code: public static synchronized List<Media> getByExtension(String extension, Media folder)
      {
          Check.notNull(extension);
          Check.notNull(folder);
  
          if (!loader.isPresent())
          {
              return getFilesByExtension(folder, extension);
          }
  
          final File jar = getJarResources();
          final String prefix = getJarResourcesPrefix();
          final String fullPath = Medias.create(prefix, folder.getPath()).getPath();
          final int prefixLength = prefix.length() + 1;
  
          return getByExtension(jar, fullPath, prefixLength, extension);
      }
docs: Get all media by extension found in the direct path (does not search in sub folders).
  
  @param extension The extension without dot; eg: png (must not be <code>null</code>).
  @param folder The folder to search in (must not be <code>null</code>).
  @return The medias found.
  @throws LionEngineException If invalid parameters.