apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/service/AppNamespaceService.java/AppNamespaceService/checkPublicAppNamespaceGlobalUniqueness
class AppNamespaceService:  private void checkPublicAppNamespaceGlobalUniqueness(AppNamespace appNamespace) {
    AppNamespace publicAppNamespace = findPublicAppNamespace(appNamespace.getName());
    if (publicAppNamespace != null) {
      throw new BadRequestException("AppNamespace " + appNamespace.getName() + " already exists as public namespace in appId: " + publicAppNamespace.getAppId() + "!");
    }
  }