code: public static InputStream getResourceAsStream(String fileName) throws FileNotFoundException {
      String localPath = UI_DIR + fileName;
      String altLocalPath = INTERNAL_BUILD_UI_DIR + fileName;
      InputStream in = StaticContentHandler.class.getResourceAsStream(localPath);
      if (in == null) {
        in = StaticContentHandler.class.getResourceAsStream(altLocalPath);
      }
      if (in == null) {
        throw new FileNotFoundException(localPath + " <or> " + altLocalPath);
      }
      return in;
    }
docs: Visible for testing