我正在创建一个项目，其中包括在3个帐户之间发送电子邮件。因此，我有3个通过服务器进行通信的客户端。对于每个客户端，我打开一个FXML窗口，在其中关联一个线程。在Server.java中，我的目的是打开另一个FXML窗口，在其中显示服务器的动作，第二个目的是在客户端和服务器之间创建连接以启动线程。 当我尝试启动server.java时，它给了我这个错误：

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

public class Server extends Application{

   public void activate() throws IOException {
         //here I start threads and there is connection between client and server
   }

   public void start(Stage stage) throws IOException {
           Parent root = FXMLLoader.load(getclass().getResource("EmailClient.fxml"));
           Scene scene = new Scene(root);
           stage.setScene(scene);
           stage.show();
   }

   public static void main(String[] args) throws IOException {
       Server s = new Server();
       launch(args);
       s.activate();
   }
}

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:566)
    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:566)
    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$2(LauncherImpl.java:195)
    at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: java.lang.IllegalaccessError: class com.sun.javafx.fxml.FXMLLoaderHelper (in unnamed module @0x694fcbc2) cannot access class com.sun.javafx.util.Utils (in module javafx.graphics) because module javafx.graphics does not export com.sun.javafx.util to unnamed module @0x694fcbc2
    at com.sun.javafx.fxml.FXMLLoaderHelper.<clinit>(FXMLLoaderHelper.java:38)
    at javafx.fxml.FXMLLoader.<clinit>(FXMLLoader.java:2056)
    at sample.Server.start(Server.java:37)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$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$10(PlatformImpl.java:428)
    at java.base/java.security.accessController.doPrivileged(Native Method)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$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.Server