think\Cache::has PHP Method

    public static function has($name)
    {
        self::init();
        self::$readTimes++;
        return self::$handler->has($name);
    }

 /**
  * 读取或者设置缓存
  * @access public
  * @param string $key 缓存标识，支持变量规则 ，例如 item/:name/:id
  * @param mixed  $expire 缓存有效期
  * @return mixed
  */
 public function cache($key, $expire = null)
 {
     if ($this->isGet()) {
         if (false !== strpos($key, ':')) {
             $param = $this->param();
             foreach ($param as $item => $val) {
                 if (is_string($val) && false !== strpos($key, ':' . $item)) {
                     $key = str_replace(':' . $item, $val, $key);
                 }
             }
         } elseif ('__URL__' == $key) {
             // 当前URL地址作为缓存标识
             $key = md5($this->url());
         } elseif (strpos($key, ']')) {
             if ('[' . $this->ext() . ']' == $key) {
                 // 缓存某个后缀的请求
                 $key = md5($this->url());
             } else {
                 return;
             }
         }
         if (strtotime($this->server('HTTP_IF_MODIFIED_SINCE')) + $expire > $_SERVER['REQUEST_TIME']) {
             // 读取缓存
             $response = Response::create()->code(304);
             throw new \think\exception\HttpResponseException($response);
         } elseif (Cache::has($key)) {
             list($content, $header) = Cache::get($key);
             $response = Response::create($content)->header($header);
             throw new \think\exception\HttpResponseException($response);
         } else {
             $this->cache = [$key, $expire];
         }
     }
 }