apollo-configservice/src/main/java/com/ctrip/framework/apollo/configservice/service/AppNamespaceServiceWithCache.java/AppNamespaceServiceWithCache/findPublicNamespacesByNames
class AppNamespaceServiceWithCache:  public List<AppNamespace> findPublicNamespacesByNames(Set<String> namespaceNames) {
    if (namespaceNames == null || namespaceNames.isEmpty()) {
      return Collections.emptyList();
    }

    List<AppNamespace> result = Lists.newArrayList();
    for (String namespaceName : namespaceNames) {
      AppNamespace appNamespace = publicAppNamespaceCache.get(namespaceName);
      if (appNamespace != null) {
        result.add(appNamespace);
      }
    }
    return result;
  }