/**
  * 再帰的にフォルダIDを取得
  *
  */
 static function get_recursive_folder_id_array($folder_id_array)
 {
     $ret_folder_id_array = $folder_id_array;
     foreach ($folder_id_array as $folder_id) {
         $sub_folder_id_array = ACSGenericFolder::get_sub_folder_id_array($folder_id);
         if (count($sub_folder_id_array)) {
             // サブフォルダがあるとき
             $ret_folder_id_array = array_merge($ret_folder_id_array, ACSGenericFolder::get_recursive_folder_id_array($sub_folder_id_array));
         }
     }
     return $ret_folder_id_array;
 }