JDBC编程，第三种写法，模拟登陆系统（解决SQL注入）

JDBC编程，第三种写法，模拟登陆系统（解决第二种写法中SQL注入的问题）
1、还是一样，利用PowerDesigner建表；

drop table if exists t_user;

/*==============================================================*/
/* Table: t_user                                                */
/*==============================================================*/
create table t_user
(
   id                   bigint auto_increment,
   loginName            varchar(255),
   loginPwd             varchar(255),
   realName             varchar(255),
   primary key (id)
);
insert into t_user(loginName,loginPwd,realName) values('***','***','***');
insert into t_user(loginName,loginPwd,realName) values('***','***','***');
commit;
select * from t_user;

2、完整代码：

import com.mysql.jdbc.Driver;

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

public class Test{
    public static void main(String[] args) {
        //初始化界面
        Map<String,String> userLoginInfo = initUI();
        //验证用户名和密码
        boolean loginSuccess = login(userLoginInfo);
        //输出结果
        System.out.println(loginSuccess ? "登录成功" : "登录失败");
    }
    /**
     * 用户登录
     * @param userLoginInfo 用户登录信息
     * @return false表示失败，true表示成功
     */
    private static boolean login(Map<String, String> userLoginInfo) {
        boolean loginSuccess = false;
        //JDBC准备
        Connection connection = null;
        //预编译的数据库操作对象PreparedStatement
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            //1、注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            // 2、获取连接
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/数据库","root","****");
            // 3、获取预编译的数据库操作对象
            //sql框架
            String sql= "select * from t_user where loginName = ? and loginPwd = ?";
            //把带有占位符的sql语句传入操作对象
            preparedStatement = connection.prepareStatement(sql);
            //给占位符传值，下标从1开始
            preparedStatement.setString(1,userLoginInfo.get("userName"));
            preparedStatement.setString(2,userLoginInfo.get("userPwd"));
            //4、执行sql
            resultSet= preparedStatement.executeQuery();
            //5、处理结果集
            if (resultSet.next()){
                loginSuccess = true;
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //6、释放资源
            if (resultSet != null) {
                try {
                    resultSet.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (preparedStatement != null) {
                try {
                    preparedStatement.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (connection != null) {
                try {
                    connection.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
        return loginSuccess;
    }
    /**
     * 初始化用户界面
     * @return 用户输入的用户名和密码
     */
    private static Map<String, String> initUI() {
        Scanner s = new Scanner(System.in);
        System.out.println("请输入用户名：");
        String userName = s.nextLine();
        System.out.println("请输入密码：");
        String userPwd = s.nextLine();
        Map<String,String> userLoginInfo = new HashMap<>();
        userLoginInfo.put("userName",userName);
        userLoginInfo.put("userPwd",userPwd);
        return userLoginInfo;
    }
}

3、结果显示；

image
image

4、阻止SQL注入

3.png

private static Map<String, String> initUI() {
Scanner s = new Scanner(System.in);
System.out.println("请输入用户名：");
String userName = s.nextLine();
System.out.println("请输入密码：");
String userPwd = s.nextLine();
Map<String,String> userLoginInfo = new HashMap<>();
userLoginInfo.put("userName",userName);
userLoginInfo.put("userPwd",userPwd);
return userLoginInfo;
}