jsp表單重複提交

1.重複提交的情況:

①. 在表單提交到一個 Servlet, 而 Servlet 又通過請求轉發的方式響應一個 JSP(HTML) 頁面,
此時地址欄還保留着 Serlvet 的那個路徑, 在響應頁面點擊 "刷新"

②. 在響應頁面沒有到達時重複點擊 "提交按鈕".

③. 點擊 "返回", 再點擊 "提交"

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	<form action="<%=request.getContextPath()%>/tokenServlet" method="post">
		<input type="text" name="name"> <input type="submit">
	</form>
</body>
</html>

public class TokenServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		try {
			Thread.currentThread().sleep(3000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		String name = request.getParameter("name");

		// 訪問數據庫服務器
		System.out.println("name :" + name);
		// request.getRequestDispatcher("/token/success.jsp").forward(request,
		// response); // 轉發
		// "/"代表WEB項目根目錄

		response.sendRedirect(request.getContextPath() + "/token/success.jsp"); // 重定向
																				// “/”
																				// 代表
																				// WEB站點根目錄

	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

2. 不是重複提交的情況: 點擊 "返回", "刷新" 原表單頁面, 再 "提交"。

3. 如何避免表單的重複提交: 在表單中做一個標記, 提交到 Servlet 時, 檢查標記是否存在且是否和預定義的標記一致, 若一致, 則受理請求,
並銷燬標記, 若不一致或沒有標記, 則直接響應提示信息: "重複提交"

方法

把標記放在 session 中

在原表單頁面, 生成一個隨機值 token
> 在原表單頁面, 把 token 值放入 session 屬性中
> 在原表單頁面, 把 token 值放入到隱藏域中.

> 在目標的 Servlet 中: 獲取 session 和隱藏域中的 token 值
> 比較兩個值是否一致: 若一致, 受理請求, 且把 session 域中的 token 屬性清除
> 若不一致, 則直接響應提示頁面: "重複提交"

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<%@page import="java.util.Date"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	<%
		String tokenValue = new Date().getTime() + "";
		session.setAttribute("token", tokenValue);
	%>
	<form action="<%=request.getContextPath()%>/tokenServlet" method="post">
		<input type="hidden" name="token" value="<%=tokenValue%>"> <input
			type="text" name="name"> <input type="submit">
	</form>
</body>
</html>

protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		try {
			Thread.currentThread().sleep(3000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

		HttpSession session = request.getSession();
		Object token = session.getAttribute("token");
		String tokenValue = request.getParameter("token");
		System.out.println(token);
		System.out.println(tokenValue);

		if (token != null && token.equals(tokenValue)) {
			session.removeAttribute("token");
		} else {
			response.sendRedirect(request.getContextPath() + "/token/token.jsp");
			return;
		}

		String name = request.getParameter("name");

		// 訪問數據庫服務器
		System.out.println("name :" + name);
		// request.getRequestDispatcher("/token/success.jsp").forward(request,
		// response); // 轉發
		// "/"代表WEB項目根目錄

		response.sendRedirect(request.getContextPath() + "/token/success.jsp"); // 重定向
																				// “/”
																				// 代表
																				// WEB站點根目錄

	}

使用TokenProcessor 工具類

package com.token;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class TokenProcessor {

	public static final String TOKEN_KEY = "TOKEN_KEY";

	private static final String TRANSACTION_TOKEN_KEY = "TRANSACTION_TOKEN_KEY";

	private static TokenProcessor instance = new TokenProcessor();

	private long previous;

	protected TokenProcessor() {
		super();
	}

	public static TokenProcessor getInstance() {
		return instance;
	}

	public synchronized boolean isTokenValid(HttpServletRequest request) {
		return this.isTokenValid(request, false);
	}

	public synchronized boolean isTokenValid(HttpServletRequest request, boolean reset) {
		HttpSession session = request.getSession(false);

		if (session == null) {
			return false;
		}

		String saved = (String) session.getAttribute(TRANSACTION_TOKEN_KEY);

		if (saved == null) {
			return false;
		}

		if (reset) {
			this.resetToken(request);
		}

		String token = request.getParameter(TOKEN_KEY);

		if (token == null) {
			return false;
		}

		return saved.equals(token);
	}

	public synchronized void resetToken(HttpServletRequest request) {
		HttpSession session = request.getSession(false);

		if (session == null) {
			return;
		}

		session.removeAttribute(TRANSACTION_TOKEN_KEY);
	}

	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();
	}
}

修改代碼

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<%@page import="java.util.Date"%>
<%@page import="com.token.TokenProcessor"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	<%-- 	<%
		String tokenValue = new Date().getTime() + "";
		session.setAttribute("token", tokenValue);
	%> --%>
	<%
		
	%>
	<form action="<%=request.getContextPath()%>/tokenServlet" method="post">
		<input type="hidden" name="<%=TokenProcessor.TOKEN_KEY%>"
			value="<%=TokenProcessor.getInstance().generateToken(request)%>">
		<input type="text" name="name"> <input type="submit">
	</form>
</body>
</html>

protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		try {
			Thread.currentThread().sleep(3000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

		// HttpSession session = request.getSession();
		// Object token = session.getAttribute("token");
		// String tokenValue = request.getParameter("token");
		// System.out.println(token);
		// System.out.println(tokenValue);
		//
		// if (token != null && token.equals(tokenValue)) {
		// session.removeAttribute("token");
		// } else {
		// response.sendRedirect(request.getContextPath() + "/token/token.jsp");
		// return;
		// }

		boolean tokenValid = TokenProcessor.getInstance().isTokenValid(request);
		if (tokenValid) {
			TokenProcessor.getInstance().resetToken(request);
		} else {
			response.sendRedirect(request.getContextPath() + "/token/token.jsp");
			return;
		}

		String name = request.getParameter("name");
		// 訪問數據庫服務器
		System.out.println("name :" + name);
		// request.getRequestDispatcher("/token/success.jsp").forward(request,
		// response); // 轉發
		// "/"代表WEB項目根目錄

		response.sendRedirect(request.getContextPath() + "/token/success.jsp"); // 重定向
																				// “/”
																				// 代表
																				// WEB站點根目錄

	}

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