code: @Override
    public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      if (req.getRequestURI().endsWith("upload")) {
        uploadCallback(req, resp);
      } else {
        resp.setStatus(HttpServletResponse.SC_NOT_FOUND);
      }
    }
docs: Url paths supported
  /api/blob/upload (POST) Default callback after a successful upload