CREATE TABLE user(
id INT PRIMARY KEY AUTO_INCREMENT,
username VARCHAR(32),
PASSWORD VARCHAR(32)
);

INSERT INTO user VALUES(null,‘zhangsan‘,‘123‘)
INSERT INTO user VALUES(null,‘lisi‘,‘234‘)

package cn.itcast.jdbc;

import cn.itcast.util.JDBCUtils;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;

public class JdbcDemo10 {
    public static void main(String[] args) {
        //1.键盘录入，接收用户名和密码
        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login，因为不是静态方法，所以要创建对象
        boolean flag = new JdbcDemo10().login(username, password);

        //3.判断结果，输出同语句
        if (flag){
            System.out.println("登录成功");
        }else {
            System.out.println("登录失败，用户名或密码错误");
        }
    }

    /**
     * 登录方法
     */
    public boolean login(String username, String password) {
        if (username == null || password == null) {//如果有一个为空就不用去连接数据库，做操作
            return false;
        }
        //连接数据库是否判断成功
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            //1.获取数据库连接
            conn = JDBCUtils.getConnection();
            //2.定义SQL-------------------------------------拼接---------------------------------------------------
            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()){//不用这样写rs.next()返回的就是true，false
                return true;
            }else {
                return false;
            }*/
            return rs.next();//如果有下一行返回true

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

        return false;
    }
}