idea中原生Servlet3.0开发之---异步请求

骑猪看日落 2022-04-16 01:34 241阅读 0赞

### 一、为什么需要异步请求 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ppbmhhaWppbmc_size_16_color_FFFFFF_t_70][]

当用户的请求很多时，tomcat就会分配一个线程去处理一个请求，这样tomcat线程池中的线程就会不够用，导致请求阻塞的发生；

所以此时，就需要异步请求，即tomcat的线程接收到请求后，不负责后期的处理，而是转发给一个新的线程处理业务模块，如下图

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ppbmhhaWppbmc_size_16_color_FFFFFF_t_70 1][]

主线程结束之后又可以接收新的用户请求，这样就可以处理高并发的情况；

### 二、Servlet3.0中异步请求实现方式 ###

**新建HelloAsyncServlet .java类**

package com.atguigu.servlet;
    
    import java.io.IOException;
    
    import javax.servlet.AsyncContext;
    import javax.servlet.ServletException;
    import javax.servlet.ServletResponse;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    @WebServlet(value="/async",asyncSupported=true)
    public class HelloAsyncServlet extends HttpServlet {
    	
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		//1、支持异步处理asyncSupported=true
    		//2、开启异步模式
    		System.out.println("主线程开始。。。"+Thread.currentThread()+"==>"+System.currentTimeMillis());
    		AsyncContext startAsync = req.startAsync();
    		
    		//3、业务逻辑进行异步处理;开始异步处理
    		startAsync.start(new Runnable() {
    			@Override
    			public void run() {
    				try {
    					System.out.println("副线程开始。。。"+Thread.currentThread()+"==>"+System.currentTimeMillis());
    					sayHello();
    					startAsync.complete();
    					//获取到异步上下文
    					AsyncContext asyncContext = req.getAsyncContext();
    					//4、获取响应
    					ServletResponse response = asyncContext.getResponse();
    					response.getWriter().write("hello async...");
    					System.out.println("副线程结束。。。"+Thread.currentThread()+"==>"+System.currentTimeMillis());
    				} catch (Exception e) {
    				}
    			}
    		});		
    		System.out.println("主线程结束。。。"+Thread.currentThread()+"==>"+System.currentTimeMillis());
    	}
    
    	public void sayHello() throws Exception{
    		System.out.println(Thread.currentThread()+" processing...");
    		Thread.sleep(3000);
    	}
    }

**运行tomcat：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ppbmhhaWppbmc_size_16_color_FFFFFF_t_70 2][]

**结果说明：**主线程结束之后又可以接收新的用户请求，这样就可以处理高并发的情况；

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ppbmhhaWppbmc_size_16_color_FFFFFF_t_70]: /images/20220416/cb6e8a81381d4f17a728b6205789cd24.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ppbmhhaWppbmc_size_16_color_FFFFFF_t_70 1]: /images/20220416/278f463cb1e44fc7875d1a3a54820a7e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ppbmhhaWppbmc_size_16_color_FFFFFF_t_70 2]: /images/20220416/422ef943ebde4709818d31e767437b7c.png