1). 重复提交的情况:
①. 在表单提交到一个 Servlet, 而 Servlet 又通过请求转发的方式响应一个 JSP(HTML) 页面,
此时地址栏还保留着 Serlvet 的那个路径, 在响应页面点击 "刷新"
②. 在响应页面没有到达时重复点击 "提交按钮".
③. 点击 "返回", 再点击 "提交"
2). 不是重复提交的情况:
点击 "返回", "刷新" 原表单页面, 再 "提交"。
3). 如何避免表单的重复提交:
在表单中做一个标记, 提交到 Servlet 时, 检查标记是否存在且是否和预定义的标记一致, 若一致, 则受理请求,
并销毁标记, 若不一致或没有标记, 则直接响应提示信息: "重复提交"
①.调用 RequestDispatcher.forward() 方法,浏览器所保留的URL 是先前的表单提交的 URL,此时点击”刷新”, 浏览器将再次提交用户先前输入的数据,引起重复提交;如果采用 HttpServletResponse.sendRedirct() 方法将客户端重定向到成功页面,将不会出现重复提交问题
②.利用Session对表单进行token标识
- 在原表单页面, 生成一个随机值 token
- 在原表单页面, 把 token 值放入 session 属性中
- 在原表单页面, 把 token 值放入到 隐藏域 中.
- 在目标的 Servlet 中: 获取 session 和 隐藏域 中的 token 值
- 比较两个值是否一致: 若一致, 受理请求, 且把 session 域中的 token 属性清除
- 若不一致, 则直接响应提示页面: "重复提交"
表单页面
<%@ page import="java.util.Date" %> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <% //随机生成一个标识 String tokenValue = new Date().getTime()+""; session.setAttribute("token",tokenValue); %> <form action="<%=request.getContextPath()%>/tokenServlet" method="post"> <input type="hidden" name="tokenValue" value=<%=tokenValue%> /> Username:<input type="text" name="username"/> <input type="submit" value="登录"/> </form> </body> </html>
TokenServlet.java
package yang.mybatis.servlet.token; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import java.io.IOException; /** * Created by yangshijing on 2017/11/22 0022. */ public class TokenServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //模仿后台延时 try { Thread.sleep(300); } catch (InterruptedException e) { e.printStackTrace(); } HttpSession session = request.getSession(); //从Session域中获得标识 String token = (String)session.getAttribute("token"); //从表单隐藏域中获取token value String tokenValue = request.getParameter("tokenValue"); //如果标识不为空且隐藏域中值和Session域中的值一致,则处理该表单请求 if(token != null && tokenValue.equals(token)){ session.removeAttribute("token"); }else{ response.sendRedirect(request.getContextPath()+"/jsp/token/token.jsp"); return; } request.getRequestDispatcher("/jsp/token/success.jsp").forward(request,response); } }
TokenProcessor.java
用于管理表单标识号的工具类,它主要用于产生、比较和清除存储在当前用户Session中的表单标识号。为了保证表单标识号的唯一性,每次将当前SessionID和系统时间的组合值按MD5算法计算的结果作为表单标识号,并且将TokenProcessor类设计为单例类
package yang.mybatis.servlet.token; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpSession; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; /** * Created by yangshijing on 2017/11/23 0023. */ public class TokenProcessor { //表单隐藏域的name属性值 private static final String TOKEN_KEY = "TOKEN_KEY"; //Session域中的属性值 private static final String TRANSACTION_TOKEN_KEY = "TRANSACTION_TOKEN_KEY"; private static TokenProcessor instance = new TokenProcessor(); private long previous; protected TokenProcessor() { super(); } //单例模式 public static TokenProcessor getInstance() { return instance; } //判断表单提交请求是否重复 public synchronized boolean isTokenValid(HttpServletRequest request) { HttpSession session = request.getSession(false); if (session == null) { return false; } //从Session域中获取标识值 String saved = (String) session.getAttribute(TRANSACTION_TOKEN_KEY); if (saved == null) { return false; } String token = request.getParameter(TOKEN_KEY); if (token == null) { return false; } return saved.equals(token); } //移除Session域中的token public synchronized void resetToken(HttpServletRequest request) { HttpSession session = request.getSession(false); if (session == null) { return; } session.removeAttribute(TRANSACTION_TOKEN_KEY); } //将token保存到Session域中并返回token public synchronized String saveToken(HttpServletRequest request) { HttpSession session = request.getSession(); String token = generateToken(request); if (token != null) { session.setAttribute(TRANSACTION_TOKEN_KEY, token); } return token; } public synchronized String generateToken(HttpServletRequest request) { HttpSession session = request.getSession(); return generateToken(session.getId()); } public synchronized String generateToken(String id) { try { long current = System.currentTimeMillis(); if (current == previous) { current++; } previous = current; byte[] now = new Long(current).toString().getBytes(); MessageDigest md = MessageDigest.getInstance("MD5"); md.update(id.getBytes()); md.update(now); return toHex(md.digest()); } catch (NoSuchAlgorithmException e) { return null; } } private String toHex(byte[] buffer) { StringBuffer sb = new StringBuffer(buffer.length * 2); for (int i = 0; i < buffer.length; i++) { sb.append(Character.forDigit((buffer[i] & 0xf0) >> 4, 16)); sb.append(Character.forDigit(buffer[i] & 0x0f, 16)); } return sb.toString(); } }
重构的index.jsp
<%@ page import="java.util.Date" %> <%@ page import="yang.mybatis.servlet.token.TokenProcessor" %> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <%--<% String tokenValue = new Date().getTime()+""; session.setAttribute("token",tokenValue); %>--%> <form action="<%=request.getContextPath()%>/tokenServlet" method="post"> <input type="hidden" name="TOKEN_KEY" value=<%=TokenProcessor.getInstance().saveToken(request)%> /> Username:<input type="text" name="username"/> <input type="submit" value="登录"/> </form> </body> </html>
重构的TokenServlet
package yang.mybatis.servlet.token; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import java.io.IOException; /** * Created by yangshijing on 2017/11/22 0022. */ public class TokenServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //模仿后台延时 try { Thread.sleep(300); } catch (InterruptedException e) { e.printStackTrace(); } /* HttpSession session = request.getSession(); //从Session域中获得标识 String token = (String)session.getAttribute("token"); //从表单隐藏域中获取token value String tokenValue = request.getParameter("tokenValue"); //如果标识不为空且隐藏域中值和Session域中的值一致,则处理该表单请求 if(token != null && tokenValue.equals(token)){ session.removeAttribute("token"); }else{ response.sendRedirect(request.getContextPath()+"/jsp/token/token.jsp"); return; } request.getRequestDispatcher("/jsp/token/success.jsp").forward(request,response);*/ boolean tokenValid = TokenProcessor.getInstance().isTokenValid(request); //如果不是重复的表单请求,移除token并处理请求 if(tokenValid){ TokenProcessor.getInstance().resetToken(request); }else { //重复的表单请求,结束方法,并重定向到提示页面 response.sendRedirect(request.getContextPath()+"/jsp/token/token.jsp"); return; } response.sendRedirect(request.getContextPath()+"/jsp/token/success.jsp"); } }
时间: 2024-10-05 05:06:54