如何在使用Firebase Web Legacy HTTP Server协议推送的推送通知中显示图标

Question

我已在安全环境中部署了Web应用程序。我正在使用FCM HTTP服务器协议来请求FCM应用服务器以将推送通知发送到订户列表。我想在通知中显示一个图标，服务器上存在我的图标文件。我怎样才能做到这一点。请帮忙。

以下是Java中用于推送通知的代码。

private MsgDTO pushNotificationService(String[] tokenArray,
            String serverKey, SendNotificationReqType sendNotificationReqType)
            throws AppException {
        MsgDTO msgDTO = new MsgDTO();
            {
            HttpURLConnection httpcon = (HttpURLConnection) ((new URL(
                    "https://fcm.googleapis.com/fcm/send").openConnection()));
            httpcon.setDoOutput(true);
            httpcon.setRequestProperty("Content-Type", "application/json");
            httpcon.setRequestProperty(
                    "Authorization",
                    "key="+serverKey);
            httpcon.setRequestMethod("POST");
            httpcon.connect();
            LOG.debug("Connected!");

            JSONObject json = new JSONObject();

            json.put("registration_ids", tokenArray);
            JSONObject info = new JSONObject();
            info.put("title", sendNotificationReqType.getTitle()); // Notification title
            info.put("body", sendNotificationReqType.getMessage()); // Notification body
            info.put("icon","*icon url*");                                      // 
            json.put("notification", info);

            LOG.debug("pushNotification : "+json.toString());
            OutputStreamWriter wr = new OutputStreamWriter(
                    httpcon.getOutputStream());
            wr.write(json.toString());
            wr.flush();
            }

以下是客户端上的JS代码。

  messaging.onMessage(function(payload) {
    // Customize notification here
    var notificationTitle = payload.notification.title;
    var notificationOptions = {
      body: payload.notification.body,
      icon: '*icon url*'
    };

    return self.registration.showNotification(notificationTitle,
      notificationOptions);
  });