code: @Override
      public WxResp send(WxOutMsg out) {
          if (out.getFromUserName() == null)
              out.setFromUserName(openid);
          String str = Wxs.asJson(out);
          if (Wxs.DEV_MODE)
              log.debug("api out msg>\n" + str);
          return call("/message/custom/send", METHOD.POST, str);
      }
docs: 基本API