apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/api/AdminServiceAPI.java/AdminServiceAPI/findNamespaceByCluster
class AdminServiceAPI:    public List<NamespaceDTO> findNamespaceByCluster(String appId, Env env, String clusterName) {
      NamespaceDTO[] namespaceDTOs = restTemplate.get(env, "apps/{appId}/clusters/{clusterName}/namespaces",
          NamespaceDTO[].class, appId,
          clusterName);
      return Arrays.asList(namespaceDTOs);
    }