JavaFX：线程“ JavaFX Application Thread”中的异常java.lang.RuntimeException：java.lang.reflect.InvocationTargetException提出问题

Question

我正在尝试创建一个简单的程序来在2个字段中接受用户输入，然后将其保存为字符串并将其写入文件。

出现无法识别的错误，无法在任何地方找到问题，希望有人可以向我解释。

我的控制器.Java

        import java.io.*;
        import javafx.event.ActionEvent;
        import javafx.fxml.FXML;
        import javafx.scene.control.Button;
        import javafx.scene.control.TextField;


public class Controller {


    @FXML
    private TextField InputEmail;

    @FXML
    private TextField InputName;

    //Output writer String
    public String Output;


    public void handleButtonAction(ActionEvent event) {
        Output = "Student Name: " + InputName.getText() + "|| Student Email: " + InputEmail.getText() + "\n";
    }

    public void Add(ActionEvent event) {
        try {
            FileWriter fw = new FileWriter("D:/Assignment3&4_Output.txt");
            fw.write(Output);
            System.out.println("File updated");
        } catch (IOException e) {
            System.out.println("File could not be found. Please check the file path.");


        }
    }
}

我的sample.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import java.lang.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.text.*?>

<GridPane alignment="center" hgap="10" vgap="10" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
      <SplitPane dividerPositions="0.25252525252525254, 0.5252525252525253" orientation="VERTICAL" prefHeight="200.0" prefWidth="160.0">
        <items>
          <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="100.0" prefWidth="160.0">
               <children>
                  <Label layoutX="12.0" layoutY="12.0" text="Create Student" textFill="#32d9ff">
                     <font>
                        <Font name="Arial" size="20.0" />
                     </font>
                  </Label>
               </children>
            </AnchorPane>
          <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="100.0" prefWidth="160.0">
               <children>
                  <TextField id="InputName" fx:id="InputName" layoutX="5.0" layoutY="13.0" onInputMethodTextChanged="#handleButtonAction" promptText="Student Firstname" />
               </children>
            </AnchorPane>
            <AnchorPane layoutX="10.0" layoutY="10.0" minHeight="0.0" minWidth="0.0" prefHeight="68.0" prefWidth="158.0">
               <children>
                  <TextField id="InputEmail" fx:id="InputEmail" layoutX="5.0" layoutY="14.0" onAction="#handleButtonAction" promptText="Student Email" />
                  <Button id = "button" fx:id="button" layoutX="60.0" layoutY="46.0" mnemonicParsing="false" text="Add" onAction="#Add" />
               </children>
            </AnchorPane>
        </items>
      </SplitPane>
   </children>
   <columnConstraints>
      <ColumnConstraints />
   </columnConstraints>
   <rowConstraints>
      <RowConstraints />
   </rowConstraints>
</GridPane>

我的Main.Java

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 Main extends Application {

    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setTitle("Hello World");
        primaryStage.setScene(new Scene(root, 300, 275));
        primaryStage.show();
    }


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

最后是当我尝试使用“添加”按钮并编写表格时抛出的错误。

    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1787)
    at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1670)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8879)
    at javafx.controls/javafx.scene.control.Button.fire(Button.java:200)
    at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:206)
    at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3851)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.access$1200(Scene.java:3579)
    at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
    at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2588)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:397)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:434)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:390)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:433)
    at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
    at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
    at java.base/java.lang.Thread.run(Thread.java:835)
Caused by: java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
    at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:273)
    at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1782)
    ... 51 more
Caused by: java.lang.NullPointerException
    at java.base/java.io.Writer.write(Writer.java:249)
    at sample.Controller.Add(Controller.java:29)
    ... 62 more

由于我是Java的新手，所以非常感谢任何帮助。

Answer 1

[从外观上看，您的程序从不设置Output的值（在方法顶部用System.out.println(Output)确认），也许根本就没有Output的字符串，您只是把handleButtonAction方法中的所有逻辑都放在了在像这样添加

public void Add(ActionEvent event) {
        try {
            FileWriter fw = new FileWriter("D:/Assignment3&4_Output.txt");
            fw.append("Student Name: " + InputName.getText() + "|| Student Email: " + InputEmail.getText() + "\n");
            fw.close();
            System.out.println("File updated");
        } catch (IOException e) {
            System.out.println("File could not be found. Please check the file path.");


        }
    }

或将输出字符串分配移至add()

public void Add(ActionEvent event) {
    output ="Student Name: " + InputName.getText() + "|| Student Email: " + 
    InputEmail.getText() + "\n"
        try {
            FileWriter fw = new FileWriter("D:/Assignment3&4_Output.txt");
            fw.append(output);
            fw.close();
            System.out.println("File updated");
        } catch (IOException e) {
            System.out.println("File could not be found. Please check the file path.");


        }
    }

append(String s)方法添加而不是覆盖，您可以使用此方法为可选close()方法将流刷新到文件中（保存文件）并关闭流。

P.S。 You should make the first letter of everything except classes lowercase