（4）User.java 文件：
package com.pojo; //用来存放用户登录时，输入输出的信息 public class User { private String uname; private String upwd; private String role; public String getUname() { return uname; } public void setUname(String uname) { this.uname = uname; } public String getUpwd() { return upwd; } public void setUpwd(String upwd) { this.upwd = upwd; } public String getRole() { return role; } public void setRole(String role) { this.role = role; } }（5）UserDAO.java 文件：
package com.dao; import com.dbutil.DBUtils; import com.pojo.User; public class UserDAO { //返回 0 或 1 public int login(User user){ DBUtils dbUtils = new DBUtils(); //与数据库是否匹配，匹配为 1 int temp = dbUtils.login(user); return temp; } }（6）DBUtils.java 文件：
！！！ 成败在与这个文件
自行更改数据库名
自行更改表名（两个）
自行更改 root 的密码
检查服务是否启动
package com.dbutil; import com.pojo.User; import java.sql.*; public class DBUtils { Connection conn; //预处理 PreparedStatement pstmt; //结果集 ResultSet rs; public DBUtils(){ try{ Class.forName("com.mysql.cj.jdbc.Driver"); conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/数据库名?useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC","root","密码"); } catch (Exception e){ e.printStackTrace(); } } public int login(User user){ try{ pstmt=conn.prepareStatement("select * from 表名 where uname = ? and upwd = md5(?)"); pstmt.setString(1, user.getUname()); pstmt.setString(2, user.getUpwd()); rs = pstmt.executeQuery(); if (rs.next()) return 1; else return 0; }catch (Exception e){ e.printStackTrace(); } return 0; } }（7）Servlet.java 文件：
package com.loginServlet; import com.pojo.User; import com.service.UserService; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; @WebServlet(name = "Servlet",urlPatterns = "/Servlet") public class Servlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("doPost"); request.setCharacterEncoding("utf-8"); //获取 post 请求中的两个参数 String uname = request.getParameter("uname"); String upwd = request.getParameter("upwd"); String role = request.getParameter("role"); /*硬编码, 不从数据库获取信息，直接验证 if (uname.equals("admin") && upwd.equals("123456")) { response.sendRedirect("index.jsp"); }else{ response.sendRedirect("loginServlet.html"); }*/ //从服务获取值 UserService userService = new UserService(); User user = new User(); user.setUname(uname); user.setUpwd(upwd); user.setRole(role); if (userService.login(user)) { response.sendRedirect("index.jsp"); }else{ response.sendRedirect("failed.jsp"); } } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("doGet"); } }（8）UserService.java 文件：
package com.service; //服务层，给控制层提供服务 import com.dao.UserDAO; import com.pojo.User; public class UserService { UserDAO dao = new UserDAO(); //参数，处理 User 对象，返回 True 或 False public boolean login(User user){ int temp = dao.login(user); if (temp == 0) return false; else return true; } } 四、运行调试
（1）MySQL 8.0 版本的 jdbc 个数据版本不匹配
（2）数据库服务没有运行
（3）配置文件数据库信息没有自行更改
（4）文件名自定义时，依赖失败
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