JavaWeb学习-Filter-3-Filter实现自动登录

约定不等于承诺〃 2021-10-23 17:12 350阅读 0赞

本篇来做一个Filter的练习题，就是网站自动登录的，这个自动登录，我们在学习cookies的时候做过，这次使用Filter来做一遍。

**数据库表准备**

首先，我们需要准备一个表，用户表，如果没有可以参考以下SQL去创建。

CREATE DATABASE javaweb
    
    USE javaweb
    
    CREATE TABLE users(
        id INT PRIMARYKEY AUTO_INCREMENT,
        username VARCHAR(100),
        password VARCHAR(100),
        email VARCHAR(150)
    )
    
    INSERT INTO USER VALUES(NULL, "tom", "123","tom@163.com")

![20190815223511343.png][]

**创建一个java web项目**

拷贝相关jar和数据库连接配置文件。以下全部文件都可以从前面图书管理系统中拷贝过来，Dao和Service和servlet代码我们接下来会重写写。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70][]

**写一个用户登录的jsp页面**

写一个登录的jsp页面，有用户名和密码和登录，以及自动登录这个checkbox。

<%@ page language="java" 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=ISO-8859-1">
    <title>Insert title here</title>
    </head>
    <body>
    	<form action="">
    		用户名：<input type="text" name="username" /><br/>
    		密码：<input type="password" name="password" /><br/>
    		<input type="checkbox" name="autoLogin"/>自动登录<br/>
    		<input type="submit" value="登录"/><br/>
    	</form>
    </body>
    </html>

浏览器打开这个login.jsp效果如下

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70 1][]

**Dao层代码**

一个接口和一个实现类文件代码。

package com.anthony.dao;
    
    import java.sql.SQLException;
    
    import com.anthony.domain.User;
    
    public interface UserDao {
    	
    	public User findUser(String username, String password) throws SQLException;
    
    }

具体实现类代码

package com.anthony.dao;
    
    import java.sql.SQLException;
    
    import org.apache.commons.dbutils.QueryRunner;
    import org.apache.commons.dbutils.handlers.BeanHandler;
    
    import com.anthony.datasource.C3P0Utils;
    import com.anthony.domain.User;
    
    public class UserDaoImpl implements UserDao {
    
    	@Override
    	public User findUser(String username, String password) throws SQLException {
    		QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());
    		User user = qr.query("select * from users where username=? and password=?", new BeanHandler<User>(User.class), username, password);
    		return user;
    	}
    
    }

**Service层代码**

一个接口和一个实现类文件代码。

package com.anthony.service;
    
    import com.anthony.domain.User;
    
    public interface UserService {
    	
    	public User findUser(String username, String password);
    
    }

package com.anthony.service;
    
    import java.sql.SQLException;
    
    import com.anthony.dao.UserDao;
    import com.anthony.dao.UserDaoImpl;
    import com.anthony.domain.User;
    
    public class UserServiceImpl implements UserService {
    	
    	// 创建一个Dao层对象
    	UserDao ud = new UserDaoImpl();
    
    	@Override
    	public User findUser(String username, String password) {
    		try {
    			return ud.findUser(username, password);
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    		return null;
    	}
    }

**Servlet代码**

新建一个LoginServlet.java的servlet，url映射为/loginServlet

package com.anthony.web.servlet;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    import com.anthony.domain.User;
    import com.anthony.service.UserService;
    import com.anthony.service.UserServiceImpl;
    
    public class LoginServlet extends HttpServlet {
    	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		String username = request.getParameter("username");
    		String password = request.getParameter("password");
    		
    		UserService us = new UserServiceImpl();
    		User user = us.findUser(username, password);
    		
    		if(user != null) {
    			request.getSession().setAttribute("user", user);
    			request.getRequestDispatcher("/home.jsp").forward(request, response);
    		}else {
    			request.setAttribute("msg", "用户名或密码错误，请重新登录。");
    			request.getRequestDispatcher("/login.jsp").forward(request, response);
    		}
    	}
    	
    	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    
    }

**创建home.jsp**

这个页面用来显示 欢迎你，用户名

**部署测试**

部署代码，浏览器访问/login.jsp，测试以下登录看看。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70 2][]

**添加Filter**

前面已经实现了登录功能，下面开始使用Filter相关代码来实现自动登录。到这里，Filter主要做这几件事

*  从cookies中取出用户账户相关信息
 *  执行登录操作
 *  放行，直接跳转到/home.jsp页面。

先把LoginServlet中代码添加cookie相关代码。

package com.anthony.web.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.anthony.domain.User;
    import com.anthony.service.UserService;
    import com.anthony.service.UserServiceImpl;
    
    public class LoginServlet extends HttpServlet {
    	
    	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		String username = request.getParameter("username");
    		String password = request.getParameter("password");
    		
    		UserService us = new UserServiceImpl();
    		User user = us.findUser(username, password);
    		if(user != null) {
    			String autoLogin = request.getParameter("autoLogin");
    			// 拿到这个cookie，可以通过&切割拿到用户名和密码
    			Cookie cookie = new Cookie("user", user.getUsername()+"&"+user.getPassword());
    			cookie.setPath("/");
    			if(autoLogin != null) {
    				cookie.setMaxAge(60*60*24*7); // 设置有效期为7天
    			}else {
    				cookie.setMaxAge(0);
    			}
    			response.addCookie(cookie); //把cookie保存到客户端
    			request.getSession().setAttribute("user", user);
    			request.getRequestDispatcher("/home.jsp").forward(request, response);
    			
    		}else {
    			request.setAttribute("msg", "用户名或密码错误，请重新登录。");
    			request.getRequestDispatcher("/login.jsp").forward(request, response);
    		}
    	}
    	
    	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    
    }

创建一个Filter，代码如下。

package com.anthony.web.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 javax.servlet.http.HttpServletResponse;
    
    import com.anthony.domain.User;
    import com.anthony.service.UserService;
    import com.anthony.service.UserServiceImpl;
    
    
    public class AutoLoginFilter implements Filter {
    
        
    	public void destroy() {
    
    	}
    
    	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    		
    		// 1 转换两个对象 HttpServletRequest HttpServletResponse
    		HttpServletRequest req = (HttpServletRequest) request;
    		HttpServletResponse resp = (HttpServletResponse) response;
    		
    		// 2.处理业务, 这里是得到cookies
    		Cookie[] cookies = req.getCookies();
    		String username = "";
    		String password = "";
    		for (int i = 0; cookies != null && i < cookies.length; i++) {
    			if("user".equals(cookies[i].getName())) {
    				String value = cookies[i].getValue(); // username&password这样一个格式字符串
    				// 得到用户名和密码
    				String[] values = value.split("&");
    				username = values[0];
    				password = values[1];
    			}
    		}
    		UserService us = new UserServiceImpl();
    		User u = us.findUser(username, password);
    		
    		if(u != null) { // 如果登录成功，把用户信息存到session中
    			req.getSession().setAttribute("user", u);
    		}
    		// 3.放行
    		chain.doFilter(request, response);
    	}
    
    	public void init(FilterConfig fConfig) throws ServletException {
    	
    	}
    
    }

**部署测试**

部署tomcat之后，打开浏览器先访问/login.jsp，出现登录界面，输入tom/123，记得勾选自动登录，然后可以看到欢迎用户的打印内容。关闭浏览器，再次打开浏览器，访问/home.jsp, 如果直接显示欢迎xxx用户，说明实现自动登录。

[20190815223511343.png]: /images/20211023/8677134015fe4f0b8dda647c71482bf8.png
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70 1]: /images/20211023/39ba8e6d9b8344e6901b1ed9444d5c15.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70 2]: /images/20211023/ad6daa9189c44db4b287d0c3981de66b.png