目录结构：

1、创建一个数据表，命名为user

2、配置类jdbc_properties

url=jdbc:mysql:///student
user=root
password=******
driver=com.mysql.cj.jdbc.Driver

3、JDBCUtils类

package util;
import java.io.FileReader;
import java.io.IOException;
import java.net.URL;
import java.sql.*;
import java.util.Properties;

public class JDBCUtils {
    private static String url;
    private static String user;
    private static String password;
    private static String driver;
    /**
     * 文件的读取，只需要读取一次即可拿到这些值。使用静态代码块
     */
    static{
        //读取资源文件，获取值。

        try {
            //1. 创建Properties集合类。
            Properties pro = new Properties();

            //获取src路径下的文件的方式--->ClassLoader 类加载器
            ClassLoader classLoader = JDBCUtils.class.getClassLoader();
            URL res  = classLoader.getResource("jdbc.properties");
            String path = res.getPath();
            //System.out.println(path);///D:/intellij-idea-project-file/Program1/out/production/Program1/jdbc.properties
            //2. 加载文件
            // pro.load(new FileReader("D:/intellij-idea-project-file/Program1/out/production/Program1/jdbc.properties"));
            pro.load(new FileReader(path));

            //3. 获取数据，赋值
            url = pro.getProperty("url");
            user = pro.getProperty("user");
            password = pro.getProperty("password");
            driver = pro.getProperty("driver");
            //4. 注册驱动
            Class.forName(driver);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }


    /**
     * 获取连接
     * @return 连接对象
     */
    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url, user, password);
    }

    /**
     * 释放资源
     * @param stmt
     * @param conn
     */
    public static void close(Statement stmt,Connection conn){
        if( stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if( conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }


    /**
     * 释放资源
     * @param stmt
     * @param conn
     */
    public static void close(ResultSet rs,Statement stmt, Connection conn){
        if( rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if( stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if( conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

}

4、JDBCDemo1类

package com.mytest1;
import util.JDBCUtils;

import java.sql.*;
import java.util.Scanner;

public class JDBCDemo1 {
    public static void main(String[] args) {
            //1.键盘录入，接受用户名和密码
            Scanner sc = new Scanner(System.in);
            System.out.println("请输入用户名：");
            String username = sc.nextLine();
            System.out.println("请输入密码：");
            String password = sc.nextLine();
            //2.调用方法
            boolean flag = new JDBCDemo1().login(username, password);
            //3.判断结果，输出不同语句
            if(flag){
                //登录成功
                System.out.println("登录成功！");
            }else{
                System.out.println("用户名或密码错误！");
            }
        }

         // 登录方法
        public boolean login(String username ,String password){
            if(username == null || password == null){
                return false;
            }
            //连接数据库判断是否登录成功
            Connection conn = null;
            Statement stmt =  null;
            ResultSet rs = null;
            //1.获取连接
            try {
                conn =  JDBCUtils.getConnection();
                //2.定义sql
                String sql = "select * from user where username = '"+username+"' and password = '"+password+"' ";
                //3.获取执行sql的对象
                stmt = conn.createStatement();
                //4.执行查询
                rs = stmt.executeQuery(sql);
                //5.判断
			           /* if(rs.next()){//如果有下一行，则返回true
			                return true;
			            }else{
			                return false;
			            }*/
                return rs.next();//如果有下一行，则返回true

            } catch (SQLException e) {
                e.printStackTrace();
            }finally {
                JDBCUtils.close(rs,stmt,conn);
            }

            return false;

    }
}

5、运行结果：