code: private static String getExtension(String fileName) {
          // play it safe and get rid of any fragment id
          // that might be there
          int length = fileName.length();
  
          int newEnd = fileName.lastIndexOf('#');
          if (newEnd == -1) {
              newEnd = length;
          }
          int i = fileName.lastIndexOf('.', newEnd);
          if (i != -1) {
              return fileName.substring(i + 1, newEnd);
          } else {
              // no extension, no content type
              return null;
          }
      }
docs: Get extension of file, without fragment id