NullPointerException on resultSet尝试将数据加载到TableView中的日期

Question

So im getting this NPE whenever im trying to return an ArrayList object into an FXCOLLECTIONS list.

Here is the Code.

Method return the al to FXCOLLECTIONS.

public ArrayList<MeetBooking> selectMeetBookings()
{
    ArrayList<MeetBooking> meetBookingArrayList = new ArrayList<>();
    System.out.println("Trying to select from table meetBooking");

    try
    {
        //Query the database and storing the result in an object of type ResultSet
        sqlString = "SELECT * FROM CPC.meetBooking ORDER BY bookingID ASC";
        rs = stmt.executeQuery(sqlString);

        //Use the methods of class ResultSet in a loop
        // to display all of the data in the result
        while (rs.next())
        {
            int id = rs.getInt("bookingID");
            Date bookingDateTime = rs.getDate("bookingDateTime");
            System.out.println(bookingDateTime.toString());
            int empID = rs.getInt("employeeID");
            String bookingcmnt = rs.getString("bookingComment");



            MeetBooking meetBooking = new MeetBooking();

            meetBooking.setBookingID(id);
            meetBooking.setBookingDate(bookingDateTime.toString());
            meetBooking.setEmployeeID(empID);
            meetBooking.setBookingComment(bookingcmnt);
            meetBookingArrayList.add(meetBooking);
        }

    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
    return meetBookingArrayList;
}

    Public Class MeetBooking
    //Method to set a date as a string utilises Stringproperty and                      //simplestringproperty
    public void setBookingDate(String value)
    {
    bookingDate.set(value);
    }

    //Controller access to first method
    public ArrayList<MeetBooking> getMeetBookings()
    {
    return dbcon.selectMeetBookings();
    }


    // UI access to controller.getMeetBooks
    meetBookingObservableList =      FXCollections.observableArrayList(controller.getMeetBookings());

Im not quite sure how to solve this, but i think the Date is the culprit. However I've been debugging this for a long time and need your expertise.

Answer 1

One potential reason for the NPE is that your database can contain Null values in some of your columns.

If you have Nulls in the bookingDateTime or the employeeID columns, then you will get an exception in one of the following lines:

Date bookingDateTime = rs.getDate("bookingDateTime");
System.out.println(bookingDateTime.toString());
int empID = rs.getInt("employeeID");

If I remember my Java, the Date class can contain a null. However, if the value is null, then bookingDateTime.toString() will attempt to convert the Null to string. A Null does not have a method, so you get that NullPointerException.

Also, an int cannot store Nulls, so you have a similar issue when attempting to force a Null into empID.