/**
  * get user object by userName
  * @param  string $userName
  * @return object user object
  */
 public static function newFromName($userName)
 {
     $cache = self::getUserCache();
     $u = $cache->get(User::IdFromName($userName));
     if ($u) {
         return $u;
     }
     $u = new HuijiUser();
     $u->mUser = User::NewFromName($userName);
     if ($u->mUser == null) {
         return null;
     }
     return $u;
 }