sesion防止表单重复提交（2）

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利用md5算法得到数据的指纹，再利用baset64算法获取计算后的字符串

package com.jingtian.others;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;import sun.misc.BASE64Encoder;public class Md5Test {public static void main(String[] args) {String str = "景天晓志";try {//得到MD5算法的MessageDigest   //对数据进行处理，得到处理后的字节//得到baset64算法的对象//对用MD5处理后的数据进行计算，得到处理后的字符串MessageDigest dm = MessageDigest.getInstance("md5");byte[] md5 = dm.digest(str.getBytes());BASE64Encoder encoder = new BASE64Encoder();String baset64 = encoder.encode(md5);System.out.println(baset64);//h52DUtauqHMMa5c0Bn53Iw==} catch (NoSuchAlgorithmException e) {throw new RuntimeException(e);}}}

session防止表单重复提交

手机令牌:本质就是生成一个随机数保存在session里面，用户看不到，通过比较用户的随机数和服务器从session里面得到的随机数是否相等。刷新的时候已经删除。。

用户没带数据就是有人再干坏事
服务器这边找不到就是闲着没个鸟事干刷新，
两边数据必须相等。。

生成一个随机数
base64编码
这里利用单例设计模式
1.构建一个私有构造方法
2.新建一个私有静态final对象
3.对外暴露一个方法

md5加密
base64翻译成明文：传电影

先访问FormServlet生成令牌，自动跳转首页jsp，jsp交给DoFormServlet处理

package com.jingtian.sessionForm;import java.io.IOException;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;import java.util.Random;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import sun.misc.BASE64Encoder;public class FormServlet extends HttpServlet {/** * 写给浏览器一个表单，并且防止多次重复提交而创建随机数 */private static final long serialVersionUID = 1L;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {// 产生随机数（表单号 ）TokenProcessor tp = TokenProcessor.getInstance();String token = tp.generateToken();request.getSession().setAttribute("token", token);request.getRequestDispatcher("/form.jsp").forward(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}class TokenProcessor {// 令牌发生器/** * 1.把构造方法私有  * 2.新建一个私有静态final对象 * 3.对外暴露一个方法，允许获得创建的对象 */private TokenProcessor() {}private static final TokenProcessor instance = new TokenProcessor();public static TokenProcessor getInstance() {return instance;}public String generateToken() {// 获取唯一的表单码String token = System.currentTimeMillis() + new Random().nextInt() + "";try {MessageDigest md5 = MessageDigest.getInstance("md5");byte[] md = md5.digest(token.getBytes());BASE64Encoder encoder = new BASE64Encoder();return encoder.encode(md);} catch (NoSuchAlgorithmException e) {throw new RuntimeException(e);}}}

再就是那个jsp页面

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"%><!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><form action="${pageContext.request.contextPath}/servlet/DoFormServlet" method="post"><input type="hidden" name="token" value="${token}">用户名:<input type="text" name="username"><br/><input type="submit" value="提交"></form></body></html>

最后就是那个处理提交请求的servlet

package com.jingtian.sessionForm;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 DoFormServlet extends HttpServlet {/** * 处理表单的重复提交 */private static final long serialVersionUID = 1L;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {boolean b = isTokenValue(request);if (!b) {System.out.println("请不要重复提交");return;}request.getSession(false).removeAttribute("token");System.out.println("向数据库中注入数据");}private boolean isTokenValue(HttpServletRequest request) {String client_token = request.getParameter("token");if (client_token == null) {return false;}String server_token = (String) request.getSession(false).getAttribute("token");if (server_token == null) {return false;}if (!server_token.equals(client_token)) {return false;}return true;}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}