code: public static String extractDataRoot(String publicURL, String accessURL) {
      if (publicURL != null && !publicURL.startsWith("http")) {
        return "";
      }
      String reminder = publicURL.substring(accessURL.length() + 1);
      String container = null;
      if (reminder.indexOf("/") > 0) {
        container =  reminder.substring(0, reminder.indexOf("/"));
      } else {
        container = reminder;
      }
      if (container.endsWith("/")) {
        container = container.substring(0, container.length() - 1);
      }
      return container;
    }
docs: Extracts container name from http://hostname/v1/auth_id/container/object
  
  @param publicURL public url
  @param accessURL access url
  @return container name