code: public static Useragent getUserAgent(HttpServletRequest request) {
      String head = request.getHeader("USER-AGENT");
      Useragent agent = new Useragent(getIpAddr(request), Browser.parse(head), Os.parse(head));
      if (agent.getOs().equals(OsCategory.Unknown) || agent.getBrowser().equals(BrowserCategory.Unknown)) {
        logger.info("Cannot parser user agent:{}", request.getHeader("USER-AGENT"));
      }
      return agent;
    }
docs: Return {@code Useragent} of request.
  
  @param request