The example in this article describes JAVA's method of preventing repeated submission of web forms. Share it with everyone for your reference, the details are as follows:
package cn.com.form;import java.io.IOException;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;//Generate a form public class FormServlet extends HttpServlet { private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Generate random numbers TokenProcessor tp=TokenProcessor.getInstance(); String token=tp.generateToken(); request.getSession().setAttribute("token", token); request.getRequestDispatcher("/form.jsp").forward(request, response) ; } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); }}class TokenProcessor//Token{ /* * 1. Make the constructor private* 2. Create one yourself* 3. Expose a method to the outside world, allowing to obtain the object created above* */ private static final TokenProcessor instance=new TokenProcessor(); private TokenProcessor(){} public static TokenProcessor getInstance() { return instance; } public String generateToken() { String token=System.currentTimeMillis()+new Random().nextInt()+""; try { MessageDigest md=MessageDigest.getInstance("md5"); byte[] md5=md.digest(token.getBytes()); //base64 encoding BASE64Encoder encoder=new BASE64Encoder(); return encoder.encode(md5); } catch (NoSuchAlgorithmException e) { // TODO Auto-generated catch block throw new RuntimeException(e); } }} <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+":/ /"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>My JSP 'form.jsp' starting page</title> <meta http-equiv="pragma " content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv=" keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles .css"> --> </head> <body> <form action="/Session/DoForm" method="post"> <input type="hidden" name="token" value="${token}" > Username: <input type="text" name="userName"> <input type="submit" value="submit"> </form> </body></html> package cn.com.form;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/* * * Servlet implementation class DoForm * Handles form submission requests * */public class DoForm extends HttpServlet { private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { /*String userName=request.getParameter("userName"); try { Thread.sleep(1000*3); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println("Submit registered user to database..."); */ boolean b=isTokenValid(request); if(!b) { System.out.println(" Please do not submit again! "); return; } request.getSession().removeAttribute("token"); System.out.println("Register user to the database =="); } private boolean isTokenValid(HttpServletRequest request) { String client_token=request.getParameter("token"); if(client_token==null) { return false; } String server_token=(String)request.getSession().getAttribute("token"); if(server_token==null) { return false; } if(!client_token.equals(server_token)) { return false; } return true; } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); }}I hope this article will be helpful to everyone in Java web programming.