如何根据用户输入（扫描仪）获取 SQL 准备语句

Posted 2023-03-27

【中文标题】如何根据用户输入（扫描仪）获取 SQL 准备语句

【英文标题】：How to get SQL prepared statement based on user input (scanner)

【发布时间】：2019-05-10 09:30:12

【问题描述】：

我在创建准备好的语句时遇到困难，该语句选择并打印出满足条件的行：

SELECT ReservationStartDate, ReservationEndDate FROM treservations WHERE ReservationStartDate< **?** AND ReservationEndDate> **?**

“？”用户输入 - 字符串，例如 2019-07-09 和 2019-08-16

我可以通过以下方法选择*：

public static List<Reservation> getAllReservation()
        List<Reservation> reservationsList = new ArrayList<>();
        String sql = "SELECT * FROM `treservations`";
        try
            PreparedStatement ps = ConnectorDB.connection.prepareStatement(sql);
            ResultSet resultSet = ps.executeQuery();
            while (resultSet.next())
                Reservation reservation = new Reservation();
                reservation.setReservationID(resultSet.getInt("ReservationID"));
                reservation.setCarID(resultSet.getInt("CarID"));
                reservation.setReservationStartDate(resultSet.getString("ReservationStartDate"));
                reservation.setReservationEndDate(resultSet.getString("ReservationEndDate"));
                reservation.setPesel(resultSet.getString("Pesel"));
                reservationsList.add(reservation);
            
        catch (SQLException e)
            e.printStackTrace();
        
        return reservationsList;
    

例如，根据扫描仪的用户输入插入新行：

public static List<Reservation> getAllReservation()
        List<Reservation> reservationsList = new ArrayList<>();
        String sql = "SELECT * FROM `treservations`";
        try
            PreparedStatement ps = ConnectorDB.connection.prepareStatement(sql);
            ResultSet resultSet = ps.executeQuery();
            while (resultSet.next())
                Reservation reservation = new Reservation();
                reservation.setReservationID(resultSet.getInt("ReservationID"));
                reservation.setCarID(resultSet.getInt("CarID"));
                reservation.setReservationStartDate(resultSet.getString("ReservationStartDate"));
                reservation.setReservationEndDate(resultSet.getString("ReservationEndDate"));
                reservation.setPesel(resultSet.getString("Pesel"));
                reservationsList.add(reservation);
            
        catch (SQLException e)
            e.printStackTrace();
        
        return reservationsList;
    

问题是如何结合这两种方法，并能够根据用户扫描仪输入选择数据库中的行（然后打印出来）。

我的想法： 1. 我们根据用户输入创建预订对象

    public static Reservation clientReservationMenuInput()
        Scanner scanner = new Scanner(System.in);
        String regData = "\\d4-\\d2-\\d2";
        System.out.println("2 Reservation start date (YYYY-MM-DD) ");
        String ReservationStartDate;
        while (!(ReservationStartDate=scanner.next()).matches(regData))
            System.out.printf("Date format not correct, Please try once again\n");
        
        System.out.println("3 Reservation end date (YYYY-MM-DD) ");
        String ReservationEndDate;
        while (!(ReservationEndDate=scanner.next()).matches(regData))
            System.out.printf("Date format not correct, Please try once again\n");
        
        Reservation reservation = new Reservation();
        reservation.setReservationStartDate(ReservationStartDate);
        reservation.setReservationEndDate(ReservationEndDate);
        return reservation;
    

创建的对象是checkDatesForReservation方法的参数 SQL 哪里有两个参数“？”表示来自用户输入的日期 我需要 while 循环来查找所有行 最后我需要返回一个列表

    public static List<Reservation> checkDatesForReservation(Reservation reservation)
        List<Reservation> reservationList = new ArrayList<>();
        String sql2= "SELECT ReservationStartDate, ReservationEndDate FROM treservations WHERE ReservationStartDate=? AND ReservationEndDate= ?";
        try
            PreparedStatement ps = ConnectorDB.connection.prepareStatement(sql2);
            ResultSet resultSet = ps.executeQuery();
            while (resultSet.next())
                ps.setString(1,reservation.getReservationStartDate());
                ps.setString(2,reservation.getReservationEndDate());
                reservationList.add(reservation);
            
        catch (SQLException e)
            e.getStackTrace();
        
        return reservationList;
    

【问题讨论】：

问题是什么？你有什么错误吗？

【参考方案1】：

请参考JDBC PreparedStatement example – Select list of the records

 public static List<Reservation> checkDatesForReservation(Reservation reservation)
        Reservation reservation = null;
        List<Reservation> reservationList = new ArrayList<>();
        String sql2= "SELECT ReservationStartDate, ReservationEndDate FROM treservations WHERE ReservationStartDate=? AND ReservationEndDate= ?";
        try
            PreparedStatement ps = ConnectorDB.connection.prepareStatement(sql2);
            ps.setString(1,reservation.getReservationStartDate());
            ps.setString(2,reservation.getReservationEndDate());
            ResultSet resultSet = ps.executeQuery();
            while (resultSet.next())
               reservation = new Reservation();
               reservation.setReservationStartDate(rs.getString("ReservationStartDate"));
               reservation.setReservationEndDate(rs.getString("ReservationEndDate"));
               reservationList.add(reservation);
            
        catch (SQLException e)
            e.getStackTrace();
        
        return reservationList;
    

【讨论】：

谢谢。但由于某种原因，我得到了 reservationList - 是空的。但现在我对这个解决方案很满意，需要仔细研究一下。

【参考方案2】：

执行语句前需要设置参数。

        PreparedStatement ps = ConnectorDB.connection.prepareStatement(sql2);
        ps.setString(1,reservation.getReservationStartDate());
        ps.setString(2,reservation.getReservationEndDate());
        ResultSet resultSet = ps.executeQuery();
        while (resultSet.next())
            reservationList.add(reservation);