利用session防止表单重复提交

l表单页面由servlet程序生成，servlet为每次产生的表单页面分配一个唯一的随机标识号，并在FORM表单的一个隐藏字段中设置这个标识号，同时在当前用户的Session域中保存这个标识号。
l当用户提交FORM表单时，负责处理表单提交的serlvet得到表单提交的标识号，并与session中存储的标识号比较，如果相同则处理表单提交，处理完后清除当前用户的Session域中存储的标识号。
l在下列情况下，服务器程序将拒绝用户提交的表单请求：
ü存储Session域中的表单标识号与表单提交的标识号不同
ü当前用户的Session中不存在表单标识号
ü用户提交的表单数据中没有标识号字段
l

l编写工具类生成表单标识号：TokenProcessor
l

package com.csdn.session;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

import java.util.Random;

import sun.misc.BASE64Encoder;

public class TokenProcessor {

private TokenProcessor(){

}

private static final TokenProcessor instance = new TokenProcessor();

public static TokenProcessor getInstance(){

return instance;

}

public String generateToken(){

int i = new Random().nextInt();

String token = System.currentTimeMillis()+i+"";

try {

MessageDigest md = MessageDigest.getInstance("md5");

byte[] md5 = md.digest(token.getBytes());

BASE64Encoder encode = new BASE64Encoder();

return encode.encode(md5);

} catch (NoSuchAlgorithmException e) {

// TODO Auto-generated catch block

throw new RuntimeException(e);

}

}

}

package com.csdn.session;

import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class FormGenerateServlet extends HttpServlet {

/**

*

*/

private static final long serialVersionUID = 1L;

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html;charset=UTF-8");

PrintWriter out = response.getWriter();

TokenProcessor tp = TokenProcessor.getInstance();

String token = tp.generateToken();

request.getSession().setAttribute("token", token);

out.print("<form action='FormDealServlet' method='post' >");

out.print("<input type='hidden' name='token' value='" + token + "'/>");

out.print("用户名：<input type='text' name='usename' />");

out.print("<input type='submit' value='提交' />");

out.print("</form>");

}

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

doGet(request, response);

}

}

package com.csdn.session;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.swing.JOptionPane;

public class FormDealServlet extends HttpServlet {

/**

*

*/

private static final long serialVersionUID = 1L;

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

request.setCharacterEncoding("UTF-8");

boolean b = isFlag(request);

if(!b){

System.out.println("请不要重复提交表单");

return;

}

request.getSession().removeAttribute("token");

System.out.println("更新数据库的用户的信息");

}

public boolean isFlag(HttpServletRequest request){

String client_token = request.getParameter("token");

if(client_token==null){

return false;

}

String server_token = (String) request.getSession().getAttribute("token");

if(server_token==null){

return false;

}

if(!client_token.equals(server_token)){

return false;

}

return true;

}

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

doGet(request, response);

}

}