Question

I tried

Thread.setDefaultUncaughtExceptionHandler...

in the main, and also in the start(Stage primaryStage) method. It ain’t working.
I also tried

public static void main(String[] args) {
 try {
  launch(args);
 }catch(Throwable t) {
  System.out.println(t.getMessage);
 }
}

Exception stack trace.

at javafx.concurrent.Task$TaskCallable$2.run(Task.java:1251) at
com.sun.javafx.application.PlatformImpl$3.run(PlatformImpl.java:141)
at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method) at
com.sun.glass.ui.gtk.GtkApplication$1$1.run(GtkApplication.java:56)
at java.lang.Thread.run(Thread.java:662)

Thanks for helping.

Answer 1

If you check the code for Platform.runLater() (see below), you will see that the exceptions are swallowed (lines 146 / 147), so a default uncaught exception handler won’t be able to catch them – based on that piece of code, I don’t think you have any options but to include try/catch blocks in your runnables.

Note that this issue has been reported (requires login – registration is free) and should be fixed in Lombard (= Java FX 8.0 to be released with Java 8 next year).

You could alternatively create a utility method and call

Platform.runLater(getFxWrapper(yourRunnable));

public static Runnable getFxWrapper(final Runnable r) {
    return new Runnable() {

        @Override
        public void run() {
            try {
                r.run();
            } catch (Exception e) {
                //here you probably want to log something
                System.out.println("Found an exception");
            }
        }
    };
}

Code of Platform.runLater:

  120     private static void runLater(final Runnable r, boolean exiting) {
  121         if (!initialized.get()) {
  122             throw new IllegalStateException("Toolkit not initialized");
  123         }
  124 
  125         pendingRunnables.incrementAndGet();
  126         waitForStart();
  127 
  128         if (SystemProperties.isDebug()) {
  129             Toolkit.getToolkit().pauseCurrentThread();
  130         }
  131 
  132         synchronized (runLaterLock) {
  133             if (!exiting && toolkitExit.get()) {
  134                 // Don't schedule a runnable after we have exited the toolkit
  135                 pendingRunnables.decrementAndGet();
  136                 return;
  137             }
  138 
  139             Toolkit.getToolkit().defer(new Runnable() {
  140                 @Override public void run() {
  141                     try {
  142                         r.run();
  143                         pendingRunnables.decrementAndGet();
  144                         checkIdle();
  145                     } catch (Throwable t) {
  146                         System.err.println("Exception in runnable");
  147                         t.printStackTrace();
  148                     }
  149                 }
  150             });
  151         }
  152     }