JDBC 工具類練習

一、需求

1. 通過鍵盤錄入用戶名和密碼
2. 判斷用戶是否登錄成功

select * from user where username = "" and password = "";
如果這個sql有查詢結果，則成功，反之，則失敗

二、代碼實現

數據庫存儲：

jdbc.properties 配置:

url = jdbc://mysql:///student
user = root
password = root
driver = com.mysql.jdbc.Driver

JDBCUtils.java ：

/**
 * JDBC工具類
 */
public class JDBCUtils {
    private static String url;
    private static String user;
    private static String password;
    private static String driver;
    /**
     * 文件的讀取，只需要讀取一次即可拿到這些值。使用靜態代碼塊
     */
    static{
        //讀取資源文件，獲取值。

        try {
            //1. 創建Properties集合類。
            Properties pro = new Properties();

            //獲取src路徑下的文件的方式--->ClassLoader 類加載器
            ClassLoader classLoader = JDBCUtils.class.getClassLoader();
            URL res  = classLoader.getResource("jdbc.properties");
            String path = res.getPath();

            //2. 加載文件
            pro.load(new FileReader(path));

            //3. 獲取數據，賦值
            url = pro.getProperty("url");
            user = pro.getProperty("user");
            password = pro.getProperty("password");
            driver = pro.getProperty("driver");
            //4. 註冊驅動
            Class.forName(driver);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    /**
     * 獲取連接
     * @return 連接對象
     */
    public static Connection getConnection() throws SQLException {

        return DriverManager.getConnection(url, user, password);
    }

    /**
     * 釋放資源
     * @param stmt
     * @param conn
     */
    public static void close(Statement stmt,Connection conn){
        if( stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if( conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    /**
     * 釋放資源
     * @param stmt
     * @param conn
     */
    public static void close(ResultSet rs,Statement stmt, Connection conn){
        if( rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if( stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if( conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

JdbcDemo.java：

public class JDBCDemo {

    public static void main(String[] args) {
        //1.鍵盤錄入，接受用戶名和密碼
        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 password = sc.nextLine();
        //2.調用方法
        boolean flag = new JDBCDemo9().login2(username, password);
        //3.判斷結果，輸出不同語句
        if(flag){
            //登錄成功
            System.out.println("登錄成功！");
        }else{
            System.out.println("用戶名或密碼錯誤！");
        }
    }
    /**
     * 登錄方法
     */
    public boolean login(String username ,String password){
        if(username == null || password == null){
            return false;
        }
        //連接數據庫判斷是否登錄成功
        Connection conn = null;
        Statement stmt =  null;
        ResultSet rs = null;
        //1.獲取連接
        try {
            conn =  JDBCUtils.getConnection();
            //2.定義sql
            String sql = "select * from user where username = '"+username+"' and password = '"+password+"' ";
            System.out.println(sql);
            //3.獲取執行sql的對象
            stmt = conn.createStatement();
            //4.執行查詢
            rs = stmt.executeQuery(sql);
            //5.判斷
           /* if(rs.next()){//如果有下一行，則返回true
                return true;
            }else{
                return false;
            }*/
           return rs.next();//如果有下一行，則返回true

        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs,stmt,conn);
        }
        return false;
    }
}

這裏需要注意添加 username 和 password 之後 sql 的寫法：

String sql = "select * from user where username = '' and password = ''";
然後將傳入的參數 user 和 password 寫入：
String sql = "select * from user where username = '"+username+"' and password = '"+password"'";