JavaFX FileChooser 调用时抛出 NullPointerException答案

【问题标题】：JavaFX FileChooser throws NullPointerException when calledJavaFX FileChooser 调用时抛出 NullPointerException
【发布时间】：2018-08-13 14:18:25
【问题描述】：

我在 JavaFX 中打开 FileChooser 时遇到问题，因为当我调用 showOpenDialog(...) 方法时它会引发错误，我搜索了类似的线程，例如我在下面发布的链接，但无法使其工作。

当我在 EmailSenderController 上调用 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，但我没有像他那样初始化@FXML 注入控件：JavaFX FileChooser Throws Error (probably easy fix, but still confused)

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);
        }

    }

查看加载器服务

    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);
    }

}

控制器

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();
    }

}

文件阅读器服务

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;
    }

}

错误

    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

【问题讨论】：

你能在addHtml方法中测试fileReaderService属性不为空吗？我怀疑控制器的构造方式可能是罪魁祸首。一个简单的if(fileReaderService==null){System.out.println("fileReaderService is null");} 就可以了
@TM00 确实为空，但我需要调用它，因为该方法会打开文件选择器，有点奇怪 fileReaderService 为空。
FXMLLoader 如果存在fx:controller 属性，则使用不带参数的构造函数来创建控制器实例。可能这就是发生的事情，fileReaderService 为空......看看这个问题，了解正确传递参数的方法：stackoverflow.com/questions/14187963/…
那么问题不在于 FileChooser。您的问题在于您创建控制器的方式。加载fxml文件的时候有没有使用FXMLLoader的getController方法设置属性？如果没有，请添加显示您如何加载视图的代码。
@fabian 但另一个 ViewLoaderService 工作正常，你所说的意思是传递给控制器的两个类都不应该工作，但其中一个可以工作。

标签： javafx filechooser

【解决方案1】：

问题是执行addHtml方法的控制器和你最初创建的那个不一样。当您加载 EmailSender 时，FXMLLoader 使用空构造函数来创建一个新控制器。因此，不会调用设置属性的构造函数，并且您最终会得到空属性。

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

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

另一方面，你的类架构有点奇怪。你应该只有一个Application 类。控制器永远不应该是应用程序类。它的工作是控制视图，而不是运行整个窗口。作为建议，更改您的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。

然后在您的EmailSenderstart 方法中，只需在方法结束之前加载您想要首先显示的视图。

编辑

您的 ViewLoaderService 当前工作的原因是您设置程序的方式，并说明了为什么控制器不应该是应用程序。您创建具有属性的控制器实例。然后你指示控制器加载视图（巧合的是它所代表的视图）。在加载视图时，将使用其空构造函数（因此为空值）创建控制器的新实例。然后这个新控制器充当显示视图的控制器，而不是您在应用程序开始时创建的控制器。

【讨论】：

所以最后：我在 EmailSender 中创建了一个实例，FXMLLoader 创建了另一个实例，我尝试将 2 个引用传递给从未调用过的构造函数，因此我需要将它们传递给使用创建的控制器 FXMLLoader loader.getController() 获取引用，然后使用 setter 和 getter 传递服务。无论如何，我会根据你所说的改变架构。
正确 :) 如果您对答案感到满意，您应该考虑接受它。