JavaFX FileChooser在调用时引发NullPointerException

Question

当我调用EmailSenderController上的addHtml（）方法将html文件文本添加到html编辑器时，会引发错误。

类似的线程，但例外是我没有像他那样初始化@fxml inject控件：JavaFX FileChooser抛出错误（可能很容易修复，但仍然混乱）

主类

package emailsender;

import configuration.ProjectConfiguration;
import emailsender.controllers.EmailSenderController;
import emailsender.services.FileReaderService;
import emailsender.services.ViewLoaderService;
import java.io.IOException;
import javafx.application.Application;
import javafx.stage.Stage;

/**
 *
 * @author DJava
 */
public class EmailSender extends Application {

    @Override
    public void start(Stage primaryStage) throws IOException, Exception 
    {

        //Main configuration
        ProjectConfiguration configuration = new 
        ProjectConfiguration();
        configuration.setStage(primaryStage);
        configuration.setViewsPath("emailsender/views/");

        //Services
        ViewLoaderService viewloaderService = new 
        ViewLoaderService(configuration);
        FileReaderService fileReaderService = new 
        FileReaderService(configuration);

        //Controllers
        EmailSenderController sender = new 
        EmailSenderController(viewloaderService, fileReaderService);
        sender.start(configuration.getStage());
        }

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

    }

    package emailsender.services;

import configuration.ProjectConfiguration;
import java.io.IOException;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;

/**
 *
 * @DJava
 */
public class ViewLoaderService {

    ProjectConfiguration configuration;

    public ViewLoaderService(ProjectConfiguration configuration) {

        this.configuration = configuration;
    }

    public Scene loadViewOnScene(String view) throws IOException {

        Parent root = FXMLLoader.load(getClass().getClassLoader().getResource(this.configuration.getViewsPath() + view + ".fxml"));
        return new Scene(root);
    }

}

package emailsender.controllers;

import emailsender.services.FileReaderService;
import javafx.application.Application;
import javafx.stage.Stage;
import emailsender.services.ViewLoaderService;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.control.MenuItem;
import javafx.scene.control.ProgressIndicator;
import javafx.scene.control.TextField;
import javafx.scene.web.HTMLEditor;
import javafx.scene.web.WebEngine;
import javafx.scene.web.WebView;

/**
 *
 * @author DJava
 */
public class EmailSenderController extends Application {

    private ViewLoaderService viewLoaderService;
    private FileReaderService fileReaderService;
    private WebEngine webEngine;

    //Header
    //EmaiLSender menu
    @FXML
    public MenuItem newListMenuItem;
    @FXML
    public MenuItem preferencesMenuItem;
    @FXML
    public MenuItem closeMenuItem;

    //Help menu
    @FXML
    public MenuItem aboutMenuItem;

    //Email tab
    @FXML
    public TextField subjectTextField;
    @FXML
    public ComboBox destinationListComboBox;
    @FXML
    public Button addHtmlButton;
    @FXML
    public HTMLEditor messageEditor;
    @FXML
    public ProgressIndicator sendTaskProgressIndicator;

    //Preview tab
    @FXML
    public WebView previewWebView;

    //Footer
    @FXML
    public Button sendButton;

    public EmailSenderController() {
    }

    public EmailSenderController(ViewLoaderService viewLoaderService, 
    FileReaderService fileReaderService) {

        this.viewLoaderService = viewLoaderService;
        this.fileReaderService = fileReaderService;
    }

    @FXML
    public void addHtml() {

    this.messageEditor.setHtmlText
    (this.fileReaderService.getFileText()); // Here is the problem ..........
    }

    @FXML
    public void previewEmail() {

        this.webEngine = this.previewWebView.getEngine();
        this.webEngine.loadContent(this.messageEditor.getHtmlText());
    }

    @FXML
    public void sendEmail() {

        this.sendTaskProgressIndicator.setProgress(0.3D);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {

        primaryStage.setTitle("EmailSender");
        primaryStage.setScene(viewLoaderService.loadViewOnScene("EmailSender"));
        primaryStage.setResizable(false);
        primaryStage.show();
    }

}

package emailsender.services;

import configuration.ProjectConfiguration;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import javafx.stage.FileChooser;

/**
 *
 * @author DJava
 */
public class FileReaderService {

    private final ProjectConfiguration configuration;
    private final FileChooser fileChooser;

    public FileReaderService(ProjectConfiguration configuration) {

        this.configuration = configuration;
        this.fileChooser = new FileChooser();
    }

    public String getFileText() {

        String text = "";

        try {

            BufferedReader reader = new BufferedReader(new FileReader(this.fileChooser.showOpenDialog(this.configuration.getStage())));
            String line;
            while ((line = reader.readLine()) != null) {

                text += line + "\n";
            }

        } catch (IOException event) {
            event.printStackTrace();
        }
        System.out.println(text);
        return text;
    }

}

    Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Node.fireEvent(Node.java:8413)
    at javafx.scene.control.Button.fire(Button.java:185)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:394)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$353(GlassViewEventHandler.java:432)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
    ... 49 more
Caused by: java.lang.NullPointerException
    at emailsender.controllers.EmailSenderController.addHtml(EmailSenderController.java:77)
    ... 59 more

Answer 1

问题是执行addhtml方法的控制器与最初创建的控制器不同。加载电子邮件发送器时，FXMLLoader使用空构造函数创建新控制器。因此，设置属性的构造函数不会被调用，最终会得到null属性。

要获得正确的控制器，请使用加载器的getController方法，并使用适当的set方法设置属性：

FXMLLoader loader = new FXMLLoader("fxml file") ;
loader.load();
EmailSenderController controller = (EmailSenderController)  loader .getController() ;
controller.setFileReadService(frs) ; // frs created elsewhere

另外，您的类架构有点奇怪。您应该只有一个application类。控制器永远不应该是应用程序类。它的工作是控制一个视图，而不是运行整个窗口。建议您更改配置以加载视图和控制器，如上所示。控制器属性必须在加载视图后立即设置。