public static function getWriters()
  {
    if (is_null(self::$_writers)) {
      $writers = Config::getInstance("JooS_Log")->writers;
      /* @var $writers JooS_Config */
      if (!is_null($writers)) {
        foreach ($writers->valueOf() as $name) {
          $name = ucfirst(strtolower($name));
          $className = Loader::getClassName(__NAMESPACE__ . "\\", $name);
          if (Loader::loadClass($className)) {
            $writer = new $className();
            if ($writer instanceof Log_Interface) {
              self::addWriter($writer);
            }
          }
        }
      } else {
        self::$_writers = array();
      }
    }
    return self::$_writers;
  }