Question

SwingWorker lets you prepare some data in a background Thread and then use it in EDT. I am looking for a utility that does the opposite: Prepare data in EDT, and then pass it to a background Thread.

If you’re curious, the use case is saving state of a JTable to disk (column order, size, etc.). I need to talk to its model in EDT, but don’t want to write to disk from this thread.

Something like:

void saveCurrentState(final Table table) {
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            TableColumns state = dumpState(table);
            saveToDisk(table.getTableKey(), state);
        }
    });
}

dumpState() needs to run in EDT. saveToDisk() should NOT run in EDT. The whole thing is deliberately wrapped in invokeLater(), and I cannot replace it with invokeAndWait().

Answer 1

You’re probably looking for ExecutorService. Get one using Executors.newCachedThreadPool() – or the other newXXX() methods, but that one should be okay for most uses.

That said, I believe this is something you can do with SwingWorker as well. Just prepare your data in the event handler before you create a SwingWorker – you’re already on the EDT there. If you need to initiate this from a non-EDT thread, prepare the data using SwingUtilities.invokeAndWait(), and then spin off another thread to do the writing (or do it in the same non-EDT thread you started with.)

SwingWorker and ExecutorService provide the same basic service – spin off some work into a background thread without having to manage its lifecycle explicitly. SwingWorker has a convenient method of communicating with the EDT without using invokeLater() all over the place that you don’t need to use, and ExecutorService supports futures as a more general (non-Swing-specific) way of communicating with asynchronous task. For a fire-and-forget use case as yours both are fine.