我有一个创建视频播放器的类（代码附在下面），这个类只适用于视频文件。我想要播放没有视频文件的播放器，当我发送到对象时，通过公共方法“setFile”，它将开始播放。
我试图发送“null”而不是文件到这个类，但我得到一个错误（“java.lang.NullPointerException”）。
VideoPlayer player = new VideoPlayer(null, videoWidth, videoHeight);
而错误：
Exception in Application start method
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(Unknown Source)
at com.sun.javafx.application.LauncherImpl.launchApplication(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.launcher.LauncherHelper$FXHelper.main(Unknown Source)
Caused by: java.lang.RuntimeException: Exception in Application start method
at com.sun.javafx.application.LauncherImpl.launchApplication1(Unknown Source)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$152(Unknown Source)
at com.sun.javafx.application.LauncherImpl$$Lambda$51/1323468230.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.IllegalArgumentException: uri.getScheme() == null! uri == ''
at com.sun.media.jfxmedia.locator.Locator.<init>(Unknown Source)
at javafx.scene.media.Media.<init>(Unknown Source)
at v04.VideoPlayer.setFile(VideoPlayer.java:90)
at v04.VideoPlayer.<init>(VideoPlayer.java:40)
at v04.MainFrame.setVideoPlayer(MainFrame.java:218)
at v04.MainFrame.createVideoPane(MainFrame.java:246)
at v04.MainFrame.start(MainFrame.java:112)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$159(Unknown Source)
at com.sun.javafx.application.LauncherImpl$$Lambda$54/539248128.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$172(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$47/186276003.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$null$170(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$49/1850153616.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$48/237061348.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$145(Unknown Source)
at com.sun.glass.ui.win.WinApplication$$Lambda$37/2117255219.run(Unknown Source)
我也尝试创建没有文件的Media :(同样的错误）
media = new Media(videoFile.toURI().toString());
mediaPlayer = new MediaPlayer(null);
mediaView = new MediaView(mediaPlayer);
班级：
import java.io.File;
import javafx.beans.property.DoubleProperty;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.Slider;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.layout.Region;
import javafx.scene.layout.StackPane;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javafx.scene.media.MediaView;
import javafx.util.Duration;
public class VideoPlayer extends GridPane {
File videoFile;
Media media;
MediaPlayer mediaPlayer;
MediaView mediaView;
DoubleProperty width;
DoubleProperty height;
VideoPlayer(File file, double width, double height) {
setHgap(10);
setVgap(10);
setPadding(new Insets(10, 10, 10, 10));
setFile(file);
mediaView.setFitHeight(height*0.80);
mediaView.setFitWidth(width*0.80);
mediaView.setPreserveRatio(true);
add(mediaView, 1, 0);
add(setSlider(),1,1);
}
public HBox setSlider() {
// Play and pause button
Button playButton = new Button("Play");
playButton.setOnAction(e -> {
if (playButton.getText().equals("Play")) {
mediaPlayer.play();
playButton.setText("pause");
} else {
mediaPlayer.pause();
playButton.setText("Play");
}
});
// Rewind button
Button rewindButton = new Button("rewind");
rewindButton.setOnAction(e -> mediaPlayer.seek(Duration.ZERO));
// Slieder for volume
Slider slVolume = new Slider();
slVolume.setPrefWidth(150);
slVolume.setMaxWidth(Region.USE_PREF_SIZE);
slVolume.setMinWidth(30);
slVolume.setValue(50);
mediaPlayer.volumeProperty().bind(slVolume.valueProperty().divide(100));
HBox hBox = new HBox(10);
hBox.setAlignment(Pos.CENTER);
hBox.getChildren().addAll(playButton, rewindButton,
new Label("Volume"), slVolume);
return hBox;
}
public void setFile(File file) {
videoFile=file;
videoFile = file;
media = new Media(videoFile.toURI().toString());
mediaPlayer = new MediaPlayer(media);
mediaView = new MediaView(mediaPlayer);
width = mediaView.fitWidthProperty();
height = mediaView.fitHeightProperty();
}
public void playVideo() {
mediaPlayer.play();
}
}
当您将null参数传递给构造函数的第一个arg时，会将其传递给setFile，如下所示：setFile(null)
这个功能有：
public void setFile(File file) {
videoFile = file;
videoFile = file; // You are doing this twice? Is this an error on your part?
media = new Media(videoFile.toURI().toString()); // This is where the null pointer is happening.
}
videoFile为null，您在null对象上调用toURI()。
我不知道这是否能完全解决你的问题，但除非你改变你的代码 - 你需要像这样防范空值：
public void setFile(File file) {
if (file == null)
return;
videoFile = file;
media = new Media(videoFile.toURI().toString());
mediaPlayer = new MediaPlayer(media);
mediaView = new MediaView(mediaPlayer);
width = mediaView.fitWidthProperty();
height = mediaView.fitHeightProperty();
}