理解并掌握Cookie的作用以及利用cookie實現用戶的自動登錄功能，實現下圖效果
當服務器判斷出該用戶是首次登錄的時候，會自動跳轉到登錄界面等待用戶登錄，并填入相關信息。通過設置Cookie的有效期限來保存用戶的信息，關閉瀏覽器后，驗證是否能夠自動登錄，若能登錄，則打印歡迎信息；否則跳轉到登錄頁面。
login.jsp
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><%request.setCharacterEncoding("GB2312"); %><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>" rel="external nofollow" rel="external nofollow" > <title>My JSP 'login.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" rel="external nofollow" rel="external nofollow" > --> <script type="text/javascript"> window.onload = function(){ //獲取submit var submit = document.getElementById("submit"); var name = document.getElementById("name"); //為submit綁定單擊響應函數 submit.onclick = function(){ times = document.getElementsByName("time"); var count=0; for(var i=0;i<times.length;i++){ if(times[i].checked == true){ count++; } } if(count>=2){ alert("只能選擇一個選項"); return false; } }; }; </script> </head> <body> <!-- 設置html頁面 --> <form action="sucess.jsp" method="post"> 用戶名：<input name="username" /><br/> <input type="checkbox" name="time" value="notSave" />不保存 <input type="checkbox" name="time" value="aDay" />一天 <input type="checkbox" name="time" value="aWeek" />一周 <input type="checkbox" name="time" value="forever" />永久 <br/><br/> <input type="submit" name="submit" id="submit" value="登錄"/> </form> <% //讀取session值 String val= (String)session.getAttribute("name"); //如果session不存在 if(val==null){ val ="不存在"; } out.print("當前/""+val+"/"用戶可自動登錄"); %> </body></html>sucess.jsp
%@ 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%>" rel="external nofollow" rel="external nofollow" > <title>My JSP 'show.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" rel="external nofollow" rel="external nofollow" > --> </head> <body> <% //獲取username String name = request.getParameter("username"); //判斷用戶名是否存在 if(name != null && !name.trim().equals("")){ String[] time = request.getParameterValues("time"); //設置session值，便于login頁面讀取 session.setAttribute("name", name); //設置Cookie Cookie Cookie = new Cookie("name",name); //根據提交選項設置cookie保存時間 if(time != null){ for(int i=0;i<time.length;i++){ //不保存Cookie if(time[i].equals("notSave")){ Cookie.setMaxAge(0); } //保存一天Cookie if(time[i].equals("aDay")){ Cookie.setMaxAge(60*60*24); } //保存一周Cookie if(time[i].equals("aWeek")){ Cookie.setMaxAge(60*60*24*7); } //永久保存Cookie，設置為100年 if(time[i].equals("forever")){ Cookie.setMaxAge(60*60*24*365*100); } } } //在客戶端保存Cookie response.addCookie(Cookie); } else{%> <%--用戶名不存在則進行判斷是否已有cookie --%> <% //獲取cookie Cookie[] cookies = request.getCookies(); //cookie存在 if(cookies != null && cookies.length > 0){ for(Cookie cookie:cookies){ //獲取cookie的名字 String cookieName = cookie.getName(); //判斷是否與name相等 if(cookieName.equals("name")){ //獲取cookie的值 String value = cookie.getValue(); name = value; } } } } if(name != null && !name.trim().equals("")){ out.print("您好: " + name+"歡迎登錄"); } else{//否則重定向到登錄界面 out.print("您還沒有注冊，2秒后轉到注冊界面！"); response.setHeader("refresh","2;url=login.jsp"); %> 如果沒有自動跳轉，請點擊<a href="login.jsp" rel="external nofollow" >此處</a>進行跳轉 <% //response.sendRedirect("login.jsp"); }%> </body></html>
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