java(16)--利用session防止重复登录操作

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html登录页面
可以采用javascript进行防止重复操作，但是如果用户浏览器禁止js使用，就必须想办法从后台进行防止操作

<!DOCTYPE html><html>  <head>    <title>form.html</title>    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">    <meta http-equiv="description" content="this is my page">    <meta http-equiv="content-type" content="text/html; charset=UTF-8">    <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->    <script type="text/javascript">        var iscommitted=false;        function dosubmit(){        if(!iscommitted){                iscommitted = true;                return true;            }else{                return false;            }        }    </script>  </head>  <body>   <form action="/aDay07/servlet/FormServlet" method="post" onsubmit="return dosubmit()">        用户名：<input type="text" name="username">        <input type="submit" value="提交">    </form>  </body></html>

后台FormServlet

import java.io.IOException;import java.io.PrintWriter;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;import java.util.Random;import java.util.UUID;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import sun.misc.BASE64Encoder;//产生form的servletpublic class FormServlet extends HttpServlet {    public void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        response.setCharacterEncoding("UTF-8");        response.setContentType("text/html;charset=UTF-8");        PrintWriter out = response.getWriter();        String token = TokenProcessor.getInstance().generateToken();        request.getSession().setAttribute("token", token);        request.getRequestDispatcher("/form.jsp").forward(request, response);        /*        out.print("<form action='/aDay07/servlet/DoFormServlet' method='post'>");            out.print("<input type='hidden' name='token' value='"+token+"'>");            out.print("<input type='text' name='username'>");            out.print("<input type='submit' value='提交'>");        out.print("</form>");*/    }    public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        doGet(request, response);    }}//随机数生成器class TokenProcessor{    private TokenProcessor(){};    public static TokenProcessor instance = new TokenProcessor();    public static TokenProcessor getInstance(){        return instance;    }    public String generateToken(){        //return UUID.randomUUID().toString();//简单方法：利用uuid产生唯一随机数        //  3847834873   822382382382738238 828323        String token = System.currentTimeMillis() + new Random().nextInt(1000000) + "";        try {            MessageDigest md = MessageDigest.getInstance("md5");            byte md5[] = md.digest(token.getBytes());  //[99239,23939,]            //base64            BASE64Encoder encoder = new BASE64Encoder();            return encoder.encode(md5);        } catch (NoSuchAlgorithmException e) {            throw new RuntimeException(e);        }    }}

form.jsp页面
将token传输到客户端，以便之后用来校验

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>My JSP 'form.jsp' starting page</title>  </head>    <body>       <form action="/aDay07/servlet/DoFormServlet" method="post">        <input type="hidden" name="token" value="<%=session.getAttribute("token") %>">        用户名：<input type="text" name="username">        <input type="submit" value="提交">    </form>     </body></html>

DoFormServlet页面

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 DoFormServlet extends HttpServlet {    public void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        boolean b = isTokenValid(request);        if (!b) {            System.out.println("你是重复提交！！");            return;        }        request.getSession().removeAttribute("token");        System.out.println("处理提交！！！");    }    // 判断表单是否为重复提交    private boolean isTokenValid(HttpServletRequest request) {        String c_token = request.getParameter("token");        if (c_token == null) {            return false;        }        String s_token = (String) request.getSession().getAttribute("token");        if (s_token == null) {            return false;        }        if (!c_token.equals(s_token)) {            return false;        }        return true;    }    public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        doGet(request, response);    }}

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