code: public static String getDefaultAddress(Configuration conf) {
      URI uri = FileSystem.getDefaultUri(conf);
      String authority = uri.getAuthority();
      if (authority == null) {
        throw new IllegalArgumentException(String.format(
            "Invalid URI for NameNode address (check %s): %s has no authority.",
            FileSystem.FS_DEFAULT_NAME_KEY, uri.toString()));
      }
      return authority;
    }
docs: Returns the fs.default name from the configuration as a string for znode name retrieval
  without a DNS lookup.
  @param conf
  @return