How do I update a JTable based on a notification received from a long-running task in other thread?

Question

I've an Observer TableModel which listens to some changes, performed in the database, and when so the update method below is called. My problem is, how should I prevent errors like:

java.lang.IndexOutOfBoundsException: Index: 1, Size: 1
at java.util.ArrayList.RangeCheck(ArrayList.java:547)
at java.util.ArrayList.set(ArrayList.java:337)
at com.mysimpatico.memoplatform.persistenceui.MeaningsViewerTopComponent$DefaultTableModelImpl.update(MeaningsViewerTopComponent.java:108)

I don't see how SwingWorker would help. I've the long-running database task being performed in a separate thread, but this calls upon a method (database persisting) in an Observable class which notifies observers.

@Override
        public void update(Observable o, final Object arg) {
            final Meaning meng = (Meaning) arg;
            final int row;
            final boolean insert;
            synchronized (mengs) {
                if (mengs.contains(meng)) {
                    row = meng.getObjId();
                    mengs.set(row, meng);
                    insert = false;
                } else {
                    row = mengs.size();
                    mengs.add(row, meng); //last
                    insert = true;
                }
                try {
                    SwingUtilities.invokeAndWait(new Runnable() {

                    @Override
                    public void run() {
                        if (insert) {
                            fireTableRowsInserted(row, row);
                        } else {
                            fireTableRowsUpdated(row, row);
                        }
                    }
                });
            } catch (InterruptedException ex) {
                Exceptions.printStackTrace(ex);
            } catch (InvocationTargetException ex) {
                Exceptions.printStackTrace(ex);
            }
        }
    }

Answer 1

One option is using a org.jdesktop.application.Task. You will need to pass the TableModel to the Task and then so a simple TableModel.insert call.

Note: The task is just a nice wrapper around a Thread.

Answer 2

Despite firing insert / update TableModelEvents on the event dispatch thread you're actually updating the TableModel on whichever thread is performing the notification of the database update. This is dangerous as it means:

• The event dispatch thread could potential see the TableModel in an inconsistent state.
• The event dispatch thread could be attempting to render the TableModel as the notification thread is altering it.

The solution should (in theory) simply be a case of moving your call to SwingUtilities.invokeAndWait to outside the block of code that begins: synchronized(mengs). Also, once you've done this you can actually removed the synchronized keyword entirely as all access to your model will be done on the EDT.

As an aside I would avoid using the Observer / Observable classes (for more information see my answer to this question); far better to define domain-specific listener interfaces and event classes (that subclass java.util.EventObject).

Answer 3

Are your indexes correct?

java.lang.IndexOutOfBoundsException: Index: 1, Size: 1 

The above statement says you only have one entry in the array list. I can't tell if your code is an "add" or an "update". But remember that ResultSet indexes are 1 based not 0 based so maybe you need to subtract 1 from all your row values?