Last week, I updated my local copy of the SwingX source code, modifying SwingXUtilities to inlcude an invokeLater and an invokeAndWait that support return values.  I plan on checking in that code sometime today.  In one of those strange coincidences, Swing links of the week pointed me to Jan Kotek's post: SwingUtilities.invokeAndWait with return value.  It's a good article, but my solution was different.

To obtain a value, we will use a Callable (basically a Runnable that supports return values).  I use FutureTask to wrap my Callable.  A FutureTask is a Runnable, so it may be directly submitted to either of the core SwingUtilities invoke methods.  The get method in FutureTask is the method that actually returns the value (it is blocking).  So, we begin by creating a new invokeLater method to wrap SwingUtilities.invokeLater.

public static <T> FutureTask<T> invokeLater(Callable<T> callable) {
    FutureTask<T> task = new FutureTask<T>(callable);
    return task;

This method will not block the calling thread and now you have access to the FutureTask, enabling you to get the value (at some future point).  Building on that, we can create a method that blocks, just as SwingUtilities.invokeAndWait does.

public static <T> T invokeAndWait(Callable<T> callable) throws InterruptedException,
        InvocationTargetException {
    try {
        //blocks until future returns
        return invokeLater(callable).get();
    } catch (ExecutionException e) {
        Throwable t = e.getCause();
        if (t instanceof RuntimeException) {
            throw (RuntimeException) t;
        } else if (t instanceof InvocationTargetException) {
            throw (InvocationTargetException) t;
        } else {
            throw new InvocationTargetException(t);

By using FutureTask.get, we can create a blocking method that waits for the return value by calling get.  Since it returns wrapped exceptions, we unwrap them and pass them on as appropriate.