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IllegalStateException when using JavaFX Alert in init() because not on FX application thread

Using this approach I am trying to implement an application preloader for my JavaFX application. I want to load some heavy stuff in init() which may throw an exception and then continue with start(). To handle the exceptions I am showing an alert using new Alert(AlertType.ERROR).showAndWait(); that shows some details to the user.
public class Test extends Application {
#Override
public void init() throws Exception {
try {
// dome some heavy stuff here
throw new Exception();
} catch (Exception e) {
new Alert(AlertType.ERROR).showAndWait();
Platform.exit();
}
}
#Override
public void start(Stage primaryStage) {
StackPane root = new StackPane();
primaryStage.setScene(new Scene(root, 300, 250));
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
But this results in the alert not showing up and generating the following stack trace (see full stacktrace here):
Exception in Application init method
java.lang.reflect.InvocationTargetException
...
Caused by: java.lang.RuntimeException: Exception in Application init method
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:895)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:195)
at java.base/java.lang.Thread.run(Thread.java:830)
Caused by: java.lang.IllegalStateException: Not on FX application thread; currentThread = JavaFX-Launcher
at javafx.graphics/com.sun.javafx.tk.Toolkit.checkFxUserThread(Toolkit.java:291)
...
at javafx.controls/javafx.scene.control.Alert.<init>(Alert.java:222)
at src/gui.Test.init(Test.java:18)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:824)
... 2 more
Exception running application gui.Test
However my approach works fine if I move the howl code from init() to start().

In the past I've been able to solve this kind of issues with wrapping the logic in a Platform.runLater() call. ie:
try {
[...]
} catch (Exception e) {
Platform.runLater(new Runnable() {
#Override public void run() {
new Alert(AlertType.ERROR).showAndWait();
Platform.exit();
});
}
I use this approach every time I need to do some work that's not directly related to what's going on in the interface.
As taken from the wiki :
public static void runLater(Runnable runnable)
Parameters:
runnable - the Runnable whose run method will be executed on the JavaFX Application Thread

JavaFX with Junit

I would like to test methods that have JavaFX scene elements like TextField or DatePicker. I found here How do you unit test a JavaFX controller with JUnit how to run test for JavaFX app and it works fine for me if I have just one test class where Thread is initialized. But what about if I have two classes? I am not able to initialize the same thread with launch method because exception will be thrown. If I will not create thread in second test class there is also another exception. Below you can find test classes and stack trace. I was also thinking about stopping this thread in method with #AfterClass annotation and then starting it in second class again but I do not think it is possible. Does anyone can help me?
FirstTestClass
#RunWith(PowerMockRunner.class)
#PrepareForTest({TextField.class, DatePicker.class})
public class FirstTestClass {
#BeforeClass
public static void javaFXInitializer() throws SQLException, InterruptedException {
Thread thread = new Thread("JavaFX Init Thread") {
public void run() {
Application.launch(Main.class);
}
};
thread.setDaemon(true);
thread.start();
Thread.sleep(5000);
}
#Test
public void firstTest() {
TextField textFieldMock = mock(TextField.class);
DatePicker datePickerMock = mock(DatePicker.class);
TestClass objectUnderTest = new TestClass();
when(textFieldMock.getText()).thenReturn("2000");
when(datePickerMock.getValue()).thenReturn(LocalDate.of(1992,1,1));
//rest of code to test
}
}
SecondTestClass
#RunWith(PowerMockRunner.class)
#PrepareForTest({TextField.class, DatePicker.class})
public class SecondTestClass {
#BeforeClass
public static void javaFXInitializer() throws SQLException, InterruptedException {
Thread thread = new Thread("JavaFX Init Thread") {
public void run() {
Application.launch(Main.class);
}
};
thread.setDaemon(true);
thread.start();
Thread.sleep(5000);
}
#Test
public void firstTest() {
TextField textFieldMock = mock(TextField.class);
DatePicker datePickerMock = mock(DatePicker.class);
TestClass objectUnderTest = new TestClass();
when(textFieldMock.getText()).thenReturn("5000");
when(datePickerMock.getValue()).thenReturn(LocalDate.of(1990,1,1));
//rest of code to test
}
}
Exception when I initialize thread in two classes
Exception in thread "JavaFX IncomeTest Init Thread" java.lang.RuntimeException: java.lang.UnsatisfiedLinkError: Native Library C:\Program Files\Java\jdk1.8.0_144\jre\bin\glass.dll already loaded in another classloader
at com.sun.javafx.tk.quantum.QuantumToolkit.startup(QuantumToolkit.java:267)
at com.sun.javafx.application.PlatformImpl.startup(PlatformImpl.java:211)
at com.sun.javafx.application.LauncherImpl.startToolkit(LauncherImpl.java:675)
at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:695)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.UnsatisfiedLinkError: Native Library C:\Program Files\Java\jdk1.8.0_144\jre\bin\glass.dll already loaded in another classloader
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1907)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1824)
at java.lang.Runtime.load0(Runtime.java:809)
at java.lang.System.load(System.java:1086)
at com.sun.glass.utils.NativeLibLoader.loadLibraryFullPath(NativeLibLoader.java:201)
at com.sun.glass.utils.NativeLibLoader.loadLibraryInternal(NativeLibLoader.java:94)
at com.sun.glass.utils.NativeLibLoader.loadLibrary(NativeLibLoader.java:39)
at com.sun.glass.ui.Application.loadNativeLibrary(Application.java:112)
at com.sun.glass.ui.Application.loadNativeLibrary(Application.java:120)
at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39)
at com.sun.glass.ui.win.WinApplication$1.run(WinApplication.java:118)
at com.sun.glass.ui.win.WinApplication$1.run(WinApplication.java:91)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.glass.ui.win.WinApplication.<clinit>(WinApplication.java:91)
at com.sun.glass.ui.win.WinPlatformFactory.createApplication(WinPlatformFactory.java:39)
at com.sun.glass.ui.win.WinPlatformFactory.createApplication(WinPlatformFactory.java:36)
at com.sun.glass.ui.Application.run(Application.java:146)
at com.sun.javafx.tk.quantum.QuantumToolkit.startup(QuantumToolkit.java:257)
... 5 more
Exception when Thread is initialized only in first class
java.lang.ExceptionInInitializerError
at sun.reflect.GeneratedSerializationConstructorAccessor12.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.objenesis.instantiator.sun.SunReflectionFactoryInstantiator.newInstance(SunReflectionFactoryInstantiator.java:45)
at org.objenesis.ObjenesisBase.newInstance(ObjenesisBase.java:73)
at org.mockito.internal.creation.instance.ObjenesisInstantiator.newInstance(ObjenesisInstantiator.java:14)
at org.powermock.api.mockito.repackaged.ClassImposterizer.createProxy(ClassImposterizer.java:149)
at org.powermock.api.mockito.repackaged.ClassImposterizer.imposterise(ClassImposterizer.java:64)
at org.powermock.api.mockito.internal.mockcreation.DefaultMockCreator.createMethodInvocationControl(DefaultMockCreator.java:121)
at org.powermock.api.mockito.internal.mockcreation.DefaultMockCreator.createMock(DefaultMockCreator.java:69)
at org.powermock.api.mockito.internal.mockcreation.DefaultMockCreator.mock(DefaultMockCreator.java:46)
at org.powermock.api.mockito.PowerMockito.mock(PowerMockito.java:141)
at
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:68)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:326)
at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:89)
at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:97)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:310)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:131)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.access$100(PowerMockJUnit47RunnerDelegateImpl.java:59)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner$TestExecutorStatement.evaluate(PowerMockJUnit47RunnerDelegateImpl.java:147)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.evaluateStatement(PowerMockJUnit47RunnerDelegateImpl.java:107)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTest(PowerMockJUnit47RunnerDelegateImpl.java:82)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:298)
at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:87)
at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:50)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:218)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:160)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:134)
at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:34)
at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:44)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:136)
at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:121)
at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:57)
at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:59)
at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:252)
at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:141)
at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:112)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.maven.surefire.util.ReflectionUtils.invokeMethodWithArray(ReflectionUtils.java:189)
at org.apache.maven.surefire.booter.ProviderFactory$ProviderProxy.invoke(ProviderFactory.java:165)
at org.apache.maven.surefire.booter.ProviderFactory.invokeProvider(ProviderFactory.java:85)
at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:115)
at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:75)
Caused by: java.lang.IllegalStateException: Toolkit not initialized
at com.sun.javafx.application.PlatformImpl.runLater(PlatformImpl.java:273)
at com.sun.javafx.application.PlatformImpl.runLater(PlatformImpl.java:268)
at com.sun.javafx.application.PlatformImpl.setPlatformUserAgentStylesheet(PlatformImpl.java:550)
at com.sun.javafx.application.PlatformImpl.setDefaultPlatformUserAgentStylesheet(PlatformImpl.java:512)
at javafx.scene.control.Control.<clinit>(Control.java:87)
... 50 more

Create a class MockApp extends Application and have a static method init(). In that method create a new single thread in which to invoke the JavaFX platform start (basically what you've done already) with an appropriate guard. The guard (a boolean flag) guarantees that the method gets called maximum once. The point is that the thread never terminates, thus allowing you to access the JavaFX platform during the lifetime of all your tests. The catch is you need to add something like:
#BeforeClass
public void init() {
MockApp.init();
}
for each test class where you use JavaFX since you don't know the order in which tests run.
The approach (with minor changes) can be seen in practice here.

Javafx - Exception in thread "main" java.lang.ExceptionInInitializerError [duplicate]

My application is Swing-based. I would like to introduce JavaFX and configure it to render a Scene on a secondary display.
I could use a JFrame to hold a JFXPanel which could hold a JFXPanel but I would like to achieve this with JavaFX API.
Subclassing com.sun.glass.ui.Application and using Application.launch(this) is not an option because the invoking thread would be blocked.
When instantiating a Stage from Swing EDT, the error I get is:
java.lang.IllegalStateException: Toolkit not initialized
Any pointers?
EDIT: Conclusions
Problem: Non-trivial Swing GUI application needs to run JavaFX components. Application's startup process initializes the GUI after starting up a dependent service layer.
Solutions
Subclass JavaFX Application class and run it in a separate thread e.g.:
public class JavaFXInitializer extends Application {
#Override
public void start(Stage stage) throws Exception {
// JavaFX should be initialized
someGlobalVar.setInitialized(true);
}
}
Sidenote: Because Application.launch() method takes a Class<? extends Application> as an argument, one has to use a global variable to signal JavaFX environment has been initialized.
Alternative approach: instantiate JFXPanel in Swing Event Dispatcher Thread:
final CountDownLatch latch = new CountDownLatch(1);
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new JFXPanel(); // initializes JavaFX environment
latch.countDown();
}
});
latch.await();
By using this approach the calling thread will wait until JavaFX environment is set up.
Pick any solution you see fit. I went with the second one because it doesn't need a global variable to signal the initialization of JavaFX environment and also doesn't waste a thread.

Found a solution. If I just create a JFXPanel from Swing EDT before invoking JavaFX Platform.runLater it works.
I don't know how reliable this solution is, I might choose JFXPanel and JFrame if turns out to be unstable.
public class BootJavaFX {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new JFXPanel(); // this will prepare JavaFX toolkit and environment
Platform.runLater(new Runnable() {
#Override
public void run() {
StageBuilder.create()
.scene(SceneBuilder.create()
.width(320)
.height(240)
.root(LabelBuilder.create()
.font(Font.font("Arial", 54))
.text("JavaFX")
.build())
.build())
.onCloseRequest(new EventHandler<WindowEvent>() {
#Override
public void handle(WindowEvent windowEvent) {
System.exit(0);
}
})
.build()
.show();
}
});
}
});
}
}

Since JavaFX 9, you can run JavaFX application without extending Application class, by calling Platform.startup():
Platform.startup(() ->
{
// This block will be executed on JavaFX Thread
});
This method starts the JavaFX runtime.

The only way to work with JavaFX is to subclass Application or use JFXPanel, exactly because they prepare env and toolkit.
Blocking thread can be solved by using new Thread(...).
Although I suggest to use JFXPanel if you are using JavaFX in the same VM as Swing/AWT, you can find more details here: Is it OK to use AWT with JavaFx?

I checked the source code and this is to initialize it
com.sun.javafx.application.PlatformImpl.startup(()->{});
and to exit it
com.sun.javafx.application.PlatformImpl.exit();

I used following when creating unittests for testing javaFX tableview updates
public class testingTableView {
#BeforeClass
public static void initToolkit() throws InterruptedException
{
final CountDownLatch latch = new CountDownLatch(1);
SwingUtilities.invokeLater(() -> {
new JFXPanel(); // initializes JavaFX environment
latch.countDown();
});
if (!latch.await(5L, TimeUnit.SECONDS))
throw new ExceptionInInitializerError();
}
#Test
public void updateTableView() throws Exception {
TableView<yourclassDefiningEntries> yourTable = new TableView<>();
.... do your testing stuff
}
}
even though this post is not test related, then it helped me to get my unittest to work
without the BeforeClass initToolkit, then the instantiation of TableView in the unittest would yield a message of missing toolkit

There's also way to initialize toolkit explicitly, by calling:
com.sun.javafx.application.PlatformImpl#startup(Runnable)
Little bit hacky, due to using *Impl, but is useful, if you don't want to use Application or JXFPanel for some reason.
re-posting myself from this post

private static Thread thread;
public static void main(String[] args) {
Main main = new Main();
startup(main);
thread = new Thread(main);
thread.start();
}
public static void startup(Runnable r) {
com.sun.javafx.application.PlatformImpl.startup(r);
}
#Override
public void run() {
SoundPlayer.play("BelievexBelieve.mp3");
}
This is my solution. The class is named Main and implements Runnable. Method startup(Runnable r) is the key.

Using Jack Lin’s answer, I found that it fired off the run() twice. With a few modifications that also made the answer more concise, I offer the following;
import com.sun.javafx.application.PlatformImpl;
public class MyFxTest implements Runnable {
public static void main(String[] args) {
MyFxTest main = new MyFxTest();
PlatformImpl.startup((Runnable) main);
}
#Override
public void run() {
// do your testing;
System.out.println("Here 'tis");
System.exit(0); // Optional
}
}

JavaFX software design

In a JavaFX application, javafx.application.Application must be subclassed, and the inherited launch() method, although it's public, must be called from within this derived class, otherwise an exception is thrown. The launch() method then uses reflection to instantiate the derived class, making it difficult to set values for the class members without losing them when launching. All that appears totally unusual to me, and I was wondering why starting a JavaFX application is so complicated, if that kind of software design (design pattern?) has a name, or if it's just bad design?
EDIT:
To be more specific, I want to use the observer pattern, so my java application gets notified when a document was loaded, like this:
public class MyDocumentLoader extends Application
{
private ChangeListener<Worker.State> changeListener;
public void setChangeListener(ChangeListener<Worker.State> changeListener)
{
this.changeListener = changeListener;
}
...
public void loadDocument(String url)
{
webEngine.getLoadWorker().stateProperty().addListener(changeListener);
webEngine.load(url);
}
...
}
I need the callback member in several methods, and ideally I can have more than one instances of the class that loads documents, so I can set different ChangeListeners for different URLs.

My guess is that this design was motivated by the (vast) number of Swing applications that were incorrectly written, with the "primary" JFrames being instantiated and shown on the wrong thread (i.e. not on the AWT event dispatch thread). My guess is that so many Swing applications were incorrectly written that they had to defensively code the framework against the incorrect usage, and that they wanted to avoid this scenario with JavaFX.
Forcing (well, almost forcing, there are hack-arounds) an FX Application to start this way makes it much harder to write an application incorrectly in a similar way. The launch method (and the equivalent Oracle JVM startup process if you have an Application subclass without a main method and a call to launch) does quite a bit of boilerplate work: it starts the FX toolkit, instantiates the Application subclass and calls its init() method, then on the FX Application Thread it instantiates the primary Stage and passes it to the Application subclass's start(...) method. This then ensures everything is running on the correct thread.
You should basically consider the start(...) method in a JavaFX application as the replacement for the main(...) method in a "traditional" Java application, with the understanding it is invoked on the FX Application Thread.
My recommendation is that the Application subclass should be as minimal as possible; it should just delegate to something else to actually create the UI, and then should just place it in the primary stage and show it. Include a main method that does nothing other than call launch(...) as a fallback for non-JavaFX-aware JVMs. You should only have one instance of one Application subclass present in any JVM. This way your Application subclass has no class members to set, and so the issues you describe simply don't arise.
If you use FXML, this is actually fairly natural: the start(...) method essentially just delegates to the FXML-controller pair to do the real work. If you don't use FXML, create a separate class to do the actual layout, etc, and delegate to it. See this related question which gets at the same kind of idea.
Note also that your statement
the inherited launch() method, although it's public, must be called
from within this derived class
is not entirely accurate, as there is an overloaded form of the launch(...) method in which you can specify the application subclass. So, if you really need, you can just create a stub for starting the FX toolkit:
public class FXStarter extends Application {
#Override
public void start(Stage primaryStage) {
// no-op
}
}
Now you can do:
public class MyRegularApplication {
public static void main(String[] args) {
// start FX toolkit:
new Thread(() -> Application.launch(FXStarter.class)).start();
// other stuff here...
}
}
Note that launch does not return until the FX toolkit shuts down, so it is imperative to put this call in another thread. This potentially creates race conditions, where you may try to do something needing the FX toolkit before launch(...) has actually initialized it, so you should probably guard against that:
public class FXStarter extends Application {
private static final CountDownLatch latch = new CountDownLatch(1);
public static void awaitFXToolkit() throws InterruptedException {
latch.await();
}
#Override
public void init() {
latch.countDown();
}
#Override
public void start(Stage primaryStage) {
// no-op
}
}
and then
public class MyRegularApplication {
public static void main(String[] args) throws InterruptedException {
// start FX toolkit:
new Thread(() -> Application.launch(FXStarter.class)).start();
FXStarter.awaitFXToolkit();
// other stuff here...
}
}
SSCCE (I just used inner classes for everything so this is convenient to run, but in real life these would be standalone classes):
import java.util.Random;
import java.util.concurrent.CountDownLatch;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
public class BackgroundProcessDrivenApp {
public static void main(String[] args) throws InterruptedException {
Platform.setImplicitExit(false);
new Thread(() -> Application.launch(FXStarter.class)).start();
FXStarter.awaitFXToolkit();
new MockProcessor().doStuff() ;
}
public static class FXStarter extends Application {
private static final CountDownLatch latch = new CountDownLatch(1);
#Override
public void init() {
latch.countDown();
}
public static void awaitFXToolkit() throws InterruptedException {
latch.await();
}
#Override
public void start(Stage primaryStage) { }
}
public static class MockProcessor {
private final int numEvents = 10 ;
public void doStuff() {
Random rng = new Random();
try {
for (int event = 1 ; event <= numEvents; event++) {
// just sleep to mimic waiting for background service...
Thread.sleep(rng.nextInt(5000) + 5000);
String message = "Event " + event + " occurred" ;
Platform.runLater(() -> new Messager(message).showMessageInNewWindow());
}
} catch (InterruptedException exc) {
Thread.currentThread().interrupt();
} finally {
Platform.setImplicitExit(true);
}
}
}
public static class Messager {
private final String message ;
public Messager(String message) {
this.message = message ;
}
public void showMessageInNewWindow() {
Stage stage = new Stage();
Label label = new Label(message);
Button button = new Button("OK");
button.setOnAction(e -> stage.hide());
VBox root = new VBox(10, label, button);
root.setAlignment(Pos.CENTER);
Scene scene = new Scene(root, 350, 120);
stage.setScene(scene);
stage.setAlwaysOnTop(true);
stage.show();
}
}
}

JavaFX supports a great number of deployment and packaging strategies, ref. https://docs.oracle.com/javase/8/docs/technotes/guides/deploy/toc.html, and having a standardized lifecycle entry- and exit-point simplifies supporting all these strategies.
If you are struggling to initialize your main application class, due to it being instanciated by the JavaFX launcher, your best option is to use the Application.init() and Application.stop() methods, as James_D points out.

NetBeans' HintsController and EventQueue

We are building an application based on the Netbeans Platform, and one part of it is an editor for a specific language we use.
We have the following class to highlight errors in the syntax:
class SyntaxErrorsHighlightingTask extends org.netbeans.modules.parsing.spi.ParserResultTask {
public SyntaxErrorsHighlightingTask () {
}
#Override
public void run (org.netbeans.modules.parsing.spi.Parser.Result result, org.netbeans.modules.parsing.spi.SchedulerEvent event) {
try {
final javax.swing.text.Document document = result.getSnapshot().getSource ().getDocument(false);
final List<ErrorDescription> errors = new ArrayList<ErrorDescription> ();
// finds errors on the document and add them to 'errors' list
}
/***
OFFENDING CODE GOES HERE
***/
} catch (javax.swing.text.BadLocationException ex1) {
org.openide.util.Exceptions.printStackTrace (ex1);
} catch (org.netbeans.modules.parsing.spi.ParseException ex1) {
Exceptions.printStackTrace (ex1);
}
}
#Override
public int getPriority () {
return 100;
}
#Override
public Class<? extends Scheduler> getSchedulerClass () {
return Scheduler.EDITOR_SENSITIVE_TASK_SCHEDULER;
}
#Override
public void cancel () {
}
}
The offending code, that throws an exception, is this:
org.netbeans.spi.editor.hints.HintsController.setErrors (document, "testsequence", errors);
Based on searching results, it was changed to the following:
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
System.err.println("is EDT? " + SwingUtilities.isEventDispatchThread());
HintsController.setErrors (document, "testsequence", errors);
}
});
The following is what happens when a syntax error is introduced in the editor:
is EDT? true
SEVERE [org.openide.util.RequestProcessor]: Error in RequestProcessor org.netbeans.spi.editor.hints.HintsController$1
java.lang.IllegalStateException: Must be run in EQ
at org.netbeans.editor.Annotations.addAnnotation(Annotations.java:195)
at org.netbeans.modules.editor.NbEditorDocument.addAnnotation(NbEditorDocument.java:251)
at org.openide.text.NbDocument.addAnnotation(NbDocument.java:504)
at org.netbeans.modules.editor.hints.AnnotationHolder$NbDocumentAttacher.attachAnnotation(AnnotationHolder.java:235)
at org.netbeans.modules.editor.hints.AnnotationHolder.attachAnnotation(AnnotationHolder.java:208)
at org.netbeans.modules.editor.hints.AnnotationHolder.updateAnnotationOnLine(AnnotationHolder.java:674)
at org.netbeans.modules.editor.hints.AnnotationHolder.setErrorDescriptionsImpl(AnnotationHolder.java:899)
at org.netbeans.modules.editor.hints.AnnotationHolder.access$1300(AnnotationHolder.java:113)
at org.netbeans.modules.editor.hints.AnnotationHolder$4.run(AnnotationHolder.java:812)
at org.netbeans.editor.BaseDocument.render(BaseDocument.java:1409)
at org.netbeans.modules.editor.hints.AnnotationHolder.setErrorDescriptions(AnnotationHolder.java:809)
at org.netbeans.modules.editor.hints.HintsControllerImpl.setErrorsImpl(HintsControllerImpl.java:111)
at org.netbeans.modules.editor.hints.HintsControllerImpl.setErrors(HintsControllerImpl.java:93)
at org.netbeans.spi.editor.hints.HintsController$1.run(HintsController.java:79)
at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1424)
at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1968)
Caused: org.openide.util.RequestProcessor$SlowItem: task failed due to
at org.openide.util.RequestProcessor.post(RequestProcessor.java:425)
at org.netbeans.spi.editor.hints.HintsController.setErrors(HintsController.java:77)
at com.#.#.#.editor.parser.SyntaxErrorsHighlightingTask$1.run(SyntaxErrorsHighlightingTask.java:74)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:641)
at java.awt.EventQueue.access$000(EventQueue.java:84)
at java.awt.EventQueue$1.run(EventQueue.java:602)
at java.awt.EventQueue$1.run(EventQueue.java:600)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:611)
at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:148)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
[catch] at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
What happens is, the call is to HintsController is being made in the EDT (EventDispatch Thread). However, Annotations.addAnnotation() is being run in another thread - sometimes in the "System clipboard synchronizer" thread, sometimes in the "Inactive RequestProcessor" thread. Since it checks if its being run on the EDT, it always throws an IllegalStateException.
I'm no expert in using the Netbeans Platform, and I'm pretty new to this specific application on the company - so I might be missing something really obvious. Google didn't help much. Anyone has any advice?

Turns out, it was not a problem with the code after all.
As pointed on the NetBeans-dev list:
HintsController.setErrors can be called from any thread - it uses its
own worker thread, and reschedules to AWT thread when necessary.
The requirement to invoke Annotations.addAnnotation in AWT thread has
been removed quite some time ago by:
http://hg.netbeans.org/main-silver/rev/db82e4e0fbcc
The same changeset also removed automatic rescheduling into AWT thread
in NbDocument.addAnnotation. So it seems that the build you are using
has the second part of the changeset, but not the first part (...)
After a careful review of maven's pom.xml files, I realized that the application was loading newer versions of the libs while the module was loading older versions, so it would run the wrong code. Related SO question about that here.

Maybe you should try to update your errors with a method like this one :
private void updateError(javax.swing.text.Document document, List<ErrorDescription> errors) {
if(javax.swing.SwingUtilities.isEventDispatchThread()) {
HintsController.setErrors (document, "testsequence", errors);
}
else {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
HintsController.setErrors (document, "testsequence", errors);
}
});
}
}