表单重复提交问题
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一、常见的重复提交问题
a>点击提交按钮两次。
b>点击刷新按钮。
c>使用浏览器后退按钮重复之前的操作，导致重复提交表单。
d>使用浏览器历史记录重复提交表单。
e>浏览器重复的HTTP请求。
二、防止表单重复提交原理
提交表单的时候提交一份随机的字符串或随机数字等等，再把这个随机的数据存到request里面，然后把表单数据提交，在后台验证的时候判断提交的这两份额外的数据是否一致，如果一致，则把其中一份删除掉，这么做的目的是防止再次提交，继续进行操作，如果不一致，则返回一个响应的页面进行提示！
三、代码
项目目录
login.jsp
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> 2 <% 3 String path = request.getContextPath(); 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 5 %> 6 7 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 8 <html> 9 <head> 10 <base href="<%=basePath%>"> 11 12 <title>表单重复提交问题</title> 13 <meta http-equiv="pragma" content="no-cache"> 14 <meta http-equiv="cache-control" content="no-cache"> 15 <meta http-equiv="expires" content="0"> 16 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> 17 <meta http-equiv="description" content="This is my page"> 18 <!-- 19 <link rel="stylesheet" type="text/css" href="styles.css"> 20 --> 21 <% 22 String tokenValue = new Date().getTime() + ""; 23 %> 24 </head> 25 26 <body> 27 表单重复提交问题<hr> 28 <form action="<%=path %>/tokenServlet" method="post"> 29 username :<input type="text" name="username" /><br> 30 password :<input type="password" type="password" size="20"/><br> 31 32 <input type="hidden" name="token" value="<%=tokenValue%>" /> 33 <% 34 session.setAttribute("token", tokenValue); 35 %> 36 37 <input type="submit" value="登录"> 38 </form> 39 </body> 40 </html>
success.jsp
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> 2 <% 3 String path = request.getContextPath(); 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 5 %> 6 7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 8 <html> 9 <head> 10 <base href="<%=basePath%>"> 11 12 <title>My JSP \'index.jsp\' starting page</title> 13 <meta http-equiv="pragma" content="no-cache"> 14 <meta http-equiv="cache-control" content="no-cache"> 15 <meta http-equiv="expires" content="0"> 16 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> 17 <meta http-equiv="description" content="This is my page"> 18 <!-- 19 <link rel="stylesheet" type="text/css" href="styles.css"> 20 --> 21 </head> 22 23 <body> 24 登陆成功，欢迎您，<%=request.getAttribute("username") %> 25 </body> 26 </html>
token.jsp
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> 2 <% 3 String path = request.getContextPath(); 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 5 %> 6 7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 8 <html> 9 <head> 10 <base href="<%=basePath%>"> 11 12 <title>My JSP \'index.jsp\' starting page</title> 13 <meta http-equiv="pragma" content="no-cache"> 14 <meta http-equiv="cache-control" content="no-cache"> 15 <meta http-equiv="expires" content="0"> 16 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> 17 <meta http-equiv="description" content="This is my page"> 18 <!-- 19 <link rel="stylesheet" type="text/css" href="styles.css"> 20 --> 21 </head> 22 23 <body> 24 请不要重复提交表单数据!<br> 25 </body> 26 </html>
TokenServlet.java
1 package com.xjh.form; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 6 import javax.servlet.ServletException; 7 import javax.servlet.http.HttpServlet; 8 import javax.servlet.http.HttpServletRequest; 9 import javax.servlet.http.HttpServletResponse; 10 import javax.servlet.http.HttpSession; 11 12 public class TokenServlet extends HttpServlet { 13 14 public void doGet(HttpServletRequest request, HttpServletResponse response) 15 throws ServletException, IOException { 16 doPost(request, response); 17 } 18 19 public void doPost(HttpServletRequest request, HttpServletResponse response) 20 throws ServletException, IOException { 21 HttpSession session = request.getSession(); 22 Object token = session.getAttribute("token"); //session中的token 23 String tokenValue = request.getParameter("token"); //表单提交的隐藏数据token 24 System.out.println(token); //第二次进来的时候这个会输出null 25 System.out.println(tokenValue); 26 27 if(token != null && token.equals(tokenValue)){ //第一次进来符合，把数据移除，第二次进来不符合 28 session.removeAttribute("token"); 29 }else { 30 response.sendRedirect(request.getContextPath() + "/token/token.jsp"); //请求转发 31 return ; 32 } 33 34 String username = request.getParameter("username"); 35 request.setAttribute("username", username); 36 System.out.println("username = " + username); 37 request.getRequestDispatcher("/token/success.jsp").forward(request, response); //请求转发 38 39 // response.sendRedirect(request.getContextPath() + "/token/success.jsp"); //请求重定向 40 } 41 }
访问：http://127.0.0.1:8080/demo-form/tokenServlet
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