在这里我修改了getPlayList（）方法。

ArrayList<HashMap<String,String>> getPlayList(String rootPath) {
            ArrayList<HashMap<String,String>> fileList = new ArrayList<>();

            try {
                File rootFolder = new File(rootPath);
                File[] files = rootFolder.listFiles(); //here you will get NPE if directory doesn't contains  any file,handle it like this.
                for (File file : files) {
                    if (file.isDirectory()) {
                        if (getPlayList(file.getAbsolutePath()) != null) {
                            fileList.addAll(getPlayList(file.getAbsolutePath()));
                        } else {
                            break;
                        }
                    } else if (file.getName().endsWith(".mp3")) {
                        HashMap<String, String> song = new HashMap<>();
                        song.put("file_path", file.getAbsolutePath());
                        song.put("file_name", file.getName());
                        fileList.add(song);
                    }
                }
                return fileList;
            } catch (Exception e) {
                return null;
            }
        }

您可以获得歌曲名称和歌曲路径，如下所示：

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_activity);
ArrayList<HashMap<String,String>> songList=getPlayList("/storage/sdcard1/");
        if(songList!=null){
        for(int i=0;i<songList.size();i++){
        String fileName=songList.get(i).get("file_name");
        String filePath=songList.get(i).get("file_path");
        //here you will get list of file name and file path that present in your device
        log.e("file details "," name ="+fileName +" path = "+filePath);
        }
        }
    }

**注意：**使用“/storage/sdcard 1/”从sdCard阅读文件，使用Environment.getExternalStorageDirectory（）.getAbsolutePath（）从手机存储器读取文件

希望这对你有帮助。

希望你已经找到了你的答案，但可能这是更好的，如果你想尝试，这里是你的解决方案使用下面的代码从特定文件夹或所有文件中读取MP3文件，
首先创建1个模型类，如下所示，到列表中的GET和SET文件。
AudioModel.class

public class AudioModel {

    String aPath;
    String aName;
    String aAlbum;
    String aArtist;

    public String getaPath() {
        return aPath;
    }

    public void setaPath(String aPath) {
        this.aPath = aPath;
    }

    public String getaName() {
        return aName;
    }

    public void setaName(String aName) {
        this.aName = aName;
    }

    public String getaAlbum() {
        return aAlbum;
    }

    public void setaAlbum(String aAlbum) {
        this.aAlbum = aAlbum;
    }

    public String getaArtist() {
        return aArtist;
    }

    public void setaArtist(String aArtist) {
        this.aArtist = aArtist;
    }
}

现在我们有我们的模型类，使用下面的代码来读取所有的MP3文件从您的文件夹或设备.
这将返回包含音乐的所有MP3文件的列表NAME, PATH, ARTIST, ALBUM。如果您想了解更多详细信息，请参阅documentation for Media.Store.Audio

public List<AudioModel> getAllAudioFromDevice(final Context context) {

        final List<AudioModel> tempAudioList = new ArrayList<>();

        Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
        String[] projection = {MediaStore.Audio.AudioColumns.DATA, MediaStore.Audio.AudioColumns.ALBUM, MediaStore.Audio.ArtistColumns.ARTIST,};
        Cursor c = context.getContentResolver().query(uri, projection, MediaStore.Audio.Media.DATA + " like ? ", new String[]{"%yourFolderName%"}, null);

        if (c != null) {
            while (c.moveToNext()) {

                AudioModel audioModel = new AudioModel();
                String path = c.getString(0);
                String album = c.getString(1);
                String artist = c.getString(2);

                String name = path.substring(path.lastIndexOf("/") + 1);

                audioModel.setaName(name);
                audioModel.setaAlbum(album);
                audioModel.setaArtist(artist);
                audioModel.setaPath(path);

                Log.e("Name :" + name, " Album :" + album);
                Log.e("Path :" + path, " Artist :" + artist);

                tempAudioList.add(audioModel);
            }
            c.close();
        }

        return tempAudioList;
    }

若要读取特定文件夹中的文件，请使用以下查询（在查询中写入目标文件夹名称）

Cursor c = context.getContentResolver().query(uri,
                                          projection, 
                                          MediaStore.Audio.Media.DATA + " like ? ", 
                                          new String[]{"%yourFolderName%"}, // yourFolderName 
                                          null);

如果您想要装置上的所有档案，请使用此查询：

Cursor c = context.getContentResolver().query(uri,
                                          projection, 
                                          null, 
                                          null, 
                                          null);

不要忘记添加存储权限。

试试这个

String path;
File sdCardRoot = Environment.getExternalStorageDirectory();
File dir = new File(sdCardRoot.getAbsolutePath() + "/yourDirectory/");

if (dir.exists()) {

    if (dir.listFiles() != null) {
        for (File f : dir.listFiles()) {
            if (f.isFile())
                path = f.getName();

            if (path.contains(".mp3")) {
                yourArrayList.add(path);

            }
        }
    }
}

此功能将为您提供设备存储中所有音频文件路径的列表

public ArrayList<String> getAllMusic(){
    Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
    String[] projection = {MediaStore.Audio.AudioColumns.DATA};
    ArrayList<String> songs_path = new ArrayList<>();
    Cursor c = context.getContentResolver().query(uri, projection, null,null,null);

    if (c != null) {
        while (c.moveToNext()) {

            String path = c.getString(0);
            songs_path.add(path);
        }
        c.close();
    }

    return songs_path;
}

ArrayList<String> allSongs = getAllMusic();

File song = new File(allSongs.get(0));