调用 JavaFX FileChooser 时抛出 NullPointerException
JavaFX FileChooser throws NullPointerException when called
我在 JavaFX 中打开 FileChooser 时遇到问题，因为当我调用 showOpenDialog(...) 方法时它会抛出错误，我搜索了类似的线程，例如我在下面发布的 link 但找不到让它工作。
当我调用 EmailSenderController 上的 addHtml() 方法将 html 文件文本添加到 html 编辑器时抛出错误。
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)
主要class
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Reader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.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.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$MouseHandler.access00(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$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$handleMouseEvent3(GlassViewEventHandler.java:432)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
... 49 more
Caused by: java.lang.NullPointerException
at emailsender.controllers.EmailSenderController.addHtml(EmailSenderController.java:77)
... 59 more
问题是执行addHtml方法的controller和你最初创建的controller不一样。当您加载 EmailSender 时，FXMLLoader 使用空构造函数创建一个新控制器。因此，不会调用设置属性的构造函数，最终得到空属性。
要获得正确的控制器，请使用加载程序的 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，您的 class 架构有点奇怪。你应该只有一个 Application class。控制器永远不应该是应用程序 class。它的工作是控制视图，而不是 运行 整个 window。作为建议，更改您的配置以加载如上所示的视图和控制器。控制器属性必须在加载视图后立即设置。
然后在您的 EmailSender start 方法中，只需加载您希望在方法结束前首先显示的视图。
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。然后您指示控制器加载视图（巧合的是它代表的视图）。在加载视图时，将创建一个控制器的新实例，其构造函数为空（因此为空值）。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。
我在 JavaFX 中打开 FileChooser 时遇到问题，因为当我调用 showOpenDialog(...) 方法时它会抛出错误，我搜索了类似的线程，例如我在下面发布的 link 但找不到让它工作。
当我调用 EmailSenderController 上的 addHtml() 方法将 html 文件文本添加到 html 编辑器时抛出错误。
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)
主要class
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Reader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.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.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$MouseHandler.access00(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$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$handleMouseEvent3(GlassViewEventHandler.java:432)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
... 49 more
Caused by: java.lang.NullPointerException
at emailsender.controllers.EmailSenderController.addHtml(EmailSenderController.java:77)
... 59 more
问题是执行addHtml方法的controller和你最初创建的controller不一样。当您加载 EmailSender 时，FXMLLoader 使用空构造函数创建一个新控制器。因此，不会调用设置属性的构造函数，最终得到空属性。
要获得正确的控制器，请使用加载程序的 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，您的 class 架构有点奇怪。你应该只有一个 Application class。控制器永远不应该是应用程序 class。它的工作是控制视图，而不是 运行 整个 window。作为建议，更改您的配置以加载如上所示的视图和控制器。控制器属性必须在加载视图后立即设置。
然后在您的 EmailSender start 方法中，只需加载您希望在方法结束前首先显示的视图。
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。然后您指示控制器加载视图（巧合的是它代表的视图）。在加载视图时，将创建一个控制器的新实例，其构造函数为空（因此为空值）。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。