code: private boolean isSuccessfulResponseToUnsafeRequest(HTTPResponse resolvedResponse) {
          Status.Category category = resolvedResponse.getStatus().getCategory();
          return category == Status.Category.SUCCESS || category == Status.Category.REDIRECTION;
      }
docs: http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-22#section-6