JavaFX项目中应用程序构造函数中的异常

Question

我将我的旧JavaFX项目迁移到JavaFX。为此，我使用openjdk-17。启动此代码时，将捕获应用程序构造函数中的异常。也许我用了不对的词？但是为什么编译器在构建我的项目时会说好呢？

我的堆栈追踪

Exception in Application constructor
Exception in thread "main" java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1071)
Caused by: java.lang.RuntimeException: Unable to construct Application instance: class classes.Main
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:891)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:196)
    at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.lang.IllegalAccessException: class com.sun.javafx.application.LauncherImpl (in module javafx.graphics) cannot access class classes.Main (in module com.example.javacoursework) because module com.example.javacoursework does not export classes to module javafx.graphics
    at java.base/jdk.internal.reflect.Reflection.newIllegalAccessException(Reflection.java:392)
    at java.base/java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:674)
    at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:489)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$8(LauncherImpl.java:803)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$12(PlatformImpl.java:484)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:457)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:456)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run$$$capture(InvokeLaterDispatcher.java:96)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
    ... 1 more

我的代码

package classes;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.*;
import javafx.scene.control.Button;
import javafx.stage.Stage;

import java.io.IOException;
import java.net.URL;
import java.util.Objects;

public class Main extends Application //Error occured in constructor!?
{
    @Override
    public void start(Stage primaryStage) throws IOException
    {
        Button button = new Button("Hello");
        Scene scene = new Scene(button);
        primaryStage.setScene(scene);
        primaryStage.show();
//        Parent root = FXMLLoader.load(Objects.requireNonNull(getClass().getResource("../../resources/123.fxml")));
//        primaryStage.setTitle("Vote app");
//        primaryStage.setScene(new Scene(root));
//        primaryStage.setResizable(false);
//        primaryStage.show();
    }

    public static void main(String[] args)
    {
        //launch(args);
        System.out.println("Hello World!");
    }
}

如果需要更多的信息，我会添加到这个帖子。

Answer 1

JavaFX框架使用反射实例化您的Application实现类。如果所述模块提供了必要的“权限”，则代码只能反射地访问单独模块中的代码。如果没有授予这些“权限”，则将引发IllegalAccessException。

这里是您的根本例外：

Caused by: java.lang.IllegalAccessException: class com.sun.javafx.application.LauncherImpl (in module javafx.graphics) cannot access class classes.Main (in module com.example.javacoursework) because module com.example.javacoursework does not export classes to module javafx.graphics

解决办法很简单。只需向模块信息描述符(module-info.java)添加以下指令：

exports classes to javafx.graphics;

需要导出的包以及需要导出的模块可以通过读取异常消息来确定。注意，您只需要使用exports而不是opens，因为JavaFX应用程序类及其构造函数必须是public。

它可能有助于阅读：What is a stack trace, and how can I use it to debug my application errors?

Answer 2

问题不在您的代码中。这是你的项目/启动设置。到这里来看看如何正确配置Maven。https://openjfx.io/openjfx-docs/