public static @Nullable String getExtensionFromMimeType(String mimeType) {
    String result = sMimeTypeToExtensionMap.get(mimeType);
    if (result != null) {
      return result;
    }
    return sMimeTypeMap.getExtensionFromMimeType(mimeType);
  }
Wrapper around the system's {@link MimeTypeMap} that also handles types it doesn't support.
fbcore/src/main/java/com/facebook/common/media/MimeTypeMapWrapper.java