Filter实现自动用户自动登录的原理（代码实例）

(一)Filter实现自动用户自动登录的原理

1.登录界面将表单数据提交给LoginServlet处理，并把获取的数据保存到Cookie对象中去。

2.AutoLoginFilter拦截用户登录请求，并判断请求是否包含用户自动登录的Cookie，如果有获取用户的账号和密码进行判断。如果为true，将用户信息封装到User对象存入Session域中，从而实现自动登录功能。

实例演示

package com.Entity;
public class User {
    //封装用户的属性
    private String username;
    private String password;
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
}

package com.Servlet;
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 com.Entity.User;
public class LoginServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, 
             HttpServletResponse response)
            throws ServletException, IOException {
        //1.获得用户名和密码
        request.setCharacterEncoding("utf-8");
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        //2.验证输入用户名和密码是否正确
        if ("Kaina".equals(username) && "123".equals(password)) {

            //3.将用户状态 user 对象存入 session域
            User user = new User();
            user.setUsername(username);
            user.setPassword(password);
            request.getSession().setAttribute("user", user);
            //4.发送自动登录的cookie
            String autoLogin = request.getParameter("autologin");
            if (autoLogin != null) {
                //5.注意 cookie 中的密码要加密
                Cookie cookie = new Cookie("autologin", username + "-"
                        + password);
                cookie.setMaxAge(Integer.parseInt(autoLogin));
                cookie.setPath(request.getContextPath());
                response.addCookie(cookie);
            }
        //6.跳转至首页
        response.sendRedirect(request.getContextPath()+"/index.jsp");
        } else {
            request.setAttribute("errerMsg", "用户名或密码错");
            request.getRequestDispatcher("/login.jsp")
            .forward(request,response);
        }
    }
    public void doPost(HttpServletRequest request, 
          HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

package com.Servlet;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;
public class LogoutServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;
    public void doGet(HttpServletRequest request, 
             HttpServletResponse response)
            throws ServletException, IOException {
        //1.用户注销
        request.getSession().removeAttribute("user");
        //2.从客户端删除自动登录的cookie
        Cookie cookie = new Cookie("autologin", "msg");
        cookie.setPath(request.getContextPath());
        cookie.setMaxAge(0);
        response.addCookie(cookie);
        response.sendRedirect(request.getContextPath()+"/index.jsp"); 
    }
    public void doPost(HttpServletRequest request,
         HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

package com.Filter;
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 com.Entity.User;
public class AutoLoginFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    public void doFilter(ServletRequest req, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        //1.下次用户请求被拦截后，执行以下代码实现自动登录功能！！！
        //1.获得一个名为 autologin 的cookie
        Cookie[] cookies = request.getCookies();
        String autologin = null;
        for (int i = 0; cookies != null && i < cookies.length; i++) {
            if ("autologin".equals(cookies[i].getName())) {
                //2.找到了指定的cookie
                autologin = cookies[i].getValue();
                break;
            }
        }
        if (autologin != null) {
            //3.做自动登录
            String[] parts = autologin.split("-");
            String username = parts[0];
            String password = parts[1];
            //4.检查用户名和密码
            if ("itcast".equals(username)&& ("123456").equals(password)) {
                // 登录成功,将用户状态 user 对象存入 session域
                User user = new User();
                user.setUsername(username);
                user.setPassword(password);
                request.getSession().setAttribute("user", user);
            }
        }
        // 放行
        chain.doFilter(request, response);
    }
    public void destroy() {
    }
}

package com.Filter;
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 com.Entity.User;
public class AutoLoginFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    public void doFilter(ServletRequest req, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        //1.下次用户请求被拦截后，执行以下代码实现自动登录功能！！！
        //1.获得一个名为 autologin 的cookie
        Cookie[] cookies = request.getCookies();
        String autologin = null;
        for (int i = 0; cookies != null && i < cookies.length; i++) {
            if ("autologin".equals(cookies[i].getName())) {
                //2.找到了指定的cookie
                autologin = cookies[i].getValue();
                break;
            }
        }
        if (autologin != null) {
            //3.做自动登录
            String[] parts = autologin.split("-");
            String username = parts[0];
            String password = parts[1];
            //4.检查用户名和密码
            if ("itcast".equals(username)&& ("123456").equals(password)) {
                // 登录成功,将用户状态 user 对象存入 session域
                User user = new User();
                user.setUsername(username);
                user.setPassword(password);
                request.getSession().setAttribute("user", user);
            }
        }
        // 放行
        chain.doFilter(request, response);
    }
    public void destroy() {
    }
}

<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8" import="java.util.*"
%>
<%@ taglib prefix="c" uri="https://java.sun.com/jsp/jstl/core"%>

  Project01
  
    index.jsp
  
  
    
    LogoutServlet
    LogoutServlet
    com.Servlet.LogoutServlet
  
  
    LogoutServlet
    /LogoutServlet
  
  
    
    LoginServlet
    LoginServlet
    com.Servlet.LoginServlet
  
  
    LoginServlet
    /LoginServlet
  
  
    AutoLoginFilter
    AutoLoginFilter
    com.Filter.AutoLoginFilter
  
  
    AutoLoginFilter
    
    /*
  

输出https://localhost/Project01/login.jsp：

关闭浏览器后，再次打开浏览器输入https://localhost/Project01/index.jsp：