apollo-client/src/main/java/com/ctrip/framework/apollo/internals/RemoteConfigLongPollService.java/RemoteConfigLongPollService/assembleNotifications
class RemoteConfigLongPollService:  String assembleNotifications(Map<String, Long> notificationsMap) {
    List<ApolloConfigNotification> notifications = Lists.newArrayList();
    for (Map.Entry<String, Long> entry : notificationsMap.entrySet()) {
      ApolloConfigNotification notification = new ApolloConfigNotification(entry.getKey(), entry.getValue());
      notifications.add(notification);
    }
    return GSON.toJson(notifications);
  }