如何根据从其他线程中长时间运行的任务收到的​​通知更新JTable？

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

Despite firing insert / update TableModelEvent s 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 2

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?

Answer 3

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.