JDBC用户登录demo

 mysql列表：

JAVA代码：

第一段用statement方法，有sql注入危险，实际工程一般不会使用

package cn.itcast.jdbc;

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

public class jdbcDemo3 {
//    创建user表
//    create table USER(
//        id INT PRIMARY KEY AUTO_INCREMENT,
//        username VARCHAR(32),
//    password VARCHAR(32)
//    );
    
    public static void main(String[] args) {
        //1.输入用户名和密码
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入用户名：");
        System.out.println("请输入密码：");
        String username = sc.nextLine();
        String password = sc.nextLine();
        //2.调用login方法
        boolean flag = new jdbcDemo3().login(username, password);
        //3.判断结果 输出语句
        if(flag) System.out.println("登录成功");
        else System.out.println("登录失败");
    }

    
    public boolean login(String username,String password){
        //连接数据库
        //*****
        Statement stmt = null;
        Connection conn = null;
        ResultSet rs = null;
        //1.导入jar包
        //2.注册驱动
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            //3.获取数据库连接对象
            conn  = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/user_id?serverTimezone=GMT%2b8","root","sujie123");
            //4.定义sql语句
            String sql = "select * from USER where username = '"+username+"'and password = '"+password+"'";
            //5.获取执行的对象statement
            stmt  = conn.createStatement();
            //6.执行sql语句
            //int count = //更新语句
            rs = stmt.executeQuery(sql);
            //7.处理结果
            return rs.next();
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }finally {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    return false;
    }
}

第二段代码用PrepareStatement方法，安全性更高，主要在于获取用户名和密码验证方式不同

package cn.itcast.jdbc;

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

public class jdbcDemo3 {
//    创建user表
//    create table USER(
//        id INT PRIMARY KEY AUTO_INCREMENT,
//        username VARCHAR(32),
//    password VARCHAR(32)
//    );

    public static void main(String[] args) {
        //1.输入用户名和密码
        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login方法
        boolean flag = new jdbcDemo3().login(username, password);
        //3.判断结果 输出语句
        if(flag) System.out.println("登录成功");
        else System.out.println("登录失败");
    }


    public boolean login(String username,String password){
        //连接数据库
        //*****
        PreparedStatement pstmt = null;
        Connection conn = null;
        ResultSet rs = null;
        //1.导入jar包
        //2.注册驱动
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            //3.获取数据库连接对象
            conn  = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/user_id?serverTimezone=GMT%2b8","root","sujie123");
            //4.定义sql语句
            String sql = "select * from USER where username =? and password =?";
            //5.获取执行的对象statement
            pstmt  = conn.prepareStatement(sql);
            //赋值操作
            pstmt.setString(1,username);
            pstmt.setString(2,password);
            //6.执行sql语句
            //int count = //更新语句
            rs = pstmt.executeQuery();
            //7.处理结果
            return rs.next();
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }finally {
            try {
                pstmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    return false;
    }
}

输出结果：