表单的重复提交
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呐喊教程网站的支持！
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