Java: Updating JTable with lots of rows in the background

Question

I am writing a simple Java Swing utility that will read messages from an MQ JMS server and display them in a JTable.

private void getMessages() {
        try {
            if (null != Queue) {
                Queue.close();  //Close previous queue connection if there is one.
            }
            Queue = new MQQueue(QueueManager, tableQueues.getValueAt(tableQueues.getSelectedRow(), 1).toString(), MQConstants.MQOO_INPUT_SHARED | MQConstants.MQOO_BROWSE | MQConstants.MQOO_OUTPUT, queueManager, null, null);
            int count = 0;
            modelMessages.setRowCount(0);
            MQGetMessageOptions getOptions = new MQGetMessageOptions();
            getOptions.options = MQConstants.MQGMO_BROWSE_FIRST;
            ArrayList<Object[]> rows = new ArrayList<Object[]>();
            while(true) {
                if (count > 0) {
                    getOptions.options = MQConstants.MQGMO_BROWSE_NEXT;
                }
                MQMessage message = new MQMessage();
                try {
                    Queue.get(message, getOptions);
                    byte[] b = new byte[message.getMessageLength()];
                    message.readFully(b);
                    rows.add(new Object[]{count + 1, new String(b)});
                    modelMessages.addRow(new Object[]{count + 1, new String(b)});
                    message.clearMessage();
                    count++;
                }
                catch (IOException e) {
                    break;
                }
                catch (MQException e) {
                    if (e.completionCode == 2 && e.reasonCode == MQConstants.MQRC_NO_MSG_AVAILABLE) {
                        break;
                    }
                }
            }
            modelMessages.fireTableDataChanged();
        } catch (MQException e) {
            txtMessage.setText("MQJE001: Completion Code '" + e.completionCode + "', Reason '" + e.reasonCode + "'.");
            modelMessages.setRowCount(0);
            modelMessages.fireTableDataChanged();
        }
    }

This works well for smaller queues but for large queues, it takes a while to populate this table and in the meantime, the Swing application is frozen so I am investigating ways to populate the JTable in the background while keeping not only the application but the JTable itself usable and scrollable during this.

I'm not very familiar with threading and I've tried a few things such wrapping some parts in SwingUtilities.invokeLater and implementing doInBackground() but nothing has seemed to work. Could someone please point me in the right direction of how to proceed with this?

EDIT

Based on the replies below, here is the solution:

public class GetMessagesWorker extends SwingWorker<DefaultTableModel, Object[]> {

    //http://stackoverflow.com/questions/22072480/java-updating-jtable-with-lots-of-rows-in-the-background#

    private final DefaultTableModel model;

    public GetMessagesWorker(DefaultTableModel model){
        this.model = model;
    }

    @Override
    protected DefaultTableModel doInBackground() throws Exception {
        try {
            if (null != Queue) {
                Queue.close();  //Close previous queue connection if there is one.
            }
            Queue = new MQQueue(QueueManager, tableQueues.getValueAt(tableQueues.getSelectedRow(), 1).toString(), MQConstants.MQOO_INPUT_SHARED | MQConstants.MQOO_BROWSE | MQConstants.MQOO_OUTPUT, queueManager, null, null);
            int count = 0;
            modelMessages.setRowCount(0);
            MQGetMessageOptions getOptions = new MQGetMessageOptions();
            getOptions.options = MQConstants.MQGMO_BROWSE_FIRST;
            while(true) {
                if (count > 0) {
                    getOptions.options = MQConstants.MQGMO_BROWSE_NEXT;
                }
                MQMessage message = new MQMessage();
                try {
                    Queue.get(message, getOptions);
                    byte[] b = new byte[message.getMessageLength()];
                    message.readFully(b);
                    Object[] row = {count + 1, new String(b)};
                    publish(row);
                    message.clearMessage();
                    count++;
                    if (isCancelled()) {
                        modelMessages.setRowCount(0);
                        count = 0;
                        message.clearMessage();
                        return model;
                    }
                }
                catch (IOException e) {
                    break;
                }
                catch (MQException e) {
                    if (e.completionCode == 2 && e.reasonCode == MQConstants.MQRC_NO_MSG_AVAILABLE) {
                        break;
                    }
                }
            }
            //modelMessages.fireTableDataChanged();
        } catch (MQException e) {
            txtMessage.setText("MQJE001: Completion Code '" + e.completionCode + "', Reason '" + e.reasonCode + "'.");
            modelMessages.setRowCount(0);
            modelMessages.fireTableDataChanged();
        }
        return model;
    }

    @Override
    protected void process(List<Object[]> chunks){
        for(Object[] row : chunks){
            model.addRow(row);
        }
    }

}

And here is the listener:

    tableQueues = new JTable(modelQueues);
    tableQueues.getSelectionModel().addListSelectionListener(new ListSelectionListener() {
        public void valueChanged(ListSelectionEvent e) {
            if (!e.getValueIsAdjusting()) {
                txtMessage.setText("");
                if (tableQueues.getSelectedRow() > -1) {
                    gmw.cancel(false);
                    gmw = new GetMessagesWorker(modelMessages);
                    gmw.execute();
                }
            }
        }
    });

Answer 1

When doing threading in Swing you need to understand that you have to do the work in the background thread but any UI updates have to be done in the Swing thread.

That means you should create a thread to fetch the messages. When you have one (or more), then use SwingUtilities to synchronize with the Swing thread and update the table.

In the code snippet above, that means you need to use SwingUtilities every time that you invoke a method of modelMessages, txtMessage, etc.

Since that's pretty expensive, you will usually collect, say, 10 new rows in list and then add them all at once using a single call to SwingUtilities.invokeLater().

Answer 2

This is due to Swing architecture. You must understand that the same thread where your listener is being executed is responsible for far more things (for example, refresh your UI).

I would use in your case a SwingWorker. This is a kind of Swing-specific background thread with special features to safely send updates to your UI as it executes its long task. You would do there your long task in background and call publish() for every relevant result it retrieves. Every time publish() is called, your process() method would be called (sending an update to the main thread under the hood), there you could update your table model.

Here you can find more information on SwingWorker:

http://docs.oracle.com/javase/tutorial/uiswing/concurrency/worker.html