JavaFX FXML Application won't run

问题

I'm trying to follow the tutorial here. But, my IDE, Eclipse, doesn't seem to want to work with it. I've tried copying and pasting the code examples into my IDE, but the same error pops up. Unfortunately, no window is displayed.

Please help me figure out what's wrong with this code.

The error:

 Exception in Application start method
    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 com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
        at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
        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.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
    Caused by: java.lang.RuntimeException: Exception in Application start method
        at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
        at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$154(LauncherImpl.java:182)
        at java.lang.Thread.run(Thread.java:748)
    Caused by: java.lang.NullPointerException: Location is required.
        at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3207)
        at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3175)
        at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3148)
        at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3124)
        at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3104)
        at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3097)
        at application.RegistrationFormApplication.start(RegistrationFormApplication.java:13)
        at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$161(LauncherImpl.java:863)
        at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$174(PlatformImpl.java:326)
        at com.sun.javafx.application.PlatformImpl.lambda$null$172(PlatformImpl.java:295)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.javafx.application.PlatformImpl.lambda$runLater$173(PlatformImpl.java:294)
        at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
        at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
        at com.sun.glass.ui.gtk.GtkApplication.lambda$null$48(GtkApplication.java:139)
        ... 1 more
    Exception running application application.RegistrationFormApplication

main class:

package application;

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

public class RegistrationFormApplication extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("registration_form.fxml"));
        primaryStage.setTitle("Registration Form FXML Application");
        primaryStage.setScene(new Scene(root, 800, 500));
        primaryStage.show();
    }


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

FXML document:

<?import javafx.scene.layout.GridPane?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.text.Font?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.control.PasswordField?>
<?import javafx.scene.control.Button?>

<GridPane fx:controller="javafx.example.RegistrationFormController"
          xmlns:fx="http://javafx.com/fxml" alignment="center"
          hgap="10" vgap="10">
    <padding><Insets top="40" right="40" bottom="40" left="40"/></padding>
    <columnConstraints>
        <ColumnConstraints minWidth="100" prefWidth="100"
                           maxWidth="Infinity" halignment="RIGHT">
        </ColumnConstraints>
        <ColumnConstraints minWidth="200" prefWidth="200"
                           maxWidth="Infinity" hgrow="ALWAYS">
        </ColumnConstraints>
    </columnConstraints>

    <!-- Add Header Label -->
    <Label text="Registration Form (FXML)" GridPane.columnIndex="0" 
           GridPane.rowIndex="0" GridPane.columnSpan="2" 
           GridPane.rowSpan="1" GridPane.halignment="CENTER" >
        <font>
            <Font name="Arial" size="24" ></Font>
        </font>
        <GridPane.margin>
            <Insets top="20" right="0" bottom="20" left="0"></Insets>
        </GridPane.margin>
    </Label>



    <!-- Add Name Label -->
    <Label text="Full Name : " GridPane.columnIndex="0" 
           GridPane.rowIndex="1" >
    </Label>
    <!-- Add Name Text Field -->
    <TextField fx:id="nameField" prefHeight="40" 
               GridPane.columnIndex="1" GridPane.rowIndex="1"/>


    <!-- Add Email Label -->
    <Label text="Email ID : " GridPane.columnIndex="0" 
           GridPane.rowIndex="2" >
    </Label>
    <!-- Add Email Text Field -->
    <TextField fx:id="emailField" prefHeight="40" 
               GridPane.columnIndex="1" GridPane.rowIndex="2"/>



    <!-- Add Password Label -->
    <Label text="Password : " GridPane.columnIndex="0" 
           GridPane.rowIndex="3" >
    </Label>
    <!-- Add Password Field -->
    <PasswordField fx:id="passwordField" prefHeight="40" 
                   GridPane.columnIndex="1" GridPane.rowIndex="3"/>


    <!-- Add Submit Button -->
    <Button fx:id="submitButton" text="Submit"
            prefWidth="100" prefHeight="40" defaultButton="true"
            GridPane.columnIndex="0" GridPane.rowIndex="4"
            GridPane.columnSpan="2" GridPane.rowSpan="1"
            GridPane.halignment="CENTER"
            onAction="#handleSubmitButtonAction">
        <GridPane.margin>
            <Insets top="20" right="0" bottom="20" left="0"></Insets>
        </GridPane.margin>
    </Button>
</GridPane>

Class that uses the FXML document:

package application;

import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.Alert;
import javafx.scene.control.Button;
import javafx.scene.control.PasswordField;
import javafx.scene.control.TextField;
import javafx.stage.Window;

public class RegistrationFormController {
    @FXML
    private TextField nameField;

    @FXML
    private TextField emailField;

    @FXML
    private PasswordField passwordField;

    @FXML
    private Button submitButton;

    @FXML
    protected void handleSubmitButtonAction(ActionEvent event) {
        Window owner = submitButton.getScene().getWindow();
        if(nameField.getText().isEmpty()) {
            AlertHelper.showAlert(Alert.AlertType.ERROR, owner, "Form Error!", 
                    "Please enter your name");
            return;
        }
        if(emailField.getText().isEmpty()) {
            AlertHelper.showAlert(Alert.AlertType.ERROR, owner, "Form Error!", 
                    "Please enter your email id");
            return;
        }
        if(passwordField.getText().isEmpty()) {
            AlertHelper.showAlert(Alert.AlertType.ERROR, owner, "Form Error!", 
                    "Please enter a password");
            return;
        }

        AlertHelper.showAlert(Alert.AlertType.CONFIRMATION, owner, "Registration Successful!", 
                "Welcome " + nameField.getText());
    }
}

AlertHelper class (called in above class):

package application;

import javafx.scene.control.Alert;
import javafx.stage.Window;

public class AlertHelper {

    public static void showAlert(Alert.AlertType alertType, Window owner, String title, String message) {
        Alert alert = new Alert(alertType);
        alert.setTitle(title);
        alert.setHeaderText(null);
        alert.setContentText(message);
        alert.initOwner(owner);
        alert.show();
    }
}

回答1:

I had two issues that caused the program to fail to display correctly.

First, the line

Parent root = FXMLLoader.load(getClass().getResource("registration_form.fxml"));

should've been,

Parent root = FXMLLoader.load(getClass().getResource("/registration_form.fxml"));

Also, my graphics drivers were out of date.

Since my operating system is Ubuntu 18.04 the process to update them was as follows.

First, I opened the program "Ubuntu Software", clicked "Software & Updates" in the upper-right hand side of the screen, and clicked the tab, "Additional Drivers" on the window that popped up.

Then, I selected "NVIDIA driver metapackage from nvidia-driver-410" and clicked "Apply Changes".

This solved my issue, and allowed the program to display properly.

来源：https://stackoverflow.com/questions/52797309/javafx-fxml-application-wont-run