Servlet3.0提供异步处理
在以前的Servlet规范化，如果Servlet作为控制器调用了一个耗时的业务方法，那么必须等到业务方法完全返回之后才能生成响应，这将使用Servlet对业务方法的调用变成一种阻塞式的调用，因此效率比较低。
Servlet3.0规范引入了异步处理来解决这个问题，异步处理允许Servlet重新发起一条新线程去调用 耗时业务方法，这样就可以避免等待。
Servlet3.0的异步处理是通过AsyncContext类来处理的，Servlet可通过ServletRequest的如下两个方法开启异步调用，创建AsyncContext对象：
AsyncContext startAsync()
AsyncContext startAsync(ServletRequest,ServletResponse)
异步处理类AsyncServlet.java
package aniyo.servlet.async;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
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;
/**
* Servlet 3.0提供的异步处理
* 异步操作通过AsyncContext类来处理，通过startAsync()方法来开启异步调用
* @author aniyo
* blog:http://aniyo.iteye.com
*
*/
@WebServlet(name="asyncServle",urlPatterns="/asyncServlet",asyncSupported=true)
public class AsyncServlet extends HttpServlet {
/* (non-Javadoc)
* @see javax.servlet.http.HttpServlet#doGet(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=GBK");
PrintWriter out = response.getWriter();
out.println("<title>异步调用示例</title>");
out.println("进入Servlet的时间："+new Date()+".<br/>");
out.flush();
//创建AsyncContext，开始异步调用
AsyncContext actx = request.startAsync();
//设置异步调用的超时时长
actx.setTimeout(30*1000);
//启动异步调用的线程
actx.start(new Executor(actx));
out.println("结束Servlet的时间："+new Date()+".<br/>");
out.flush();
}
}
线程类Executor.java
package aniyo.servlet.async;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.AsyncContext;
import javax.servlet.ServletRequest;
public class Executor implements Runnable{
private AsyncContext actx = null;
public Executor(AsyncContext actx) {
this.actx = actx;
}
/* (non-Javadoc)
* @see java.lang.Runnable#run()
*/
@Override
public void run() {
//等待5秒
try {
Thread.sleep(5*1000);
ServletRequest request = actx.getRequest();
List<String> books = new ArrayList<String>();
books.add("java");
books.add("oracle");
books.add("j2ee");
request.setAttribute("books", books);
actx.dispatch("/async.jsp");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}async.jsp
<%@page import="java.util.Date"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8" session="false"%>
<%@ taglib prefix = "c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<ul>
<c:forEach items="${books}" var="book">
<li>
${book }
</li>
</c:forEach>
</ul>
<%out.println("业务调用结束的时间："+ new Date());
//完成异步调用
//request.getAsyncContext().complete();
%>
</body>
</html>
