package cn.bdqn.demo03;
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import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;
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public class Login {
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    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        
        //創(chuàng)建Scanner類對象，從控制臺(tái)獲取用戶名和密碼數(shù)據(jù)
        Scanner sc = new Scanner(System.in);
        System.out.println("請輸入用戶名：");
        String user = sc.nextLine();//使用nextLine()方法獲取字符串
        System.out.println("請輸入密碼：");
        String pwd = sc.nextLine();//使用nextLine()方法獲取字符串
        
        //1、注冊驅(qū)動(dòng)
        Class.forName("com.mysql.jdbc.Driver");
        //2、獲取連接對象
        String url = "jdbc:mysql://127.0.0.1:3306/java221804";
        String dbuser = "root";
        String pssword = "123456";
        Connection connection = DriverManager.getConnection(url, dbuser, pssword);
        //3、獲取發(fā)送SQL語句的對象
        Statement statement =connection.createStatement();
        //編寫SQL語句
        String sql = "SELECT * FROM user WHERE username='"+user+"' AND pssword = '"+pwd+"';";
        //4、執(zhí)行SQL語句
        ResultSet resultSet=statement.executeQuery(sql);
        if(resultSet.next()){
            System.out.println("用戶名和密碼正確，登錄成功");
        }else{
            System.out.println("用戶名或密碼不正確，登錄失敗");
        }
        //6、關(guān)閉資源
        resultSet.close();
        statement.close();
        connection.close();
        sc.close();
    }
}

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

package cn.bdqn.demo02;
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import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Scanner;
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public class PreparedStatementDemo01 {
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    public static void main(String[] args) throws ClassNotFoundException,SQLException {
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        Scanner sc = new Scanner(System.in);
        System.out.println("請輸入用戶名：");
        String userName = sc.nextLine();
        System.out.println("請輸入密碼：");
        String pwd = sc.nextLine();
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        // 1、注冊驅(qū)動(dòng)
        Class.forName("com.mysql.jdbc.Driver");
        // 2、獲得連接
        String url = "jdbc:mysql://localhost:3306/java2217";
        String user = "root";
        String pssword = "123456";
        Connection connection = DriverManager.getConnection(url, user, pssword);
        // 3、獲取發(fā)送SQL對象
        String sql = "select * from user where userName = ? and pssword=?;";
        PreparedStatement preparedStatement = connection.prepareStatement(sql);
        // 4、綁定參數(shù)，有多少個(gè)?綁定多少個(gè)參數(shù)值
        preparedStatement.setString(1, userName);
        preparedStatement.setString(2, pwd);
        // 5、執(zhí)行SQL語句，并處理結(jié)果
        ResultSet resultSet = preparedStatement.executeQuery();
        if (resultSet.next()) {
            System.out.println("用戶名和密碼正確，登錄成功");
        } else {
            System.out.println("用戶名或密碼錯(cuò)誤，登錄失敗");
        }
        // 6、釋放資源:與關(guān)閉流的方式一樣，先開的后關(guān)，后開的先關(guān)
        resultSet.close();
        preparedStatement.close();
        connection.close();
        sc.close();
    }
}

public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.print("升序輸入asc，降序輸入desc：");
        String order = s.nextLine();
        // 定義變量
        Connection connection = null;
        Statement statement = null;
        ResultSet rs = null;
 
 
        try {
            // 注冊驅(qū)動(dòng)
            Class.forName("com.mysql.cj.jdbc.Driver");
            // 獲取連接
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/MyTest","root", "********");
            // 獲取數(shù)據(jù)庫操作對象
            statement = connection.createStatement();
            // 執(zhí)行sql
            String sql = "select * from emp order by sal " + order;
            rs = statement.executeQuery(sql);
            // 處理查詢結(jié)果集
            while(rs.next()){
                String ename = rs.getString("ename");
                double sal = rs.getDouble("sal");
                System.out.println("姓名：" + ename + ",薪資：" + sal);
            }
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        } finally {
            // 釋放資源
            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();
                }
            }
        }
    }