code: @Override
      protected File getFileForLastModifiedCheck() throws IOException {
          URL url = getURL();
          if (ResourceUtils.isJarURL(url)) {
              URL actualUrl = ResourceUtils.extractArchiveURL(url);
              return ResourceUtils.getFile(actualUrl, "Jar URL");
          } else {
              return getFile();
          }
      }
docs: This implementation determines the underlying File
  (or jar file, in case of a resource in a jar/zip).