apollo-configservice/src/main/java/com/ctrip/framework/apollo/configservice/service/AppNamespaceServiceWithCache.java/AppNamespaceServiceWithCache/findPublicNamespaceByName
class AppNamespaceServiceWithCache:  public AppNamespace findPublicNamespaceByName(String namespaceName) {
    Preconditions.checkArgument(!Strings.isNullOrEmpty(namespaceName), "namespaceName must not be empty");
    return publicAppNamespaceCache.get(namespaceName);
  }