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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 javawebUSE javawebCREATE 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")

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。

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"%>
   	
   
    		用户名：
    
    
		密码：
    
    
		
    自动登录
    
		
    
    
	
   

浏览器打开这个login.jsp效果如下

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.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

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"%>
   	欢迎你，${user.username }

部署测试

部署代码，浏览器访问/login.jsp，测试以下登录看看。

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。

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