关于Session入库的有关问题

class SessionDBTool {
    //MySQLDB类的对象
    private $db;

	public function __construct(){
		//设置处理器方法
		ini_set('session.save_handler', 'user');
		session_set_save_handler(
			array($this,'sess_open'),
			array($this,'sess_close'),
			array($this,'sess_read'),
			array($this,'sess_write'),
			array($this,'sess_destroy'),
			array($this,'sess_gc')
			);
		//开启session
		session_start();
	}

	public function sess_open(){
        $this->db = MySQLDB::getInstance($GLOBALS['config']['database']);
	}

	public function sess_close(){
        return true;
	}

	public function sess_read($sess_id){
        $sql = "select sess_data from it_session where sess_id = '$sess_id'";
        return (string)$this->db->fetchColumn($sql);
    }

	public function sess_write($sess_id,$sess_data){
        $expire = time();
        $sql = "insert into it_session values('$sess_id','$sess_data',$expire) on duplicate key update sess_data = '$sess_data',expire = $expire";
        return $this->db->query($sql);
	}

	public function sess_destroy($sess_id){
        $sql = "delete from it_session where sess_id = '$sess_id'";
        return $this->db->query($sql);
	}

	public function sess_gc($ttl){
        $last_time = time() - $ttl;
        $sql = "delete from it_session where expire < $last_time";
        return $this->db->query($sql);
	}
}

?>

/**
 * Created by PhpStorm.
 * User: DoubleJack
 * Date: 2015/5/13
 * Time: 23:18
 */
    class BackPlatformController extends Controller {
        /**
         * 构造函数，使其自动checklogin()
         */
        public function __construct(){
            //开启session
            $this->initSession();
            //验证是否登陆
            $this->checkLogin();

        }
        /**
         * 初始化session入库
         */
        protected function initSession(){
           new SessionDBTool;
        }

        /**
         * 验证当前用户是否登陆
         */
        protected function checkLogin(){
            //判断是否登录
            if(CONTROLLER=="admin" && (ACTION=="login" || ACTION=="signin")) {
                //不需要
            }else{
                //需要
                    if(isset($_SESSION['is_login']) && $_SESSION['is_login'] == 'YES'){
                        //载入后台的模板
                        require CURR_VIEW_DIR . 'index.html';
                 //继续执行
                }else{

                    $this->jump('index.php?p=back&c=Admin&a=login','请先登录',2);
                }
            }
        }



    }