code: public static String decode(String str) {
      if (str != null) {
        try {
          return URLDecoder.decode(str, UTF_8.name());
        } catch (UnsupportedEncodingException e) {
          throw new RuntimeException("JVM must support UTF-8", e);
        }
      }
      return null;
    }
docs: Decode a URL encoded string, e.g. from {@code "%2F"} to {@code "/"}.