一文搞懂Java JDBC中的SQL注入问题

package cn.bdqn.demo03;
​
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;
​
public class Login {
​
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        
        //创建Scanner类对象，从控制台获取用户名和密码数据
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入用户名：");
        String user = sc.nextLine();//使用nextLine()方法获取字符串
        System.out.println("请输入密码：");
        String pwd = sc.nextLine();//使用nextLine()方法获取字符串
        
        //1、注册驱动
        Class.forName("com.Mysql.jdbc.Driver");
        //2、获取连接对象
        String url = "jdbc:mysql://127.0.0.1:3306/java221804";
        String dbuser = "root";
        String pssWord = "123456";
        Connection connection = DriverManager.getConnection(url, dbuser, pssword);
        //3、获取发送SQL语句的对象
        Statement statement =connection.createStatement();
        //编写SQL语句
        String sql = "SELECT * FROM user WHERE username='"+user+"' AND pssword = '"+pwd+"';";
        //4、执行SQL语句
        ResultSet resultSet=statement.executeQuery(sql);
        if(resultSet.next()){
            System.out.println("用户名和密码正确，登录成功");
        }else{
            System.out.println("用户名或密码不正确，登录失败");
        }
        //6、关闭资源
        resultSet.close();
        statement.close();
        connection.close();
        sc.close();
    }
}

SELECT * FROM user WHERE username='abc' or 1=1;#' AND pssword = '123';

package cn.bdqn.demo02;
​
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Scanner;
​
public class PreparedStatementDemo01 {
​
    public static void main(String[] args) throws ClassNotFoundException,SQLException {
​
        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 pwd = sc.nextLine();
​
        // 1、注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        // 2、获得连接
        String url = "jdbc:mysql://localhost:3306/java2217";
        String user = "root";
        String pssword = "123456";
        Connection connection = DriverManager.getConnection(url, user, pssword);
        // 3、获取发送SQL对象
        String sql = "select * from user where userName = ? and pssword=?;";
        PreparedStatement preparedStatement = connection.prepareStatement(sql);
        // 4、绑定参数，有多少个?绑定多少个参数值
        preparedStatement.setString(1, userName);
        preparedStatement.setString(2, pwd);
        // 5、执行SQL语句，并处理结果
        ResultSet resultSet = preparedStatement.executeQuery();
        if (resultSet.next()) {
            System.out.println("用户名和密码正确，登录成功");
        } else {
            System.out.println("用户名或密码错误，登录失败");
        }
        // 6、释放资源:与关闭流的方式一样，先开的后关，后开的先关
        resultSet.close();
        preparedStatement.close();
        connection.close();
        sc.close();
    }
}

public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.print("升序输入asc，降序输入desc：");
        String order = s.nextLine();
        // 定义变量
        Connection connection = null;
        Statement statement = null;
        ResultSet rs = null;
 
 
        try {
            // 注册驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            // 获取连接
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/MyTest","root", "********");
            // 获取数据库操作对象
            statement = connection.createStatement();
            // 执行sql
            String sql = "select * from emp order by sal " + order;
            rs = statement.executeQuery(sql);
            // 处理查询结果集
            while(rs.next()){
                String ename = rs.getString("ename");
                double sal = rs.getDouble("sal");
                System.out.println("姓名：" + ename + ",薪资：" + sal);
            }
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        } finally {
            // 释放资源
            if (rs != null) {
                try {
                    rs.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();
                }
            }
        }
    }