基础知识理解：
cookie、session和过滤器通常都是用在web应用中，cookie和session用来保存一定的数据，过滤器Filter则是在浏览器发出请求之后，而后台执行特定的请求之前发生一定的作用。之所以把这三个放一起，是因为有很多时候都会是把他们结合在一起使用，例如有些登陆程序。
cookie是浏览器的机制，session是服务器的机制，但是实际上cookie也是由服务器生成的，之后返回给浏览器的，并不是浏览器本身生成。当浏览器发送某个请求时，如果拥有有效的cookie则会把这个cookie带在一起。
之所有会有cookie的使用，是因为http协议原本是无状态协议，也就是说通过http协议本身，服务器不能判断浏览器是否之前访问过。
Filter和servlet的写法相似，编写相关代码的时候需要实现Filter接口并重写相关的方法，通常更改较多的是doFilter方法。Filter代码写好以后如果需要发生效用，需要像配置servlet一样在web.xml中 进行一定的配置。
以下是一个简单的结合cookie、session、Servlet和Filter的登陆示例代码：
定义一个用户实体类，充当数据库数据，这里使用单例模式，保证只存在一个实例对象：
package models;
/**
*用户信息实体类
*@author tuzongxun123
*/
public class UserModel {
private String userName;
private String password;
// 单例模式，保证只有一个用户对象实例
public static UserModel getInstance() {
UserModel user = new UserModel("zhangsan", "123456");
return user;
}
private UserModel(String userName, String pasword) {
this.userName = userName;
this.password = pasword;
}
public String getUserName() {
return userName;
}
public String getPassword() {
return password;
}
}
用户登陆输入信息index.jsp界面，在form表单的action中使用jsp的特性获得项目路径：
<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>cookieAndFilterTest
</head>
<body>
<form action="<%=request.getContextPath() %>/loginServlet" method="post">
userName：<input type="text" name="userName" /></br>
password：<input type="password" name="password" /></br>
<input type="submit" value="login"/>
</form>
</body>
</html>
对应的后台servlet：
package servletTest;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import models.UserModel;
public class LoginServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
this.doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
String userName = req.getParameter("userName");
String password = req.getParameter("password");
// 模拟数据库数据
UserModel user = UserModel.getInstance();
String dbUserName = user.getUserName();
String dbPassword = user.getPassword();
if (dbUserName.equals(userName) && dbPassword.equals(password)) {
// 用户名和密码都匹配，证明登陆成功，设置session和cookie
HttpSession session = req.getSession();
session.setAttribute("userName", userName);
session.setAttribute("password", password);
Cookie cookie = new Cookie("userName", userName);
Cookie cookie2 = new Cookie("password", password);
// 设置cookie的存储时长
cookie.setMaxAge(60);
cookie2.setMaxAge(60);
// 把cookie发送给浏览器
resp.addCookie(cookie);
resp.addCookie(cookie2);
// 转发请求到用户列表
req.getRequestDispatcher("/userList").forward(req, resp);
} else {
// 转发请求到登陆页面
req.getRequestDispatcher("index.jsp").forward(req, resp);
}
}
}
上边登陆后跳转的请求：
package servletTest;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import models.UserModel;
public class UserListServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
this.doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
UserModel user = UserModel.getInstance();
//在浏览器中打印出用户列表书数据
resp.getWriter().write(
"userName:" + user.getUserName() + "," + "password:"
+ user.getPassword());
}
}
项目web.xml配置：
<?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" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
id="WebApp_ID" version="2.5">
<!-- 访问时的项目名称 -->
<display-name>cookieAndFilterTest</display-name>
<!-- servlet配置 -->
<servlet>
<servlet-name>login</servlet-name>
<servlet-class>servletTest.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>login</servlet-name>
<url-pattern>/loginServlet</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>userList</servlet-name>
<servlet-class>servletTest.UserListServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>userList</servlet-name>
<url-pattern>/userList</url-pattern>
</servlet-mapping>
<!-- 过滤器设置，浏览其发送请求后首先会走这里 -->
<filter>
<filter-name>loginFilter</filter-name>
<filter-class>filterTest.FilterTest</filter-class>
</filter>
<filter-mapping>
<filter-name>loginFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<!-- 输入项目名访问的默认页面 -->
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
java过滤器代码：
package filterTest;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import models.UserModel;
public class FilterTest implements Filter {
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
// 登陆请求、初始请求直接放行
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse resp = (HttpServletResponse) response;
String uri = req.getRequestURI();
if ("/cookieAndFilterTest/loginServlet".equals(uri)
|| "/cookieAndFilterTest/".equals(uri)) {
// 放行
chain.doFilter(request, response);
return;
}
// 不是登陆请求的话，判断是否有cookie
Cookie[] cookies = req.getCookies();
if (cookies != null && cookies.length > 0) {
String userName = null;
String password = null;
// 判断cookie中的用户名和密码是否和数据库中的一致，如果一致则放行，否则转发请求到登陆页面
for (Cookie cookie : cookies) {
if ("userName".equals(cookie.getName())) {
userName = cookie.getValue();
}
if ("password".equals(cookie.getName())) {
password = cookie.getValue();
}
}
UserModel user = UserModel.getInstance();
if (user.getUserName().equals(userName)
&& user.getPassword().equals(password)) {
chain.doFilter(request, response);
return;
} else {
// 重定向到登陆界面
req.getRequestDispatcher("/index.jsp").forward(req, resp);
return;
}
} else {
req.getRequestDispatcher("/index.jsp").forward(req, resp);
return;
}
}
@Override
public void init(FilterConfig arg0) throws ServletException {
}
}
