学习Servlet中的异步处理 —— Servlet3.0中的Async支持

servlet的@WebServlet注解写法：

/**
 * asyncSupported属性默认是false,如果需要开启支持异步处理功能,需要设置为true
 */
@WebServlet(name = "ServletAsyn", urlPatterns = "/ServletAsyn", asyncSupported = true)

AsynFilter的@WebServlet注解写法：

@WebFilter(filterName="AsynFilter",asyncSupported=true,value={"/ServletAsyn"},dispatcherTypes={DispatcherType.REQUEST,DispatcherType.ASYNC})

测试过程:

打开浏览器输入项目servlet地址:
http://localhost:8080/ServletAsynFilter/ServletAsyn

后台输出如图：

浏览器输出如图：

总结：

输入servlet请求地址，出发过滤器，过滤器方法开始执行，然后servlet的dopost方法开始执行，于是，创建了内部类的一个异步线程。在线程还没有完成的时候，servlet继续往下执行。最后，线程的任务完成返回浏览器页面。

下面是代码：
ServletAsyn.java

 package servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.text.SimpleDateFormat;
import java.util.Date;

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;

/**
 * autor:xanwidtf@foxmail.com
 */
/**
 * Servlet implementation class ServletAsyn
 */
@WebServlet(name = "ServletAsyn", urlPatterns = "/ServletAsyn", asyncSupported = true)
public class ServletAsyn extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public ServletAsyn() {
        super();
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        //response.getWriter().append("Served at: ").append(request.getContextPath());

        System.out.println("Servlet执行开始时间："+new Date());
          response.setCharacterEncoding("utf-8");
          response.setContentType("text/html;charset=utf-8");
          PrintWriter out = response.getWriter();
          Date date = new Date(System.currentTimeMillis());
          SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
          out.print("<h1>");
          out.println("Servlet  begin --" + sdf.format(date) + "<br>");// 响应输出到客户端
          out.print("</h1>");
          out.print("<hr>");

        /*
         * 体现异步思想，Servlet执行结束，而异步的线程仍然在继续跑
         */
        AsyncContext context=request.startAsync();
        new Thread(new Executor(context)).start(); //new Thread 传递AsyncContext对象   并且start
        System.out.println("Servlet执行结束时间："+new Date());
    }

    //内部类实现线程
    public class Executor implements Runnable{
        private AsyncContext context;
        public Executor(AsyncContext context){
            this.context=context;
        }

        @Override
        public void run() {
            //执行相关复杂业务
            try {
                Thread.sleep(1000*3);
                context.getRequest();
                context.getResponse();
                 ServletResponse response = context.getResponse();
                    PrintWriter out = response.getWriter();
                    Date date = new Date(System.currentTimeMillis());
                    SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");

                    out.print("<h1>");
                    out.println("Thread worker finished --"+ sdf.format(date));// 响应输出到客户端
                    out.print("</h1><hr>");
                    out.flush();
                    System.out.println("业务完成时间:"+new Date());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

Filter.java

package Filter;

import java.io.IOException;

import javax.servlet.DispatcherType;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;

@WebFilter(filterName="AsynFilter",asyncSupported=true,value={"/ServletAsyn"},dispatcherTypes={DispatcherType.REQUEST,DispatcherType.ASYNC})
public class AsynFilter implements Filter {

    @Override
    public void destroy() {

    }

    @Override
    public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
            throws IOException, ServletException {
        System.out.println("Start.....AsynFilter");
        arg2.doFilter(arg0, arg1);
        System.out.println("End....AsynFilter");
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {

    }

}