercepts /shanhy/*, and the Servlet we need to execute the asynchronous request is /shanhy/testcomet

Method 1: Native Servlet method

package org.springboot.sample.servlet;

import java.io.IOException;
import java.util.Queue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;

import javax.servlet.AsyncContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * HTTP长连接实现
 *
 * @author 单红宇(365384722)
 * @myblog http://blog.csdn.net/catoop/
 * @create 2016年3月29日
 */
@WebServlet(urlPatterns = "/xs/cometservlet", asyncSupported = true)
//异步处理的servlet若存在过滤器，则过滤器的注解@WebFilter应设置asyncSupported=true，
//否则会报错A filter or servlet of the current chain does not support asynchronous operations.
public class CometServlet extends HttpServlet {

 private static final long serialVersionUID = -8685285401859800066L;

 private final Queue<AsyncContext> asyncContexts = new LinkedBlockingQueue<>();

 private final Thread generator = new Thread("Async Event generator") {

  @Override
  public void run() {
   while (!generator.isInterrupted()) {// 线程有效
    try {
     while (!asyncContexts.isEmpty()) {// 不为空
      TimeUnit.SECONDS.sleep(10);// 秒，模拟耗时操作
      AsyncContext asyncContext = asyncContexts.poll();
      HttpServletResponse res = (HttpServletResponse) asyncContext.getResponse();
      res.getWriter().write("{\"result\":\"OK - "+System.currentTimeMillis()+"\"}");
      res.setStatus(HttpServletResponse.SC_OK);
      res.setContentType("application/json");
      asyncContext.complete();// 完成
     }
    } catch (InterruptedException e) {
     Thread.currentThread().interrupt();
     e.printStackTrace();
    } catch (IOException e) {
     e.printStackTrace();
    }
   }
  }

 };

 @Override
 public void init() throws ServletException {
  super.init();
  generator.start();
 }

 @Override
 protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  System.out.println(">>>>>>>>>>CometServlet Request<<<<<<<<<<<");
  doPost(req, resp);
 }

 @Override
 protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  AsyncContext asyncContext = req.startAsync();
  asyncContext.setTimeout(20 * 1000L);
  asyncContexts.offer(asyncContext);
 }

 @Override
 public void destroy() {
  super.destroy();
  generator.interrupt();
 }
}

Method 2: Controller method

@Controller
public class PageController {

 @RequestMapping("/async/test")
 @ResponseBody
 public Callable<String> callable() {
  // 这么做的好处避免web server的连接池被长期占用而引起性能问题，
  // 调用后生成一个非web的服务线程来处理，增加web服务器的吞吐量。
  return new Callable<String>() {
   @Override
   public String call() throws Exception {
    Thread.sleep(3 * 1000L);
    return "小单 - " + System.currentTimeMillis();
   }
  };
 }

}

Finally write a comet.jsp page test:

<%@ page pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
 <title>长连接测试</title>
 <script type="text/javascript" src="${pageContext.request.contextPath }/webjarslocator/jquery/jquery.js"></script>
 <script type="text/javascript">
  $(function(){
   function longPolling(){
    $.getJSON(&#39;${pageContext.request.contextPath }/xs/cometservlet&#39;, function(data){
     console.log(data.result);
     $(&#39;#n1&#39;).html(data.result);
     longPolling();
    });
   }
   longPolling();

   function longPolling2(){
    $.get(&#39;${pageContext.request.contextPath }/async/test&#39;, function(data){
     console.log(data);
     $(&#39;#n2&#39;).html(data);
     longPolling2();
    });
   }
   longPolling2();
  });
 </script>
 </head>

 <body>
 <h1 id="长连接测试">长连接测试</h1>
 <h2 id="n1"></h2>
 <h2 id="n2"></h2>
 </body>
</html>

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