code: private boolean isZip(JarEntry entry) throws IOException {
          try (InputStream entryInputStream = sourceFatJar.getInputStream(entry)) {
              try (ZipInputStream zipInputStream = new ZipInputStream(entryInputStream)) {
                  ZipEntry ze = zipInputStream.getNextEntry();
                  if (ze == null) {
                      return false;
                  }
                  return true;
              }
          }
      }
docs: Check whether the jar entry is a zip, regardless of the extension.
  
  @param entry
  @return true or false telling if the jar entry is a valid zip
  @throws IOException