PHP file cache content saving format example analysis, _PHP tutorial

<&#63;php
class Cache_Driver {
  //定义缓存的路径
  protected $_cache_path;
  //根据$config中的cache_path值获取路径信息
  public function Cache_Driver($config) {
    if (is_array($config) && isset($config['cache_path'])) {
      $this->_cache_path = $config['cache_path'];
    } else {
      $this->_cache_path = realpath(dirname(__FILE__) . "/") . "/cache/";
    }
  }
  //判断key值对应的文件是否存在，如果存在，读取value值，value以序列化存储
  public function get($id) {
    if (!file_exists($this->_cache_path . $id)) {
      return FALSE;
    }
    $data = @file_get_contents($this->_cache_path . $id);
    $data = unserialize($data);
    if (!is_array($data) || !isset($data['time']) || !isset($data['ttl'])) {
      return FALSE;
    }
    if ($data['ttl'] > 0 && time() > $data['time'] + $data['ttl']) {
      @unlink($this->_cache_path . $id);
      return FALSE;
    }
    return $data['data'];
  }
  //设置缓存信息，根据key值，生成相应的缓存文件
  public function set($id, $data, $ttl = 60) {
    $contents = array(
      'time' => time() ,
      'ttl' => $ttl,
      'data' => $data
    );
    if (@file_put_contents($this->_cache_path . $id, serialize($contents))) {
      @chmod($this->_cache_path . $id, 0777);
      return TRUE;
    }
    return FALSE;
  }
  //根据key值，删除缓存文件
  public function delete($id) {
    return @unlink($this->_cache_path . $id);
  }
  public function clean() {
    $dh = @opendir($this->_cache_path);
    if (!$dh) return FALSE;
    while ($file = @readdir($dh)) {
      if ($file == "." || $file == "..") continue;
      $path = $this->_cache_path . "/" . $file;
      if (is_file($path)) @unlink($path);
    }
    @closedir($dh);
    return TRUE;
  }
}