Java Android应用程序Mp3文件mimetype解析为空

我正在尝试获取mp3的mimetype存储在下载中。问题是mimetype总是返回null。我不知道为什么。请注意，将扩展名设置为小写（.mp3）没有什么区别

String filePath = "/storage/emulated/0/Download/song.MP3";

File file = new File(filePath);
Uri uri2 = Uri.fromFile(file);

//will display /storage/emulated/0/Download/song.MP3
Log.d("file type as string",file.toString());

//will display file:///storage/emulated/0/Download/song.MP3
Log.d("uri type as string",uri2.toString());


ContentResolver cR = getApplicationContext().getContentResolver();
String mime = cR.getType(uri2);

//mime is null always displays
if(mime == null){
    Log.d("result", "mime is null");
} else{
    Log.d("mime", mime);
}

String extension = android.webkit.MimeTypeMap.getFileExtensionFromUrl(filePath);
String mimetype = android.webkit.MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);


System.out.println("extension:" +extension); //displays MP3
System.out.println("mimetype:" + mimetype); //displays null

---

检查下面的代码。您将了解为什么没有获得所需的输出

    String type = null;
    String extension = "mp3";

    type = android.webkit.MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);

    Log.d(TAG,"mime type1 "+type);

    extension = "MP3";

    type = android.webkit.MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);

    Log.d(TAG,"mime type2 "+type);

如果不能在小写文件扩展的基础上产生任何差异，请考虑使用

File filesDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
    File mov = new File(filesDir,"song.mp3");

并使用文件的绝对路径而不是硬编码路径来构造uri