apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/controller/NamespaceController.java/NamespaceController/findAppNamespace
class NamespaceController:  @GetMapping("/apps/{appId}/appnamespaces/{namespaceName:.+}")
  public AppNamespaceDTO findAppNamespace(@PathVariable String appId, @PathVariable String namespaceName) {
    AppNamespace appNamespace = appNamespaceService.findByAppIdAndName(appId, namespaceName);

    if (appNamespace == null) {
      throw new BadRequestException(
          String.format("AppNamespace not exists. AppId = %s, NamespaceName = %s", appId, namespaceName));
    }

    return BeanUtils.transform(AppNamespaceDTO.class, appNamespace);
  }