题目：编写一个用户登录页面（如果是ip地址为“192”开头的客户访问，则在页面显示该用户的ip地址），输入账号和密码，让用户选择“是否保存登录状态”，如果账号密码相等，则登
题目：编写一个用户登录页面（如果是ip地址为“192”开头的客户访问，则在页面显示该用户的ip地址），输入账号和密码，让用户选择“是否保存登录状态”，如果账号密码相等，则登陆成功，进入欢迎页面。
在登录时，如果保存了登录状态，下次登录时，如果访问登录页面，则进入欢迎页面。但是，客户如果没有经过登录就访问欢迎页面，则跳转到登录页面。
以下为思路分析，其中，前端用Bootstrap框架实现，后台基于JSP+Servlet+Mysql实现。代码下载(网盘，永久有效)：http://pan.baidu.com/s/1bo9qwIb，后台数据库需自己创建和修改。
思路分析：
1.当访客访问登陆页面welcome.jsp，先判断是否存在保存的cookie，如果是则跳转到欢迎页面bootstrap.jsp，如果不存在cookie则输入登陆信息；以下为登陆页面代码：welcome.jsp
<%@page language="java" pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<!-- 引入 Bootstrap -->
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
<title>欢迎登录</title>
</head>
<body>
<% //首先进入登陆页面先判断是否存在cookie，如果是跳转到欢迎界面 Cookie[] cookies=request.getCookies(); if(cookies!=null){ for(int i=0;i<cookies.length;i++) { if(cookies[i].getName().equals("name")){ //如果cookie与保存的相等，即找到cookie response.sendRedirect("bootstrap.jsp"); } } } %>
<br><br><br><br><br>
<div class="jumbotron">
<div class="container">
<form action="servlet/servlet_login" method="post" class="form-horizontal" role="form"><br><br>
<div class="form-group">
<label class="col-sm-2 col-md-offset-4 control-label" ><span class="glyphicon glyphicon-user"></span>数据库账户：</label>
<div class="col-sm-6">
<input type="text" class="form-control" style="width:30%" name="name" value="" placeholder="请输入账户名"><br><br>
</div>
</div>
<div class="form-group">
<label class="col-sm-2 col-md-offset-4 control-label"><span class="glyphicon glyphicon-ok-circle"></span>数据库密码：</label>
<div class="col-sm-6">
<input type="text" class="form-control" style="width:30%" name="password" value="" placeholder="请输入密码"><br><br>
</div>
<!--打勾-->
<div class="checkbox col-sm-2 col-md-offset-6">
<label>
<input type="checkbox" name="save">保存密码
</label>
</div>
</div>
<input type="submit" class="col-sm-1 col-md-offset-5 btn btn-primary" value="登陆">
<input type="reset" class="col-sm-1 col-md-offset-1 btn btn-primary" value="重置">
</form>
<%!public String getIpAddr(HttpServletRequest request) { String ip = request.getHeader("x-forwarded-for"); if(ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) { ip = request.getHeader("Proxy-Client-IP"); } if(ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) { ip = request.getHeader("WL-Proxy-Client-IP"); } if(ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) { ip = request.getRemoteAddr(); } if(ip.startsWith("192")){} else{ip="";} return ip; }%>
<label class="col-sm-4 col-md-offset-5 control-label">
<span class="glyphicon glyphicon-ok-circle" style="color: rgb(255, 0, 28); font-size: 14px;">你的IP地址为：</span>
<%=getIpAddr(request)%></label>;
</div>
</div>
</body>
</html>
2.当用户输入登陆用户名及密码时，提交到后台的servlet_login，servlet此时从web.xml中读取数据库用户名及密码进入数据库，从中查询用户名及密码是否正确，如果正确则判断用户是否勾选了保存密码；
3.如果用户勾选了保存密码，则设置cookie存活时间为1天(60*60*24)，如果没有勾选保存密码的话就设置cookie存活时间为19s(为了便于验证，当然也可以设置更久);以下为servlet_login代码：servlet_login.java
package servlet;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/** * Servlet implementation class servlet_login */
@WebServlet("/servlet_login")
public class servlet_login extends HttpServlet {
private static final long serialVersionUID = 1L;
Connection conn = null;
Statement stmt = null;
public void init(ServletConfig config) throws ServletException {
//载入连接数据库的信息
//ServletContext application=this.getServletContext();
String driverClass =config.getInitParameter("driverClass");
String url=config.getInitParameter("url");
String username = config.getInitParameter("username");
String password = config.getInitParameter("password");
System.out.println(username+"\n"+password);
//连接数据库MySQL，进行验证
try {
Class.forName(driverClass);
conn = DriverManager.getConnection(url,username,password);//得到连接
System.out.println("数据库连接成功");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}//加载驱动
catch (SQLException e) {
e.printStackTrace();
}
}
/** * @see HttpServlet#HttpServlet() */
public servlet_login() {
super();
// TODO Auto-generated constructor stub
}
/** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doPost(request, response);
//response.getWriter().append("Served at: ").append(request.getContextPath());
}
/** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
//先判断cookie是否存在
Cookie[] cookies=request.getCookies();
if(cookies!=null){
for(int i=0;i<cookies.length;i++) {
if(cookies[i].getName().equals("name")){
//如果cookie与保存的相等，即找到cookie
response.sendRedirect("/Test666/bootstrap.jsp");break;
}
}
}
System.out.println("即将进行数据库查询");
//比较账号及密码是否正确
try {
stmt = conn.createStatement();
String name=request.getParameter("name");
String password=request.getParameter("password");
System.out.println(name+" "+password+"\n");
String sql="select * from count where name='"+name+"' and password='"+password+"'";
ResultSet rs=stmt.executeQuery(sql);
if(rs.next()==true) {//存在这个账户，密码
System.out.println("账户，密码正确");
//如果用户勾选了保存密码，则保留用户登陆信息,将用户名name存入Cookie
//此处判断是否勾选保存密码
//response.getWriter().append(request.getParameter("save"));
if(request.getParameter("save")!=null) {//如果勾选了保存密码
response.getWriter().append(request.getParameter("save"));
Cookie cookie=new Cookie("name",request.getParameter("name"));
cookie.setPath("/");//保证cookie存放的根目录相同
//设置cookie存活时间为1天
cookie.setMaxAge(60*60*24);
//将cookie保存在客户端
response.addCookie(cookie);
}
else {//如果没有勾选保存密码
Cookie cookie=new Cookie("name",request.getParameter("name"));
cookie.setPath("/");//保证cookie存放的根目录相同
//设置cookie存活时间为19s
cookie.setMaxAge(19);
//将cookie保存在客户端
response.addCookie(cookie);
}
//response.getWriter().append("欢迎登陆");
response.sendRedirect("/Test666/bootstrap.jsp");
System.out.println("测试，已跳转");
return ;
}
else {
System.out.println("账户及密码错误");
//如果账户，密码错误，则返回登陆界面
response.sendRedirect("/Test666/welcome.jsp");return ;
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}//Ending
}
}
4.添加cookie后，重定向到bootstrap.jsp欢迎页面，在欢迎页面先判断cookie是否存在，如果符合则显示欢迎页面内容，如果不符合则跳转到登陆页面。以下为欢迎页面代码：bootstrap.jsp
<%@ page language="java" pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<!-- 引入 Bootstrap -->
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
<title>Insert title here</title>
</head>
<body>
<% Cookie[] cookies=request.getCookies(); boolean flag=false; if(cookies!=null){ System.out.println("cookie的长度为："+cookies.length); for(int i=0;i<cookies.length;i++) { if(cookies[i].getName().equals("name")){ //如果cookie与保存的相等，即找到cookie flag=true;break; //response.sendRedirect("bootstrap.jsp"); } } } if(flag==false){response.sendRedirect("welcome.jsp");}//如果没找到cookie，就返回登陆界面 %>
<div class="container">
<div class="row clearfix">
<div class="col-md-12 column">
<nav class="navbar navbar-default" role="navigation">
<div class="navbar-header">
<button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1"> <span class="sr-only">Toggle navigation</span><span class="icon-bar"></span><span class="icon-bar"></span><span class="icon-bar"></span></button> <a class="navbar-brand" href="#">导航1</a>
</div>
<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
<ul class="nav navbar-nav">
<li class="active">
<a href="#">导航2</a>
</li>
<li>
<a href="#">导航3</a>
</li>
<li class="dropdown">
<a href="#" class="dropdown-toggle" data-toggle="dropdown">导航4<strong class="caret"></strong></a>
<ul class="dropdown-menu">
<li>
<a href="#">Action</a>
</li>
<li>
<a href="#">Another action</a>
</li>
<li>
<a href="#">Something else here</a>
</li>
<li class="divider">
</li>
<li>
<a href="#">Separated link</a>
</li>
<li class="divider">
</li>
<li>
<a href="#">One more separated link</a>
</li>
</ul>
</li>
</ul>
<form class="navbar-form navbar-left" role="search">
<div class="form-group">
<input type="text" class="form-control" />
</div> <button type="submit" class="btn btn-default">Submit</button>
</form>
<ul class="nav navbar-nav navbar-right">
<li>
<a href="#"></a>
</li>
<li class="dropdown">
<a href="#" class="dropdown-toggle" data-toggle="dropdown">Dropdown<strong class="caret"></strong></a>
<ul class="dropdown-menu">
<li>
<a href="#">Action</a>
</li>
<li>
<a href="#">Another action</a>
</li>
<li>
<a href="#">Something else here</a>
</li>
<li class="divider">
</li>
<li>
<a href="#">Separated link</a>
</li>
</ul>
</li>
</ul>
</div>
</nav>
<div class="jumbotron">
<h1>
欢迎登录！
</h1>
<p>
欢迎来到登录界面！
</p>
<p>
<a class="btn btn-primary btn-large" href="#">Learn more</a>
</p>
</div>
</div>
</div>
</div>
</body>
</html>
5.当然，如果访客没经过登陆，直接访问欢迎页面bootstrap.jsp也会由于判断cookie不存在而跳转到登陆页面，最后，web.xml设置如下：
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>Test666</display-name>
<servlet>
<servlet-name>servlet_login</servlet-name>
<servlet-class>servlet.servlet_login</servlet-class>
<init-param>
<param-name>driverClass</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</init-param>
<init-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/count?useUnicode=true&characterEncoding=utf-8</param-value>
</init-param>
<init-param>
<param-name>username</param-name>
<param-value>root</param-value>
</init-param>
<init-param>
<param-name>password</param-name>
<param-value>160337</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>servlet_login</servlet-name>
<url-pattern>/servlet/servlet_login</url-pattern>
</servlet-mapping>
<filter>
<filter-name>EncodingFilter</filter-name>
<filter-class>Filter.EncodingFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>EncodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<welcome-file-list>
<welcome-file>welcome.jsp</welcome-file>
</welcome-file-list>
</web-app>