code: public final Map<String, Set<String>> getMimeExtensionMap() throws OSException {
          initializeMimeExtensionArrays();
          return Collections.unmodifiableMap(mimeExtension);
      }
docs: Creates a map with MIME types as keys pointing on sets of associated file
  extensions.
  
  @return Map of MIME types pointing on sets of file extensions
  @throws OSException