public function write($key, $content, $timestamp = null)
    {
        if (!isset($this->cacheDirectory)) {
            return;
        }

        $this->loadCacheMetaData();
        $this->metaData[$key] = $timestamp;
        $this->dirty = true;

        if (!is_dir($this->cacheDirectory)) {
            mkdir($this->cacheDirectory, 0775, true);
        }
        file_put_contents($this->cacheDirectory . '/' . $key, serialize($content));
    }