Question

Each time a back-end message comes I add it to JList and JList is being refreshed using fireIntervalAdded. The problem is that in one second 20 messages may arrive and each one of them will call fireIntervalAdded. What I would like to do is to stack all messages in List and send one big stack of data to JList. My current solution does not seem to work, it always sends one message instead of one big stack:

    private class StackingListener implements MessageListener {
    private List<Message> messages = new LinkedList<Message> ();
    private int waiting = 0;
    @Override
    public void messageReceived(MessageEvent event) {
        stackData(event.getData());
    }

    private void stackData(Message data) {
        messages.add(data);
        if (waiting <= 0) {
            waiting = 3;
            new Thread(new Runnable() {
                @Override
                public void run() {
                    while(--waiting > 0) {
                        try {
                            Thread.sleep(500);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    List<Message> list = new ArrayList<Message>(messages);
                    messages.clear();
                    logger.info("Adding list with size of " + list.size());
                    controller.getListModel().addFullElements(list);
                }
            }).run();
        } else {
            waiting = 3;
        }
    }
}

I think I’m doing something very wrong. The idea of this code is to stack up messages while Thread is sleeping. But seems like Thread.sleep stops everything, not only the current thread.

Thanks

Answer 1

You are using Thread.run() which just calls the run() method in the current thread. What you intended to use was Thread.start() creates a thread and call run() in that new thread.

However I wouldn’t structure the code like this at all. I believe a simpler apporach is to use a queue.

class StackingListener implements MessageListener, Runnable {
    private final BlockingQueue<Message> messages = new LinkedBlockingDeque<Message>();
    private final ScheduledExecutorService service = Executors.newSingleThreadScheduledExecutor(); {
        service.scheduleAtFixedRate(this, 500, 500, TimeUnit.MILLISECONDS);
    }

    @Override
    public void messageReceived(MessageEvent event) {
        messages.add(event.getData());
    }

    @Override
    public void run() {
        final List<Message> list = new ArrayList<Message>();
        messages.drainTo(list);

        logger.info("Adding list with size of " + list.size());
        // add to the GUI component in a thread safe manner.
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                controller.getListModel().addFullElements(list);
            }
        });
    }

    public void stop() {
        service.shutdown();
    }
}