JDBC工具类实现登录功能

use student;
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');

url=jdbc:mysql://localhost:3306/student
username=root
password=root
driver=com.mysql.jdbc.Driver

package cn.itcast.util;

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

/**
 *   JDBC工具类
 **/
public class JDBCUtils {
    private static String url;
    private static String username;
    private static String password;
    private static String driver;
    /**
     * 文件的读取，著需要读取一次即可拿到这些值，使用静态代码块
     **/
    static {

        try {
            //1、读取资源文件，获取值
            Properties properties = 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 resource = classLoader.getResource("jdbc.properties");
            String path = resource.getPath();

            //2、加载文件
            properties.load(new FileReader(path));
            //3、获取数据，赋值
            url = properties.getProperty("url");
            username = properties.getProperty("username");
            password = properties.getProperty("password");
            driver = properties.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,username,password);
    }

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

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

package cn.itcast.jdbc;

import cn.itcast.util.JDBCUtils;

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

/**
 *  1、通过键盘录入用户名和密码
 *  2、判断用户是否登录成功
 */
public class JDBCLogin {

    public static void main(String[] args) {
        //1、键盘录入，接收用户和密码
        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 JDBCLogin().login(username,password);
        //3、判断
        if (flag) {
            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陆成功


        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            //1、获取链接
            connection = JDBCUtils.getConnection();
            //2、定义sql
            String sql = "select * from user where username = ? and password = ?";
            //3、获取执行sql的对象
            //为了防止sql注入，实现事务安全，效率更高，必须要用PreparedStatement
            preparedStatement = connection.prepareStatement(sql);
            //给?赋值
            preparedStatement.setString(1,username);
            preparedStatement.setString(2,password);
            //4、执行查询，不需要传递sql
            resultSet = preparedStatement.executeQuery();
            //5、判断：如果是下一行，则返回true
            return resultSet.next();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(resultSet,preparedStatement,connection);
        }
        return false;
    }
}