apollo-adminservice/src/main/java/com/ctrip/framework/apollo/adminservice/controller/AppNamespaceController.java/AppNamespaceController/create
class AppNamespaceController:  @PostMapping("/apps/{appId}/appnamespaces")
  public AppNamespaceDTO create(@RequestBody AppNamespaceDTO appNamespace,
                                @RequestParam(defaultValue = "false") boolean silentCreation) {

    AppNamespace entity = BeanUtils.transform(AppNamespace.class, appNamespace);
    AppNamespace managedEntity = appNamespaceService.findOne(entity.getAppId(), entity.getName());

    if (managedEntity == null) {
      if (StringUtils.isEmpty(entity.getFormat())){
        entity.setFormat(ConfigFileFormat.Properties.getValue());
      }

      entity = appNamespaceService.createAppNamespace(entity);
    } else if (silentCreation) {
      appNamespaceService.createNamespaceForAppNamespaceInAllCluster(appNamespace.getAppId(), appNamespace.getName(),
          appNamespace.getDataChangeCreatedBy());

      entity = managedEntity;
    } else {
      throw new BadRequestException("app namespaces already exist.");
    }

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