類檔案JavaFX中不兼容的魔法值-有解無憂

我需要實作 tabulate 函式（使用 MenuItem TabulateFunction），它以位元組碼的形式位于一個擴展名為 .class 的檔案中。由于函式可以擁有實作我的介面的三個類之一，那么，根據任務，您需要實作一個單獨的類，該類將負責從檔案中讀取位元組碼并基于該位元組創建一個物件-代碼。

我創建了一個 ClassLoaderForFunctions 類并return defineClass在其中使用，這就是問題所在。當我在選單中選擇 Tabulate Function 時，它會呼叫 ClassLoaderForFunctions 中的方法，該方法為檔案中的函式實作了上述內容。

當涉及到時return defineClass，我收到一個錯誤：執行緒中的例外JavaFX Application Thread" java.lang.ClassFormatError: Incompatible magic value 11 in class file tlog/class

在 Main 類中，我呼叫控制器并將tlog物件的位元組碼寫入擴展名為 .class 的檔案中

*為了堆疊跟蹤，我洗掉了匯入行

可能是什么問題呢？

ClassLoaderForFunctions：

package JavaFX_Application;

public class ClassLoaderForFunctions extends ClassLoader{

    public Class<?> loadClassFromFile(File file) throws IOException {
    FileInputStream in = new FileInputStream(file);
    byte[] fileContent = new byte[in.available()]; //available - возвращает количество байтов ввода, доступные в данный момент для чтения
    in.read(fileContent);
    in.close();

    return defineClass(file.getName(), fileContent, 0, fileContent.length);
}

}

FXMLMainFormController：

        package JavaFX_Application;

   


    public class FXMLMainFormController implements Initializable {

        public static TabulatedFunctionDoc tabFDoc = new TabulatedFunctionDoc();
        private Stage MainStage;
        private File file;
        private ClassLoaderForFunctions Loader;
        private FXMLMenuController ctrl;
        private Alert dialog;

        @FXML
        private MenuItem TabulateFunction;

        @FXML
        private MenuItem NewFunction;
    
        @FXML
        private MenuItem FileClose;

        @FXML
        private MenuItem OpenFile;

        @FXML
        private MenuItem SaveFile;

        @FXML
        private MenuItem SaveFileAs;

        @FXML
        private TableView<FunctionPointT> table = new TableView<>();

        @FXML
        private Label point_count;

        @FXML
        private TextField edX = new TextField(),edY = new TextField();

        @FXML
        private TableColumn<FunctionPointT,Double> columnX = new         TableColumn<FunctionPointT,Double>("X");;

        @FXML
        private TableColumn<FunctionPointT,Double> columnY = new         TableColumn<FunctionPointT,Double>("Y");;

        @FXML
        private void deletePoint(ActionEvent event) throws IOException {
            if (isSelected()) {
                tabFDoc.deletePoint(getIndex() - 1);
            } else {
                if(tabFDoc.getPointsCount() > 2)
                    tabFDoc.deletePoint(tabFDoc.getPointsCount() - 1);
                else
                    showDialog("Length of Document < 3","Please add some point or stop         trying to delete point");

            }
        }

        @FXML
        private void addPoint(ActionEvent event) throws         InappropriateFunctionPointException, IOException {
            if(!edX.getText().isEmpty() && !edY.getText().isEmpty()) {
                tabFDoc.addPoint(new FunctionPoint(Double.parseDouble(edX.getText()),         Double.parseDouble(edY.getText())));
            }
            edX.setText("");
            edY.setText("");
            //table.getItems().add(new         FunctionPointT(Double.parseDouble(edX.getText()),Double.parseDouble(edY.getText()))); //         добавляем строку
        }

        @FXML
        public void redraw(){
            if(!table.getColumns().isEmpty())
                table.getItems().clear();
            ObservableList<FunctionPointT> data = table.getItems();
            for(int i = 0;i< tabFDoc.getPointsCount();    i) {
                data.add(new         FunctionPointT(tabFDoc.getLink().getPointX(i),tabFDoc.getLink().getPointY(i)));
            }
            if (isSelected()) {
                point_count.setText("Point "   getIndex()   " of "   tabFDoc.getPointsCount());
            } else {
                point_count.setText("Point "   tabFDoc.getPointsCount()   " of "           tabFDoc.getPointsCount());
            }
        }

        @FXML
        private void setSelectedIndexByKey(){
            point_count.setText("Point "   getIndex()   " of "           tabFDoc.getPointsCount());
        }

        @FXML
        private void setSelectedIndexByClick() {
            if(isSelected() && tabFDoc !=null)
                point_count.setText("Point "   getIndex()   " of "           tabFDoc.getPointsCount());
        }

        private void openWindow() throws IOException {
            Stage primaryStage = new Stage();
            FXMLLoader loader = new FXMLLoader(getClass().getResource("FXMLMenu.fxml"));
            Parent root = loader.load();
            ctrl = loader.getController();
            ctrl.setMainController(this);

            primaryStage.setTitle("Create New Function");
            primaryStage.setScene(new Scene(root));
            primaryStage.setResizable(false);

            primaryStage.initModality(Modality.APPLICATION_MODAL);
            primaryStage.initOwner(MainStage);
            primaryStage.setOnCloseRequest(windowEvent -> {
                windowEvent.consume();
            });
            primaryStage.showAndWait();
        }

        private void SaveFunctionAs() throws IOException {
            FileChooser fileChooser = new FileChooser();
            fileChooser.setTitle("Open file");
            fileChooser.getExtensionFilters().add(new FileChooser.ExtensionFilter("Text         files", "*.json"));
            file = fileChooser.showSaveDialog(table.getScene().getWindow());
            if(file!=null) {
                tabFDoc.saveFunctionAs(file.getName());
            }
        }

        @Override
        public void initialize(URL url, ResourceBundle resourceBundle) {
            dialog = new Alert(Alert.AlertType.ERROR);
            tabFDoc.setController(this);
            columnX.setCellValueFactory(new PropertyValueFactory<FunctionPointT,Double>        ("X"));
            table.getColumns().add(columnX);
            columnY.setCellValueFactory(new PropertyValueFactory<FunctionPointT,Double>        ("Y"));
            table.getColumns().add(columnY);
            table.setPrefWidth(573.0);
            table.setPrefHeight(220.0);
            columnY.setPrefWidth(286.5);
            columnX.setPrefWidth(286.5);
            Loader = new ClassLoaderForFunctions();
            ObservableList<FunctionPointT> data = table.getItems();
            for(int i = 0;i< tabFDoc.getPointsCount();    i) {
                data.add(new         FunctionPointT(tabFDoc.getLink().getPointX(i),tabFDoc.getLink().getPointY(i)));
            }

            NewFunction.setOnAction(event -> {
                try {
                    openWindow();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            });
            OpenFile.setOnAction(event ->{
                FileChooser fileChooser = new FileChooser();
                fileChooser.setTitle("Open file");
                fileChooser.getExtensionFilters().add(new         FileChooser.ExtensionFilter("Text files", "*.json"));
                file = fileChooser.showOpenDialog(table.getScene().getWindow());
                if(file!=null) {
                    tabFDoc.loadFunction(file.getName());
                    redraw();
                }
            });
            FileClose.setOnAction(event ->{
                MainStage.close();
            });
            SaveFile.setOnAction(event ->{
                try {
                    tabFDoc.saveFunction();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            });
            SaveFileAs.setOnAction(event -> {
                try {
                    SaveFunctionAs();
                } catch (IOException e) {
                   e.printStackTrace();
                }
            });
            TabulateFunction.setOnAction(event->{
                try {
                    FileChooser fileChooser = new FileChooser();
                    fileChooser.setTitle("Open class");
                    fileChooser.getExtensionFilters().add(new         FileChooser.ExtensionFilter("Class files", "*.class"));
                    file = fileChooser.showOpenDialog(table.getScene().getWindow());
                    //tabFDoc.setFunction((Function)         Loader.loadClassFromFile(file).getConstructor().newInstance());
                    if (file != null) {
                        openWindow();
                        if(ctrl.getLeftDomainBorderBorder() != Double.POSITIVE_INFINITY         && ctrl.getRightDomainBorderBorder() != Double.NEGATIVE_INFINITY && ctrl.getPointsCount() >         2) {
                            tabFDoc.tabulateFunction((Function)         Loader.loadClassFromFile(file).getConstructor().newInstance(),         ctrl.getLeftDomainBorderBorder(), ctrl.getRightDomainBorderBorder(), ctrl.getPointsCount());
                            redraw();
                        }
                    }
                }
                catch (Exception e) {
                }
            });


        }

        public boolean isSelected(){
            return (table.getSelectionModel().getSelectedItem() != null);
        }

        private int getIndex(){
            int index = 0;
            if (isSelected()) {
                for (int i = 0; i < tabFDoc.getPointsCount();   i) {
                    if (table.getSelectionModel().getSelectedItem().getX() ==         tabFDoc.getLink().getPointX(i) && table.getSelectionModel().getSelectedItem().getY() ==         tabFDoc.getLink().getPointY(i))
                        index = i   1;
                }
            }
            return index  ;
        }

        public void setStage(Stage stage){
            MainStage = stage;
        }

        public Stage getStage(){
            return MainStage;
        }

        public TabulatedFunctionDoc getTabFDoc(){
            return tabFDoc;
        }

        public void showDialog(String header, String message) {

            dialog.setHeaderText(header);
            dialog.setTitle("Error");
            dialog.setContentText(message);
            dialog.showAndWait();

        }

    }

表格函式檔案：

package JavaFX_Application;

import functions.*;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

public class TabulatedFunctionDoc implements TabulatedFunction {
    private TabulatedFunction Link;
    private String fileName = "";
    private boolean modified = false;
    private boolean fileNameAssigned = false;
    private FXMLMainFormController controller;
    private Function function = null;


    public TabulatedFunctionDoc() {
        Link = new ArrayTabulatedFunction(-1, 1, 2);
    }

    public void setFunction(Function input_function){
        function = input_function;
    }

public void setController(FXMLMainFormController ctrl) {
    this.controller = ctrl;
}

public void CallRedraw() throws IOException {
    if(registerRedrawFunctionController(controller))
        controller.redraw();
}

public TabulatedFunction getLink() {
    return Link;
}

public boolean registerRedrawFunctionController(FXMLMainFormController ctrl) {
    return ctrl.getStage().isShowing();
}

public boolean isModified() {
    return modified;
}

public boolean isFileNameAssigned() {
    return fileNameAssigned;
}

public void newFunction(double leftX, double rightX, int pointsCount) throws IOException {
    Link = new ArrayTabulatedFunction(leftX, rightX, pointsCount);
    modified = false;
}

public void tabulateFunction(Function function, double leftX, double rightX, int pointsCount) {
    Link = TabulatedFunctions.tabulate(function, leftX, rightX, pointsCount);
    modified = false;
}

public void saveFunctionAs(String fileName) throws IOException {
    this.fileName = fileName;
    fileNameAssigned = true;
    saveFunction();
    modified = false;
}

public void loadFunction(String fileName) {
    this.fileName = fileName;
    fileNameAssigned = true;

    JSONParser jsonParser = new JSONParser();

    try (FileReader reader = new FileReader(fileName))
    {
        Object obj = jsonParser.parse(reader);
        JSONArray employeeList = (JSONArray) obj;
        FunctionPoint[] array = new FunctionPoint[employeeList.size()];
        //System.out.println(employeeList);
        for(int i = 0; i < employeeList.size();    i){

            JSONObject employeeObject = (JSONObject)((JSONObject)employeeList.get(i)).get("Точки");

            array[i] = new FunctionPoint((Double) employeeObject.get("X"),(Double) employeeObject.get("Y"));
        }
        this.Link = new ArrayTabulatedFunction(array);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ParseException e) {
        e.printStackTrace();
    }
    modified = false;
}

public void saveFunction() throws IOException {

    JSONArray Link = new JSONArray();

    for(int i =0; i < this.Link.getPointsCount();   i){
        JSONObject point = new JSONObject();
        point.put("X",this.Link.getPointX(i));
        point.put("Y",this.Link.getPointY(i));
        JSONObject points = new JSONObject();
        points.put("Точки",point);
        Link.add(points);
    }
    FileWriter fileWriter = new FileWriter(fileName);
    fileWriter.write(Link.toJSONString());
    fileWriter.flush();
    modified = false;

}

@Override
public int getPointsCount() {
    return this.Link.getPointsCount();
}

@Override
public void setPointY(int index, double y) throws IOException {
    this.Link.setPointY(index, y);
    this.modified = true;
    CallRedraw();
}

@Override
public double getPointY(int index) {
    return this.Link.getPointY(index);
}

@Override
public double getPointX(int index) {
    return this.Link.getPointX(index);
}

@Override
public double getFunctionValue(double x) {
    return this.Link.getFunctionValue(x);
}

@Override
public void addPoint(FunctionPoint point) throws InappropriateFunctionPointException, IOException {
    this.modified = true;
    this.Link.addPoint(point);
    CallRedraw();
}

@Override
public void setPoint(int index, FunctionPoint point) throws InappropriateFunctionPointException, IOException {
    this.Link.setPoint(index, point);
    this.modified = true;
    CallRedraw();
}

@Override
public void setPointX(int index, double x) throws InappropriateFunctionPointException, IOException {
    this.Link.setPointX(index, x);
    this.modified = true;
    CallRedraw();
}

@Override
public void deletePoint(int index) throws IOException {
    this.Link.deletePoint(index);
    this.modified = true;
    CallRedraw();
}

@Override
public double getRightDomainBorder() {
    return this.Link.getRightDomainBorder();
}

@Override
public double getLeftDomainBorder() {
    return this.Link.getLeftDomainBorder();
}

@Override
public FunctionPoint getPoint(int index) {
    if (index >= 0 && index < this.getPointsCount()) {
        return new FunctionPoint(this.Link.getPoint(index));
    } else {
        throw new FunctionPointIndexOutOfBoundsException();
    }
}
}

堆疊跟蹤：

Exception in thread "JavaFX Application Thread" java.lang.ClassFormatError: Incompatible magic value 11 in class file tlog/class
    at java.base/java.lang.ClassLoader.defineClass1(Native Method)
    at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1010)
    at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:872)
    at JavaFX_Application.ClassLoaderForFunctions.loadClassFromFile(ClassLoaderForFunctions.java:15)
    at JavaFX_Application.FXMLMainFormController.lambda$initialize$6(FXMLMainFormController.java:206)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.controls/javafx.scene.control.MenuItem.fire(MenuItem.java:459)
    at javafx.controls/com.sun.javafx.scene.control.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1385)
    at javafx.controls/com.sun.javafx.scene.control.ContextMenuContent$MenuItemContainer.lambda$createChildren$12(ContextMenuContent.java:1338)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
    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$MouseHandler.process(Scene.java:3897)
    at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1878)
    at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2623)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
    at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:557)
    at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:943)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
    at java.base/java.lang.Thread.run(Thread.java:831)

uj5u.com熱心網友回復：

您顯然想要做的是生成一個.class檔案，然后您可以加載該檔案。

但問題是您實際寫入“tlog.class”的內容不是標準類檔案格式。實際上，看起來您只是在使用DataOutputStream方法撰寫一堆數字。這甚至遠不接近有效的¹。

無論如何，當您嘗試加載（假設的）類檔案時，JVM 會說，實際上：

“不！那不是有效的類檔案格式。它甚至沒有以正確的幻數開頭！”

那么解決方案是什么？

那么你可以（理論上）生成一個有效的類檔案。問題是創建一個有效的類檔案來實作你的函式會很困難，并且需要深入了解 Java 位元組碼和類檔案的結構。并且不清楚您是否會通過這樣做來實作任何目標。

這里有幾個（可能）更好的想法。

只需將資料作為資料檔案讀取和寫入即可。然后使用從檔案中讀取的資料撰寫一些實作所需功能的 Java 代碼。
撰寫一些 Java 代碼來為函式生成 Java 源代碼，將資料作為常量陣列或其他內容嵌入檔案中。然后呼叫Java編譯器進行編譯，并加載生成的.class檔案。

第一個選項是最簡單的，而且很可能是您需要的所有選項。如果該功能對性能至關重要，您可能會考慮第二個選項。但是，只有在測量了性能后才應該這樣做。此外，您可能會發現加速比很小，并且不值得為實作它而付出相當大的努力。

^{1 - 該格式記錄在JVM 規范的第 4 章中。您需要了解更多規范才能撰寫類方法和偽方法的位元組碼。}

轉載請註明出處，本文鏈接：https://www.uj5u.com/yidong/361196.html

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