实验：使用session完成防止表单重复提交：当提供表单页面时，在表单中隐藏一个随机数值，并且将该随机数保存到session中，当表单提交时，检查提交上来到随机数与session中的随机数是否相同，如果相同则允许注册，注册后立即删除session中的随机数，如果不同则认为是表单的重复提交。
实验：实现购买与付账的功能
1.建立一个jsp实现到BuyServlet&PayServlet的超链接并带一个参数过来
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title></title>
<meta http-equiv=" pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
</head>
<body>
<a href="<%=request.getContextPath()%>/servlet/BuyServlet?prod=冰箱">购买冰箱</a>
<a href="<%=request.getContextPath()%>/servlet/BuyServlet?prod=空调">购买空调</a>
<a href="<%=request.getContextPath()%>/servlet/PayServlet">付账</a>
</body>
</html>
运行界面:
2.在BuyServlet实现通过request.getParamer()的方式获取参数，然后将这个参数设置到session域对象中。下面的设置Cookie的代码是为了实现即时关闭了浏览器（默认是浏览器关闭，cookie死亡，即session丢失）也可以向浏览器写数据。从而关闭了浏览器也可以实现付款(知道是买的那个不会报NULl)
package cn.itheima.session;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class BuyServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//解决中文乱码问题get提交方式
//1.获取参数
String prod=request.getParameter("prod");
prod = new String(prod.getBytes("iso8859-1"),"utf-8");
//2.放到session域中
HttpSession session = request.getSession();
session.setAttribute("prod", prod);
//3.重写Cookie重新设置JSESSIONID的声明周期
Cookie c=new Cookie("JSESSIONID", session.getId());
c.setPath(request.getContextPath());
c.setMaxAge(1800);
response.addCookie(c);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
点击购买
package cn.itheima.session;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class PayServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
//1.获取session
String prod = (String) request.getSession().getAttribute("prod");
response.getWriter().write("您购买的是价值9999元的"+prod);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
运行结果:
大家可以尝试关闭浏览器....也能实现付款的功能！
黑马day05 session&重新设置JSESSIONID的生命周期
原文：http://blog.csdn.net/u014010769/article/details/46564829
