JavaWeb中HttpSession中表单的重复提交示例

时间:2017-06-02 23:41 来源:武松娱乐整理 字体:[ ] 评论:
表单的重复提交
  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了一个 JSP(HTML)页面,此时地址栏还保留着 Servlet 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
  1. 不是重复提交的情况:点击 “返回”,“刷新” 原表单页面,再点击提交。
  2. 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和预定义的标记一样,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仅提供一个隐藏域不行:<input type="hidden" name="token" value="lsy"> ②把标记放在 Request 中 , 行不通,表单页面刷新后,request 已经被销毁,再提交表单是一个新的 request 的。 ③把标记放在 Session 中,可以 1. 在原表单页面,生成一个随机值 token
2. 在原表单页面,把 token 值放入 session 属性中
3. 在原表单页面,把 token 值放入到隐藏域 4. 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,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” 我们可以通过 Struts1 中写好的类 TokenProcessor 来重构代码, 面向组件编程
package com.lsy.javaweb; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpSession; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; public class TokenProcessor { private static final String TOKEN_KEY = "TOKEN_KEY"; private static final String TRANSACTION_TOKEN_KEY = "TRANSACTION_TOKEN_KEY"; /** * The singleton instance of this class. */ private static TokenProcessor instance = new TokenProcessor(); /** * The timestamp used most recently to generate a token value. */ private long previous; /** * Protected constructor for TokenProcessor. Use * TokenProcessor.getInstance() to obtain a reference to the processor. */ protected TokenProcessor() { super(); } /** * Retrieves the singleton instance of this class. */ public static TokenProcessor getInstance() { return instance; } /** * <p> * Return <code>true</code> if there is a transaction token stored in the * user's current session, and the value submitted as a request parameter * with this action matches it. Returns <code>false</code> under any of the * following circumstances: * </p> * * <ul> * * <li>No session associated with this request</li> * * <li>No transaction token saved in the session</li> * * <li>No transaction token included as a request parameter</li> * * <li>The included transaction token value does not match the transaction * token in the user's session</li> * * </ul> * * @param request * The servlet request we are processing */ public synchronized boolean isTokenValid(HttpServletRequest request) { return this.isTokenValid(request, false); } /** * Return <code>true</code> if there is a transaction token stored in the * user's current session, and the value submitted as a request parameter * with this action matches it. Returns <code>false</code> * * <ul> * * <li>No session associated with this request</li> * <li>No transaction token saved in the session</li> * * <li>No transaction token included as a request parameter</li> * * <li>The included transaction token value does not match the transaction * token in the user's session</li> * * </ul> * * @param request * The servlet request we are processing * @param reset * Should we reset the token after checking it? */ public synchronized boolean isTokenValid(HttpServletRequest request, boolean reset) { // Retrieve the current session for this request HttpSession session = request.getSession(false); if (session == null) { return false; } // Retrieve the transaction token from this session, and // reset it if requested String saved = (String) session.getAttribute(TRANSACTION_TOKEN_KEY); if (saved == null) { return false; } if (reset) { this.resetToken(request); } // Retrieve the transaction token included in this request String token = request.getParameter(TOKEN_KEY); if (token == null) { return false; } return saved.equals(token); } /** * Reset the saved transaction token in the user's session. This indicates * that transactional token checking will not be needed on the next request * that is submitted. * * @param request * The servlet request we are processing */ public synchronized void resetToken(HttpServletRequest request) { HttpSession session = request.getSession(false); if (session == null) { return; } session.removeAttribute(TRANSACTION_TOKEN_KEY); } /** * Save a new transaction token in the user's current session, creating a * new session if necessary. * * @param request * The servlet request we are processing */ 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; } /** * Generate a new transaction token, to be used for enforcing a single * request for a particular transaction. * * @param request * The request we are processing */ public synchronized String generateToken(HttpServletRequest request) { HttpSession session = request.getSession(); return generateToken(session.getId()); } /** * Generate a new transaction token, to be used for enforcing a single * request for a particular transaction. * * @param id * a unique Identifier for the session or other context in which * this token is to be used. */ 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; } } /** * Convert a byte array to a String of hexadecimal digits and return it. * * @param buffer * The byte array to be converted */ 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(); } }
以上所述是小编给大家介绍的JavaWeb中HttpSession中表单的重复提交示例,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对武松娱乐网站的支持!
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