Events中无法写文件缓存？

public static function set($name, $value, $expire = 0)
    {
        if (empty($name)) {
            return false;
        }
        if (empty($value)) {
            return false;
        }
        $filename    = self::filename($name);
        $data        = ;
        $json_encode = json_encode($data);
        file_put_contents($filename, $json_encode);
    }

    private static function filename($filename)
    {
        $name = './json/';
        return $name . md5($filename) . '.json';
    }