Question

你好，我是Java语言的新手。我不断收到此错误

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.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:8411)
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.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$2(GlassViewEventHandler.java:432)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:410)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$3(WinApplication.java:177)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
... 48 more
Caused by: java.io.FileNotFoundException: Test.txt (The system cannot find the file specified)
at java.io.FileInputStream.open0(Native Method)
at java.io.FileInputStream.open(FileInputStream.java:195)
at java.io.FileInputStream.<init>(FileInputStream.java:138)
at java.io.FileInputStream.<init>(FileInputStream.java:93)
at java.io.FileReader.<init>(FileReader.java:58)
at cw3.Controller.loadPressed(Controller.java:48)

所以我想做的是使Java读取文本文件，然后使用内部信息计算均值。这是我的代码main.java

package cw3;

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

public class Main extends Application{

@Override
public void start(Stage primaryStage) throws Exception{
    Parent root = FXMLLoader.load(getClass().getResource("Calc.fxml"));
    primaryStage.setTitle("TEST");
    primaryStage.setScene(new Scene(root));
    primaryStage.show();
}

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

Controller.java

package cw3;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.TextArea;

//To open the load window
import javafx.stage.FileChooser;
import javafx.stage.Stage;

public class Controller {

@FXML // ResourceBundle that was given to the FXMLLoader
private ResourceBundle resources;

@FXML // URL location of the FXML file that was given to the FXMLLoader
private URL location;

@FXML // fx:id="load"
private Button load; // Value injected by FXMLLoader

@FXML // fx:id="mean"
private TextArea mean; // Value injected by FXMLLoader

@FXML
void loadPressed(ActionEvent event) throws FileNotFoundException, IOException{

 FileChooser myfileChooser = new FileChooser();
 myfileChooser.setTitle("Open..."); 
 File FileDestination = myfileChooser.showOpenDialog(new Stage());
 String filename = FileDestination.getName();

 System.out.print(filename);

 // FileReader reads text files in the default encoding.
 FileReader fileReader = new FileReader(filename);

 // Always wrap FileReader in BufferedReader.
 BufferedReader bufferedReader = new BufferedReader(fileReader);
 String inputFileLine = null;
 double Mean = 0;
 int totalnumber = 0;


 while ((inputFileLine = bufferedReader.readLine()) != null) {
     Mean += Double.valueOf(inputFileLine);
     totalnumber++;
 }
 double showmean = Mean/totalnumber;
 mean.setText(String.valueOf(showmean));
}

@FXML // This method is called by the FXMLLoader when initialization is complete
void initialize() {
    assert load != null : "fx:id=\"load\" was not injected: check your FXML file 'Calc.fxml'.";
    assert mean != null : "fx:id=\"mean\" was not injected: check your FXML file 'Calc.fxml'.";

}
}

请帮助我解决此错误，这有点令人困惑。在加载窗口中点击打开按钮后，我收到此错误。

P.S。我使用scenebuilder应用程序和netbean来开发Java应用程序。如果您想让我知道fxml文件，我相信fxml文件并不重要。

Answer 1

根本错误是：

Caused by: java.io.FileNotFoundException: Test.txt (The system cannot find the file specified)
        at java.io.FileInputStream.open0(Native Method)
        at java.io.FileInputStream.open(FileInputStream.java:195)
        at java.io.FileInputStream.<init>(FileInputStream.java:138)
        at java.io.FileInputStream.<init>(FileInputStream.java:93)
        at java.io.FileReader.<init>(FileReader.java:58)
        at cw3.Controller.loadPressed(Controller.java:48)

这是说文件Test.txt不存在，并且错误正在您的48类的行cw3.Controller上抛出。请查看What is a stack trace, and how can I use it to debug my application errors?问答以获取有关堆栈跟踪以及如何读取它们的更多信息。

在您的代码中：

@FXML
void loadPressed(ActionEvent event) throws FileNotFoundException, IOException{

 FileChooser myfileChooser = new FileChooser();
 myfileChooser.setTitle("Open..."); 
 File FileDestination = myfileChooser.showOpenDialog(new Stage());
 String filename = FileDestination.getName();

 System.out.print(filename);

 // FileReader reads text files in the default encoding.
 FileReader fileReader = new FileReader(filename);

 // Always wrap FileReader in BufferedReader.
 BufferedReader bufferedReader = new BufferedReader(fileReader);
 String inputFileLine = null;
 double Mean = 0;
 int totalnumber = 0;


 while ((inputFileLine = bufferedReader.readLine()) != null) {
     Mean += Double.valueOf(inputFileLine);
     totalnumber++;
 }
 double showmean = Mean/totalnumber;
 mean.setText(String.valueOf(showmean));
}

您正在将FileDestination.getName()的结果（顺便说一下，根据Java的命名约定，变量名以小写字母开头）传递给FileReader构造函数。 File#getName()的文档内容如下：

返回此抽象路径名表示的文件或目录的名称。 这只是路径名名称序列中的姓氏（添加了重点）。如果路径名的名称序列为空，则返回空字符串。

您需要通过完整路径。您可以通过File#getPath()执行此操作，但仅使用FileReader#<init>(File)构造函数并直接传递File对象可能会更容易。您还需要记住在完成操作后关闭FileReader；最简单的方法是使用try-with-resources statement。例如：

File chosenFile = ...;
try (BufferedReader br = new BufferedReader(new FileReader(chosenFile)) {
    // read from the BufferedReader
}
// Note: Closing the BufferedReader will close the nested FileReader

其他一些注意事项：

您可以使用NIO.2 API通过Path将BufferedReader转换为File#toPath()，然后使用{{3}来打开File }。
- 还可以看到其他一些可用的API，例如Files#newBufferedReader(Path)（完成操作后不要忘记关闭Stream ）。
您的方法正在 JavaFX Application线程（即UI线程）上执行I / O工作。您永远都不想在FX线程上进行阻塞或长时间运行，因为这会冻结UI，这不是良好的用户体验。考虑将I / O工作移至后台线程，然后将结果发布回FX线程。有关更多信息，请参见Files#lines(Path)和Concurrency in JavaFX软件包。
您需要处理FileChooser#showOpenDialog(Window)返回null的情况。如果用户从对话框中取消，则会发生这种情况。目前，您的代码只会抛出NullPointerException。
请勿将刚刚实例化的随机Stage传递给#showOpenDialog(Window)。您应该传递适当的窗口实例（通常是按钮/任何按钮所属的窗口），以使模式正确运行（即，在显示文件选择器对话框时，防止用户与所有者窗口进行交互）。每个Node都有对其Scene的引用，而该引用也有对其Window的引用。您可以使用load.getScene().getWindow()。

JAVA：线程“ JavaFX应用程序线程”中的异常java.lang.RuntimeException：java.lang.reflect.InvocationTargetException错误

1 个答案: