java - 如何将滚动 Pane 内容保存为 jpg 文件

Question

下面是我的代码，我尝试将 ScrollPane 内容保存为 jpg 文件。它给了我一个 IllegalArgumentException 错误。到目前为止我已经尝试过 this和 this ，但显然我将错误的参数放入 ImageIO.write 方法中。我在这里缺少什么？

    package urd.View;

    import java.awt.image.BufferedImage;
    import java.io.File;
    import java.io.IOException;
    import java.util.logging.Level; 
    import java.util.logging.Logger;
    import javafx.application.Application;
    import static javafx.application.Application.launch;
    import javafx.embed.swing.SwingFXUtils;
    import javafx.event.ActionEvent; 
    import javafx.scene.Scene;
    import javafx.scene.SnapshotParameters;
    import javafx.scene.control.Menu;
    import javafx.scene.control.MenuBar;
    import javafx.scene.control.MenuItem;
    import javafx.scene.control.ScrollPane;
    import javafx.scene.image.WritableImage;
    import javafx.scene.layout.BorderPane;
    import javafx.scene.layout.Pane; 
    import javafx.scene.paint.Color;
    import javafx.scene.shape.Circle;
    import javafx.scene.shape.Rectangle;
    import javafx.stage.Stage;
    import javax.imageio.ImageIO;
    import javax.swing.JFileChooser;

    /**
    *
    * @author urd
    */
    public class NewFXMain extends Application {

private final int width = 250;
private final int height = 250;

private final int radius = 15;
double circleX = width / 2;
double circleY = height / 2;
Circle circle = new Circle(circleX, circleY, radius);

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    launch(args);
}

/**
 * @param primaryStage the command line arguments
 */
@Override
public void start(Stage primaryStage) {
    BorderPane rootPane = new BorderPane();
    ScrollPane scrollPane = new ScrollPane();
    MenuBar menuBar = new MenuBar();
    Menu fileMenu = new Menu("File");
    Menu generator = new Menu("generate");
    MenuItem generateItem = new MenuItem("generate");
    menuBar.getMenus().addAll(fileMenu, generator);
    MenuItem saveItem = new MenuItem("Save Image");
    fileMenu.getItems().addAll(saveItem);
    generator.getItems().addAll(generateItem);
    rootPane.setTop(menuBar);
    rootPane.setCenter(scrollPane);
    Scene scene = new Scene(rootPane, 400, 350);
    primaryStage.setTitle("Image Generator");
    primaryStage.setScene(scene);
    primaryStage.show();
    saveItem.setOnAction((ActionEvent event) -> {
        // the content of scrollPane is saved as a JPEG file.
        WritableImage img = scrollPane.snapshot(new SnapshotParameters(), null);
        JFileChooser chooser = new JFileChooser();
        chooser.setCurrentDirectory(new File(System.getProperty("user.home")));
        File fileToSave = chooser.getSelectedFile();
        BufferedImage img2 = SwingFXUtils.fromFXImage(img, null);
        int result = chooser.showSaveDialog(null);
        if (result == JFileChooser.APPROVE_OPTION) {
            try {
                ImageIO.write(img2, "png", fileToSave);
            } catch (IOException ex) {
                Logger.getLogger(GuiClass.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
    });
    generateItem.setOnAction((ActionEvent event) -> {
        //Here we call the generateImage method which takes in two int values and returns a pane
        scrollPane.setContent(generateImage());
    });
}

private Pane generateImage() {
    Rectangle rectCanvas = new Rectangle(width,
        height);
    rectCanvas.setFill(Color.GREEN);
    circle.setFill(Color.RED);
    Pane pane = new Pane();
    pane.getChildren().addAll(rectCanvas, circle);
    return pane;
}

}

这是IllegalArgumentException的日志

    Exception in thread "JavaFX Application Thread" java.lang.IllegalArgumentException: output == null!
at javax.imageio.ImageIO.write(ImageIO.java:1516)
at urd.View.NewFXMain.lambda$start$0(NewFXMain.java:86)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.control.MenuItem.fire(MenuItem.java:462)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1405)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.lambda$createChildren$343(ContextMenuContent.java:1358)
at com.sun.javafx.event.CompositeEventHandler$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$MouseEventNotification.run(GlassViewEventHandler.java:381)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:417)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)

Answer 1

chooser.getSelectedFile() 在调用 showSaveDialog() 后返回 File 对象，因此在调用 showSaveDialog() 方法后创建文件对象，如下所示。

    saveItem.setOnAction((ActionEvent event) -> {
                // the content of scrollPane is saved as a JPEG file.
                WritableImage img = scrollPane.snapshot(new SnapshotParameters(), null);
                JFileChooser chooser = new JFileChooser();
                chooser.setCurrentDirectory(new File(System.getProperty("user.home")));
               // File fileToSave = chooser.getSelectedFile();//Remove this line.
                BufferedImage img2 = SwingFXUtils.fromFXImage(img, null);
                int result = chooser.showSaveDialog(null);
                if (result == JFileChooser.APPROVE_OPTION) {
                    try {
                        File fileToSave = chooser.getSelectedFile();
                        ImageIO.write(img2, "png", fileToSave);
                    } catch (IOException ex) {
                        Logger.getLogger(GuiClass.class.getName()).log(Level.SEVERE, null, ex);
                    }
                }
            });