public static function getUserByID($userid)
 {
     $user = CacheManager::getUserCache($userid);
     $userVO = new UserVO();
     if (isset($user) && !is_null($user)) {
         $userVO->id = $user->id;
         $userVO->nickname = $user->nickname;
         $userVO->user_pic_url = $user->user_photo_url;
     }
     return $userVO;
 }