//获取access_token
    function getAccessToken(){
        $appid = C('app_id');
        $appsecret =C('app_secret');
        $isExpires = isExpires();
        if($isExpires === false){
            //到期，获取新的
            $url = 'https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=' . $appid . '&secret=' . $appsecret;
            $res = curl($url);
            // dump($res);
            $arr = json_decode($res,true);
            if($arr && !isset($arr['errcode'])){
                $arr['time'] = time();
                file_put_contents(APP_PATH . '../access_token.json', json_encode($arr));
                return $arr['access_token'];
            }else{
                echo 'error on get access_token';die;
            }
        }else{
            return $isExpires;
        }
    }
//更新access_token
     function isExpires(){
        if(!file_exists(APP_PATH . '../access_token.json')){
            return false;
        }
        $res = file_get_contents(APP_PATH . '../access_token.json');
        $arr = json_decode($res,true);
        if($arr && time()<(intval($arr['time'])+intval($arr['expires_in']))){
            //未过期
            return $arr['access_token'];
        }else{
            return false;
        }
    }