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JavaWeb中HttpSession中表单的重复提交示例

表单的重复提交

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  • 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

  • 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。
  • 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:

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;
  }
  /**
   * 

* Return true 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 false under any of the * following circumstances: *

* *
    * *
  • No session associated with this request
  • * *
  • No transaction token saved in the session
  • * *
  • No transaction token included as a request parameter
  • * *
  • The included transaction token value does not match the transaction * token in the user's session
  • * *
* * @param request * The servlet request we are processing */ public synchronized boolean isTokenValid(HttpServletRequest request) { return this.isTokenValid(request, false); } /** * Return true 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 false * *
    * *
  • No session associated with this request
  • *
  • No transaction token saved in the session
  • * *
  • No transaction token included as a request parameter
  • * *
  • The included transaction token value does not match the transaction * token in the user's session
  • * *
* * @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创新互联网站的支持!


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