apollo-configservice/src/main/java/com/ctrip/framework/apollo/configservice/util/WatchKeysUtil.java/WatchKeysUtil/namespacesBelongToAppId
class WatchKeysUtil:  private Set<String> namespacesBelongToAppId(String appId, Set<String> namespaces) {
    if (ConfigConsts.NO_APPID_PLACEHOLDER.equalsIgnoreCase(appId)) {
      return Collections.emptySet();
    }
    List<AppNamespace> appNamespaces =
        appNamespaceService.findByAppIdAndNamespaces(appId, namespaces);

    if (appNamespaces == null || appNamespaces.isEmpty()) {
      return Collections.emptySet();
    }

    return appNamespaces.stream().map(AppNamespace::getName).collect(Collectors.toSet());
  }