在 javafx.scene.media.MediaPlayer.init 处使用媒体播放器时出现 Java FX 空指针异常

Question

启动 MediaPlayer 的媒体 block 中没有空字段

我对此进行了广泛的研究，但没有找到任何解释此错误的方法。

我正在为一个类(class)项目构建一个 Java Swing 应用程序，并尝试使用 JFX 面板和媒体播放器来托管和播放多个 mp4 视频。我已经成功地让它工作了一次，但是当我再次回到窗口时，我遇到了错误。

java.lang.NullPointerException at com.sun.media.jfxmediaimpl.platform.gstreamer.GSTMediaPlayer.playerSetBalance(Unknown Source) at com.sun.media.jfxmediaimpl.NativeMediaPlayer.setBalance(Unknown Source) at javafx.scene.media.MediaPlayer.init(Unknown Source) at javafx.scene.media.MediaPlayer.(Unknown Source) at project.screens.TutorialPlayerScreen.initMediaPlayer(TutorialPlayerScreen.java:156) at project.screens.TutorialPlayerScreen.init(TutorialPlayerScreen.java:122) at project.screens.TutorialPlayerScreen.(TutorialPlayerScreen.java:113) at project.buttons.PreKModuleSelectTutorialButtons$Button$7.doAction(PreKModuleSelectTutorialButtons.java:225) at project.screens.PreKModuleSelect.clicked(PreKModuleSelect.java:359) at project.tools.ContentPane.notifiyObserver(ContentPane.java:457) at project.tools.ContentPane$1.mousePressed(ContentPane.java:272) at java.awt.Component.processMouseEvent(Unknown Source) at javax.swing.JComponent.processMouseEvent(Unknown Source) at java.awt.Component.processEvent(Unknown Source) at java.awt.Container.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Window.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEventImpl(Unknown Source) at java.awt.EventQueue.access$500(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source)

这是我用来启动 JFX 媒体的代码:

'//媒体播放器支持 私有(private)组 mediaRoot； 私有(private)场景媒体场景；

private Media tutorialVideo;
private MediaPlayer VideoPlayer;
private MediaView mediaViewer;
private JFXPanel fxPanel;

private int jfxPanelHeight = 394;//525;
private int jfxPanelWidth = 700;//700;

private void initMediaPlayer() throws IOException {
    this.fxPanel = new JFXPanel(); //initializes JFX variables
    fxPanel.setSize(this.jfxPanelWidth ,this.jfxPanelHeight);

    //Add JFX Panel component to the Main Window
    int padding = ((mainWindow.getPreferredSize().width - this.jfxPanelWidth) / 2);
    mainWindow.addLayer(fxPanel, MEDIA_LAYER, padding, 125);

    //Initialize FX Panel
    this.mediaRoot = new Group();
    this.mediaScene = new Scene(this.mediaRoot, 0, 0);

    //Open/prepare the file
    //String tutorialFilePath = new File("").getAbsolutePath() + DIRECTORY_PATH + "Tutorial.mp4";
    String tutorialFilePath = new File("").getAbsolutePath() + MEDIA_PATH + this.observer.getName() +"Tutorial.mp4";
    File mediaFile = new File(tutorialFilePath);
    this.tutorialVideo = new Media(mediaFile.toURI().toString());

    //Create the media player
    this.VideoPlayer = new MediaPlayer(this.tutorialVideo);  //Error here
    this.VideoPlayer.setAutoPlay(false);

    this.mediaViewer = new MediaView(this.VideoPlayer);
    this.mediaViewer.setFitHeight(this.jfxPanelHeight);
    this.mediaViewer.setFitWidth(this.jfxPanelWidth);
          ((Group)this.mediaScene.getRoot()).getChildren().add(this.mediaViewer);

    fxPanel.setScene(this.mediaScene);
}'

我尝试在离开屏幕之前清理已用的内存。

public void tearDown(){

    //Stop the JFX Player and Remove
    this.mainWindow.removeLayer(this.fxPanel);
    this.VideoPlayer.stop();
    this.VideoPlayer.dispose();
    this.fxPanel.removeAll();
    this.mediaRoot.getChildren().removeAll();

    this.mediaRoot = null;
    this.mediaScene = null;
    this.mediaViewer = null;
    this.tutorialVideo  = null;
    this.VideoPlayer = null;
    this.fxPanel = null;
}

private JLayeredPane contentPane;    //The content pane of this JFrame.
public void removeLayer(JComponent component) {
    contentPane.remove(component);
    contentPane.revalidate();
    contentPane.repaint();
}

任何帮助或评论将不胜感激!谢谢!

Answer 1

您的代码中存在线程问题，需要修复。具体来说，您必须创建 FX UI 组件并在 FX 应用程序线程上设置场景图。请参阅Javadocs for JFXPanel了解详情。

然而，这是空指针异常的附带情况。我认为造成这种情况的原因是，当您从 UI 中完全删除 JFXPanel 时，FX 工具包将关闭。为了防止这种情况，只需调用

Platform.setImplicitExit(false);

当您首次初始化应用程序时。 (此方法可以安全地从任何线程调用。)

这是一个类似的 SSCCE:

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.FlowLayout;

import javafx.application.Platform;
import javafx.embed.swing.JFXPanel;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javafx.scene.media.MediaView;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;


public class MediaPlayerInSwing {

    private static final String MEDIA_URL = "http://download.oracle.com/otndocs/products/javafx/oow2010-2.flv" ;

    private JFrame window ;

    private JFXPanel jfxPanel ;
    private Media media ;
    private MediaPlayer player ;
    private MediaView mediaView ;
    private BorderPane root ;
    private Scene scene ;

    private Button button ;

    // create on AWT Event Dispatch Thread
    public MediaPlayerInSwing() {
        Platform.setImplicitExit(false);
        initGUI();
    }

    private void initGUI()  {
        window = new JFrame();
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setLayout(new BorderLayout());

        JPanel controls = new JPanel();
        controls.setLayout(new FlowLayout());
        button = new Button("Show video");
        controls.add(button);
        button.addActionListener(e -> {
            if (jfxPanel == null) {
                showVideo();
            } else {
                tearDownVideo();
            }
        });

        window.add(controls, BorderLayout.SOUTH);
        window.setSize(600, 480);
        window.setLocationRelativeTo(null);
        window.setVisible(true);
    }

    private void showVideo() {


        jfxPanel = new JFXPanel();

        Platform.runLater(() -> {
            media = new Media(MEDIA_URL);
            player = new MediaPlayer(media);
            player.play(); 
            mediaView = new MediaView(player);
            root = new BorderPane(mediaView);
            scene = new Scene(root, 600, 400);
            jfxPanel.setScene(scene);
        });

        window.add(jfxPanel, BorderLayout.CENTER);
        button.setLabel("Hide video");
    }

    private void tearDownVideo() {

        window.remove(jfxPanel);

        Platform.runLater(() -> {
            player.stop();
            player.dispose();
            player = null ;
            mediaView = null ;
            root = null ;
            jfxPanel.setScene(null);
            scene = null ;
            SwingUtilities.invokeLater(() -> {
                jfxPanel = null ;
                // force window to repaint...
                window.getRootPane().repaint();
            });
        });
        button.setLabel("Show video");
    }

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeLater(MediaPlayerInSwing::new);
    }
}