public function get($key) {
        $filename = $this->generateFileLocation($key);
        if (file_exists($filename) && is_readable($filename)) {
            $cache = unserialize(file_get_contents($filename));
            if ($cache['expires'] > time()) {
                return $cache['content'];
            } else {
                unlink($filename);
            }
        }
        return null;
    }