第一种是通过ContentResolver获取

    public static String getMimeType(Context context,File file,@NonNull String authority){
        Uri uri;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            uri = FileProvider.getUriForFile(context, authority, file);
        } else {
            uri = Uri.fromFile(file);
        }

        ContentResolver resolver = context.getContentResolver();
        return resolver.getType(uri);
    }

另一种是通过URLConnection获取

    public static String getMimeType(File file){
        FileNameMap fileNameMap = URLConnection.getFileNameMap();
        String type = fileNameMap.getContentTypeFor(file.getName());
        return type;
    }