一、什么是表單重復(fù)提交？
當(dāng)網(wǎng)絡(luò)有延遲時(shí)，用戶提交的表單等數(shù)據(jù)還沒有完成此次提交，但用戶又多次點(diǎn)擊提交，造成用戶數(shù)據(jù)在數(shù)據(jù)庫或存儲中被提交多次。
利用線程延遲，簡單模擬重復(fù)提交。
表單頁面為form.html
[html] view plain copy



form.html

<meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="this is my page"> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->

用戶名 ：

處理提交請求的servlet為DoFormServlet.java
[java] view plain copy
package SessionDemo;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DoFormServlet extends HttpServlet
{

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String username = request.getParameter("username"); //利用線程休眠，模擬網(wǎng)絡(luò)延遲 try { Thread.sleep(1000*3); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("向數(shù)據(jù)庫中注冊數(shù)據(jù)。"); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }

}
在瀏覽器中加載form.html

當(dāng)用戶反復(fù)點(diǎn)擊“提交”時(shí)，就造成了重復(fù)提交。

二、解決方法一：利用javascript阻止
其他不變，將form.html修改為
[html] view plain copy



form.html

<meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="this is my page"> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->

var isCommitted = false;
function dosubmit()
{
if(!isCommitted)
{
isCommitted=true;
return true;
}
else
{
return false;
}
}




用戶名 ：




這樣在瀏覽器中加載form.html后，點(diǎn)擊“提交”，終端中只會輸出一次”向數(shù)據(jù)庫中注冊數(shù)據(jù)。”，表明成功阻止表單反復(fù)提交。
以上form.html可以進(jìn)一步優(yōu)化，當(dāng)用戶點(diǎn)擊“提交”后，“提交”按鈕應(yīng)該變?yōu)榛疑豢捎谩?
[html] view plain copy



form.html

<meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="this is my page"> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->

function dosubmit()
{
var input = document.getElementById("submit");
input.disabled = 'disabled';
return true;
}




用戶名 ：




利用javascript的方法不能完全防止用戶惡意重復(fù)提交，例如：用戶可以將form.html保存后修改，還可以在點(diǎn)擊“提交”后重復(fù)刷新頁面，從而實(shí)現(xiàn)反復(fù)提交。
三、解決方法二：利用服務(wù)器端Session防止表單重復(fù)提交。
其中FormServlet.java為
[java] view plain copy
package SessionDemo;

import java.io.IOException;
import java.io.PrintWriter;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Random;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import sun.misc.BASE64Encoder;

public class FormServlet extends HttpServlet
{

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //產(chǎn)生隨機(jī)數(shù)表單號 TokenProcessor tp = TokenProcessor.getInstance(); String token = tp.generateToken(); request.getSession().setAttribute("token",token); request.getRequestDispatcher("/form.jsp").forward(request, response); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }

}

//設(shè)計(jì)為單例模式
class TokenProcessor
{
private TokenProcessor(){};
private static final TokenProcessor instance = new TokenProcessor();

public static TokenProcessor getInstance() { return instance; } public String generateToken() { //獲得隨機(jī)數(shù)字符串 String token = System.currentTimeMillis() + new Random().nextInt() + ""; //獲得數(shù)據(jù)摘要 try { MessageDigest md = MessageDigest.getInstance("md5"); byte[] md5 = md.digest(token.getBytes()); //利用base64編碼防止亂碼。 BASE64Encoder encoder = new BASE64Encoder(); return encoder.encode(md5); } catch (NoSuchAlgorithmException e) { throw new RuntimeException(e); } }

}
添加form.jsp
[plain] view plain copy
<%@ page language=”java” import=”java.util.*” pageEncoding=”UTF-8”%>

用戶名




將DoFormServlet.java修改為
[java] view plain copy
package SessionDemo;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DoFormServlet extends HttpServlet
{

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String username = request.getParameter("username"); boolean b = isTokenValue(request); if (!b) { System.out.println("請不要重復(fù)提交。"); return; } request.getSession().removeAttribute("token"); System.out.println("向數(shù)據(jù)庫中注冊數(shù)據(jù)。"); } //判斷表單號是否有效 private boolean isTokenValue(HttpServletRequest request) { String clientToken = request.getParameter("token"); if(clientToken==null) { return false; } String serverToken = (String) request.getSession().getAttribute("token"); if(serverToken==null) { return false; } if (!clientToken.equals(serverToken)) { return false; } return true; } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }

}
再瀏覽器中加載FormServlet

點(diǎn)擊“提交”后跳轉(zhuǎn)

終端顯示用戶提交

這時(shí)即使用戶點(diǎn)擊“刷新”，也不能實(shí)現(xiàn)重復(fù)提交。

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