apollo-portal/src/main/java/com/ctrip/framework/apollo/openapi/v1/controller/NamespaceController.java/NamespaceController/findNamespaces
class NamespaceController:  @GetMapping(value = "/openapi/v1/envs/{env}/apps/{appId}/clusters/{clusterName}/namespaces")
  public List<OpenNamespaceDTO> findNamespaces(@PathVariable String appId, @PathVariable String env,
                                               @PathVariable String clusterName) {
    return this.namespaceOpenApiService.getNamespaces(appId, env, clusterName);
  }