Why Parent root =FXMLLoader is not working properly?

问题

I am trying to build an app in JavaFX but i am facing the issue. Below code generating error.I error are showing since i created the project. I downloaded the JavaFX 14 from "https://gluonhq.com/products/javafx/" and include all jar files present in lib directory.


import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setTitle("Hello World");
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }


    public static void main(String[] args) {
        launch(args);
    }
}

But This code works fine

package sample;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        //Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        StackPane root=new StackPane();
        primaryStage.setTitle("Hello World");
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }


    public static void main(String[] args) {
        launch(args);
    }
}

Getting this error:

"C:\Program Files\Java\jdk-14.0.1\bin\java.exe" --add-modules javafx.base,javafx.graphics --add-reads javafx.base=ALL-UNNAMED --add-reads javafx.graphics=ALL-UNNAMED "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2020.1.3\lib\idea_rt.jar=60984:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2020.1.3\bin" -Dfile.encoding=UTF-8 -classpath E:\Shapes\out\production\Shapes;E:\Software\javafx-sdk-14.0.2.1\lib\javafx-swt.jar;E:\Software\javafx-sdk-14.0.2.1\lib\javafx.base.jar;E:\Software\javafx-sdk-14.0.2.1\lib\javafx.controls.jar;E:\Software\javafx-sdk-14.0.2.1\lib\javafx.fxml.jar;E:\Software\javafx-sdk-14.0.2.1\lib\javafx.graphics.jar;E:\Software\javafx-sdk-14.0.2.1\lib\javafx.media.jar;E:\Software\javafx-sdk-14.0.2.1\lib\javafx.swing.jar;E:\Software\javafx-sdk-14.0.2.1\lib\javafx.web.jar -p E:\Software\javafx-sdk-14.0.2.1\lib\javafx.base.jar;E:\Software\javafx-sdk-14.0.2.1\lib\javafx.graphics.jar sample.Main
Exception in Application start method
java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:464)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:900)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:195)
    at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: java.lang.IllegalAccessError: class com.sun.javafx.fxml.FXMLLoaderHelper (in unnamed module @0x66dac2b5) cannot access class com.sun.javafx.util.Utils (in module javafx.graphics) because module javafx.graphics does not export com.sun.javafx.util to unnamed module @0x66dac2b5
    at com.sun.javafx.fxml.FXMLLoaderHelper.<clinit>(FXMLLoaderHelper.java:38)
    at javafx.fxml.FXMLLoader.<clinit>(FXMLLoader.java:2056)
    at sample.Main.start(Main.java:14)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(LauncherImpl.java:846)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$12(PlatformImpl.java:455)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:428)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:427)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
    ... 1 more
Exception running application sample.Main

Process finished with exit code 1

回答1:

The fundamental error is (formatted for readability):

Caused by: java.lang.IllegalAccessError: 
    class com.sun.javafx.fxml.FXMLLoaderHelper (in unnamed module @0x66dac2b5) 
    cannot access class com.sun.javafx.util.Utils (in module javafx.graphics) 
    because module javafx.graphics does not export com.sun.javafx.util to unnamed module @0x66dac2b5

That error is telling you that the javafx.fxml module has ended up on the class-path while the javafx.graphics module is on the module-path. This scenario prevents the special access to internal code the javafx.graphics module grants to the javafx.fxml module.

The solution to this is to do one of the following:

Include javafx.fxml in your --add-modules VM argument.
Make your own code modular, add the necessary requires, exports, and opens directives, and launch your application with --module.

If you're curious about how the above error comes about then my answer to another question goes into more detail. Note it focuses on the javafx.media module but the concept is the same.

来源：https://stackoverflow.com/questions/63301170/why-parent-root-fxmlloader-is-not-working-properly

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