如何在没有监听器的情况下获取javafx媒体元数据

Question

所以我一直在寻找这个一周,并且阅读虽然每个问题都很相似,但似乎没有人像我一样问同样的问题(尝试逆向工程其他解决方案类似于我想要的但没有成功.

解释了穴居人风格:我正在尝试使用元数据创建列表.

1. 我用多个对话框打开并选择多个mp3
2. 我把文件放在一个 ArrayList<File>
3. 我循环使用增强的for循环文件,并使用媒体变量提取元数据
4. 例如,我想要保存在ArrayList中的元数据信息(如"artist")

问题是,只有在增强循环完成后,侦听器才会起作用,导致 ArrayList<String>一个对象中没有任何内容

这是一个示例:

ArrayList<String> al;
String path;
public void open(){
    files=chooser.showOpenMultipleDialog(new Stage());
    for( File f:files){             
        path=f.getPath();
        Media media = new Media("file:/"+path.replace("\\", "/").replace(" ", "%20"));
        al= new ArrayList<String>();
        media.getMetadata().addListener(new MapChangeListener<String, Object>() {                 
            public void onChanged(Change<? extends String, ? extends Object> change) {
                if (change.wasAdded()) {
                    if (change.getKey().equals("artist")) {
                        al.add((String) change.getValueAdded());
                     }
                }
            }
        });
    }//close for loop
    //then i want to see the size of al like this
    system.out.println(al.size());
    //then it returns 1 no matter how much file i selected
    //when i system out "al" i get an empty string

Answer 1

通过添加侦听器来读取媒体源元数据的另一种方法是在 mediaplayer .setOnReady() 中提取该信息；这是 java 控制器类的示例部分

公共类 uiController 实现可初始化 {

@FXML private Label label;
@FXML private ListView<String> lv;
@FXML private AnchorPane root;
@FXML private Button button;

private ObservableList<String> ol= FXCollections.observableArrayList();
private List<File> selectedFiles;
private final Object obj= new Object();

@Override
public void initialize(URL url, ResourceBundle rb) {
    assert button != null : "fx:id=\"button\" was not injected: check your FXML file 'ui.fxml'.";
    assert label != null : "fx:id=\"label\" was not injected: check your FXML file 'ui.fxml'.";
    assert lv != null : "fx:id=\"lv\" was not injected: check your FXML file 'ui.fxml'.";
    assert root != null : "fx:id=\"root\" was not injected: check your FXML file 'ui.fxml'.";

    // initialize your logic here: all @FXML variables will have been injected
    lv.setItems(ol);
}  

@FXML private void open(ActionEvent event) {
    FileChooser.ExtensionFilter extention= new FileChooser.ExtensionFilter("Music Files", "*.mp3","*.m4a","*.aif","*.wav","*.m3u","*.m3u8");
    FileChooser fc= new FileChooser();
    fc.setInitialDirectory(new File(System.getenv("userprofile")));
    fc.setTitle("Select File(s)");
    fc.getExtensionFilters().add(extention);
    selectedFiles =fc.showOpenMultipleDialog(root.getScene().getWindow());
    if(selectedFiles != null &&!selectedFiles.isEmpty()){
        listFiles();
    }
}
/**
 * Convert each fie selected to its URI
 */
private void listFiles(){ 
    try {
        for (File file : selectedFiles) {
            readMetaData(file.toURI().toString());
            synchronized(obj){
               obj.wait(100);
            }
        }
    } catch (InterruptedException ex) {
    }
    System.gc();
}
/**
 * Read a Media source metadata 
 * Note: Sometimes the was unable to extract the metadata especially when 
 * i have selected large number of files reasons i don't known why
 * @param mediaURI Media file URI
 */
private void readMetaData(String mediaURI){
    final MediaPlayer mp= new MediaPlayer(new Media(mediaURI));
    mp.setOnReady(new Runnable() {

        @Override
        public void run() {
            String artistName=(String) mp.getMedia().getMetadata().get("artist");
            ol.add(artistName);
            synchronized(obj){//this is required since mp.setOnReady creates a new thread and our loopp  in the main thread
                obj.notify();// the loop has to wait unitl we are able to get the media metadata thats why use .wait() and .notify() to synce the two threads(main thread and MediaPlayer thread)
            }
        }
    });
}

}

所做的一些更改是使用 ObservableList 来存储元数据中的艺术家姓名

在代码中你会发现这个

同步（对象）{
                    obj.等待(100);
                }

我这样做是因为 mediaplayer .setOnReady() 创建了一个新线程，并且循环位于主应用程序线程中，该循环必须等待一段时间才能创建另一个线程，我们才能提取元数据，并且在.setOnReady() 有一个

同步（对象）{
                    obj.通知；
                }

唤醒主线程，因此循环能够移动到下一个项目

我承认这可能不是最好的解决方案，但欢迎任何有更好方法从文件列表中读取 JavaFx 媒体元数据的人。完整的 Netbeans 项目可以在这里找到https://docs.google .com/file/d/0BxDEmOcXqnCLSTFHbTVFcGIzT1E/edit?usp=sharing

plus 使用 JavaFX 创建了一个小型 MediaPlayer 应用程序，该应用程序利用元数据https://docs.google.com/file/d/0BxDEmOcXqnCLR1Z0VGN4ZlJkbUU/edit?usp=sharing