public  function loadConfig( $file ){
		if( file_exists( $file ) ){
			$config = include $file;
			$driver = $config['driver'];
			if( $driver == 'file'){
				$session = new \Wudimei\Session\File($config);
			}
			$this->session = $session;
		}
		else{
			throw new \Exception('sesstion config file "' . $file . '" does not exists');
		}
		

	}