cascer1 cascer1 - 3 months ago 43
Java Question

lang.NullPointerException when reading resource file outside initialization method

I'm working on a program that uses a resource bundle for strings for easy translation. The structure is:

src/
└── main
├── java
| └── Main.java
└── resources
├── Main.fxml
├── strings.properties
├── strings_en.properties
└── strings_nl.properties


When I load the properties file in my
start
method (This is a JavaFX application) it works fine:

@Override
public void start(Stage primaryStage) throws java.io.IOException {
resources = ResourceBundle.getBundle("strings", new Locale("nl"));
Parent root = FXMLLoader.load(getClass().getClassLoader().getResource("main.fxml"), resources);
primaryStage.setTitle(resources.getString("title"));
primaryStage.setScene(new Scene(root, 1280, 1024));
primaryStage.show();
}


I can see this by the fact that the title of the window has the correct string, as set in the properties file. Then when I try to access the same
resources
variable elsewhere, I get a
lang.NullPointerException
:

@FXML
private void addItem(ActionEvent e) {
try {
...
} catch (NoResultException ex) {
Alert alert = new Alert(AlertType.ERROR);
alert.setTitle(resources.getString("err.unknownItem.title")); // Throws NullPointerException
alert.setHeaderText(resources.getString("err.unknownItem.header"));
alert.setContentText(resources.getString("err.unknownItem.text"));

alert.show();
}
}


I tried moving the code inside the
catch
-block to the
start
method, where it works fine.

The full stacktrace is

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8411)
at com.sun.javafx.scene.control.behavior.TextFieldBehavior.fire(TextFieldBehavior.java:179)
at com.sun.javafx.scene.control.behavior.TextInputControlBehavior.callAction(TextInputControlBehavior.java:178)
at com.sun.javafx.scene.control.behavior.BehaviorBase.callActionForEvent(BehaviorBase.java:218)
at com.sun.javafx.scene.control.behavior.TextInputControlBehavior.callActionForEvent(TextInputControlBehavior.java:127)
at com.sun.javafx.scene.control.behavior.BehaviorBase.lambda$new$74(BehaviorBase.java:135)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$KeyHandler.process(Scene.java:3964)
at javafx.scene.Scene$KeyHandler.access$1800(Scene.java:3910)
at javafx.scene.Scene.impl_processKeyEvent(Scene.java:2040)
at javafx.scene.Scene$ScenePeerListener.keyEvent(Scene.java:2501)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:216)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:148)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleKeyEvent$353(GlassViewEventHandler.java:247)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleKeyEvent(GlassViewEventHandler.java:246)
at com.sun.glass.ui.View.handleKeyEvent(View.java:546)
at com.sun.glass.ui.View.notifyKey(View.java:966)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
... 53 more
Caused by: java.lang.NullPointerException
at Main.addItem(Main.java:116)
... 63 more

Answer

I'm guessing from the comments below the question that you are using the same class for the Application class and for the controller class. Don't do this.. it causes mayhem.

Basically, the start() method is invoked on the instance of the Application subclass created by launch(). The event handler method is invoked on the instance of the controller class that is created by the FXMLLoader. If you use the same class for both (don't), then the resources field will be initialized in the instance created by launch(), but it won't be initialized in the instance created by the FXMLLoader (because it's a different object entirely).

Use a different class for the controller and the application.

Note that in a controller, you can define an initialize method which is automatically passed a reference to the resource bundle, so you can do:

public class Controller {

    private ResourceBundle resources ;

    public void initialize(URL location, ResourceBundle resources) {
        this.resources = resources ;
    }

    // ..
}

Also note that the following, while undocumented, also seems to work:

public class Controller {

    @FXML
    private ResourceBundle resources ;

    // ...

}

Here you must use the field name resources.