千山万水，一帘烟雨，迷离了眼眸。
理解并掌握Cookie的作用以及利用cookie实现用户的自动登录功能，实现下图效果
当服务器判断出该用户是首次登录的时候，会自动跳转到登录界面等待用户登录，并填入相关信息。通过设置Cookie的有效期限来保存用户的信息，关闭浏览器后，验证是否能够自动登录，若能登录，则打印欢迎信息；否则跳转到登录页面。
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 rel="nofollow noopener noreferrer" 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" rel="nofollow noopener noreferrer" href="styles.css" rel="external nofollow" rel="external nofollow" >
-->
<script type="text/javascript">
window.onload = function(){
//获取submit
var submit = document.getElementById("submit");
var name = document.getElementById("name");
//为submit绑定单击响应函数
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("只能选择一个选项");
return false;
}
};
};
</script>
</head>
<body>
<!-- 设置html页面 -->
<form action="sucess.jsp" method="post">
用户名：<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="登录"/>
</form>
<%
//读取session值
String val= (String)session.getAttribute("name");
//如果session不存在
if(val==null){
val ="不存在";
}
out.print("当前\""+val+"\"用户可自动登录");
%>
</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 rel="nofollow noopener noreferrer" 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" rel="nofollow noopener noreferrer" href="styles.css" rel="external nofollow" rel="external nofollow" >
-->
</head>
<body>
<%
//获取username
String name = request.getParameter("username");
//判断用户名是否存在
if(name != null && !name.trim().equals("")){
String[] time = request.getParameterValues("time");
//设置session值，便于login页面读取
session.setAttribute("name", name);
//设置Cookie
Cookie Cookie = new Cookie("name",name);
//根据提交选项设置cookie保存时间
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，设置为100年
if(time[i].equals("forever")){
Cookie.setMaxAge(60*60*24*365*100);
}
}
}
//在客户端保存Cookie
response.addCookie(Cookie);
}
else{%>
<%--用户名不存在则进行判断是否已有cookie --%>
<%
//获取cookie
Cookie[] cookies = request.getCookies();
//cookie存在
if(cookies != null && cookies.length > 0){
for(Cookie cookie:cookies){
//获取cookie的名字
String cookieName = cookie.getName();
//判断是否与name相等
if(cookieName.equals("name")){
//获取cookie的值
String value = cookie.getValue();
name = value;
}
}
}
}
if(name != null && !name.trim().equals("")){
out.print("您好: " + name+"欢迎登录");
}
else{//否则重定向到登录界面
out.print("您还没有注册，2秒后转到注册界面！");
response.setHeader("refresh","2;url=login.jsp");
%>
如果没有自动跳转，请点击<a rel="nofollow noopener noreferrer" href="login.jsp" rel="external nofollow" >此处</a>进行跳转
<%
//response.sendRedirect("login.jsp");
}
%>
</body>
</html>
实现效果：
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本文javascriptp如何实现用户自动登录功能到此结束。擦干当年所有的泪，所有的痛，遗忘悲伤，重新来过。小编再次感谢大家对我们的支持！
