db.properties

driverClassName = com.mysql.cj.jdbc.Driver
username = root
password = 123456
url = jdbc:mysql://localhost:3306/test?serverTimezone=UTC

JDBCUtils

package utils;


import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Properties;

public class JDBCUtils {

    private static Properties properties = new Properties();

    static {
        try {
            InputStream inputStream = Thread.currentThread().getContextClassLoader().getResourceAsStream("db.properties");
            properties.load(inputStream);

            Class.forName(properties.getProperty("driverClassName"));
        } catch (Exception e){
            e.printStackTrace();
        }
    }

    public static Connection getConn(){
        try {
           return DriverManager.getConnection(
                   properties.getProperty("url"),
                   properties.getProperty("username"),
                   properties.getProperty("password"));
        } catch (Exception e){
            e.printStackTrace();
        }
        return null;
    }

    public static void close(Connection conn, Statement st, ResultSet rs){
        try{
            if (rs != null){
                rs.close();
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try {
                if (st != null){
                    st.close();
                }
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                try {
                    if (conn != null){
                        conn.close();
                    }
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        }
    }
}

domian

package domain;

import lombok.Data;

@Data
public class User {
    private int id;
    private String username;
    private String password;
}

LoginServlet

package server;

import dao.UserDao;
import domain.User;

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("/loginServlet")
public class LoginServlet extends HttpServlet {

    /**
     * 编写业务逻辑代码
     * @param req
     * @param resp
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //1.设置编码格式
        req.setCharacterEncoding("utf-8");

        //2.获取请求参数
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        //3.封装User对象
        User loginUser = new User();
        loginUser.setUsername(username);
        loginUser.setPassword(password);

        //4.调用UserDao类中登录方法
        UserDao userDao = new UserDao();


        User user = userDao.login(loginUser);

        //5.进行判断
        if (user == null){
            req.getRequestDispatcher("/failServlet").forward(req,resp);
        }

        //存储数据
        req.setAttribute("user",user);

        //转发
        req.getRequestDispatcher("successServlet").forward(req,resp);

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req,resp);
    }
}

SuccessServlet

package server;

import domain.User;

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("/successServlet")
public class SuccessServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       User user = (User) req.getAttribute("user");

        if(user != null){
            //给页面写一句话

            //设置编码
            resp.setContentType("text/html;charset=utf-8");
            //输出
            resp.getWriter().write("登录成功！"+user.getUsername()+",欢迎您");
        }

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req,resp);
    }
}

FailServlet

package server;

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("/failServlet")
public class FailServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //给页面写一句话

        //设置编码
        resp.setContentType("text/html;charset=utf-8");
        //输出
        resp.getWriter().write("登录失败，用户名或密码错误");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req,resp);
    }
}