自动更新微信access token

class class_weixin
{
var $appid = APPID;
var $appsecret = APPSECRET;

//构造函数，获取Access Token
public function __construct($appid = NULL, $appsecret = NULL)
{
if($appid && $appsecret){
$this->appid = $appid;
$this->appsecret = $appsecret;
}

//1. 数据库形式
/*
DROP TABLE IF EXISTS `wx_token`;
CREATE TABLE IF NOT EXISTS `wx_token` (
`id` int(1) NOT NULL,
`type` varchar(20) NOT NULL,
`expire` varchar(16) NOT NULL,
`value` varchar(600) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

INSERT INTO `wx_token` (`id`, `type`, `expire`, `value`) VALUES
(1, 'access_token', '1425534992', 't3oyW9fRnOWKQHQhZXoEH-pgThhjmnCqTVpaLyUD'),
(2, 'jsapi_ticket', '', '');
*/
$con = mysql_connect(MYSQLHOST.':'.MYSQLPORT, MYSQLUSER, MYSQLPASSWORD);
mysql_select_db(MYSQLDATABASE, $con);
$result = mysql_query("SELECT * FROM `wx_token` WHERE `type` = 'access_token'");
while($row = mysql_fetch_array($result))
{
$this->access_token = $row['value'];
$this->expires_time = $row['expire'];
break;
}
if (time() > ($this->expires_time + 3600)){
$url = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=".$this->appid."&secret=".$this->appsecret;
$res = $this->http_request($url);
$result = json_decode($res, true);
$this->access_token = $result["access_token"];
$this->expires_time = time();
mysql_query("UPDATE `wx_token` SET `expire` = '$this->expires_time', `value` = '$this->access_token' WHERE `type` = 'access_token';");
}

//2. 缓存形式
if (isset($_SERVER['HTTP_APPNAME'])){        //SAE环境，需要开通memcache
$mem = memcache_init();
}else {                                        //本地环境，需已安装memcache
$mem = new Memcache;
$mem->connect('localhost', 11211) or die ("Could not connect");
}
$this->access_token = $mem->get($this->appid);
if (!isset($this->access_token) || empty($this->access_token)){
$url = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=".$this->appid."&secret=".$this->appsecret;
$res = $this->http_request($url);
$result = json_decode($res, true);
$this->access_token = $result["access_token"];
$mem->set($this->appid, $this->access_token, 0, 3600);
}

//3. 本地写入
$res = file_get_contents('access_token.json');
$result = json_decode($res, true);
$this->expires_time = $result["expires_time"];
$this->access_token = $result["access_token"];

if (time() > ($this->expires_time + 3600)){
$url = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=".$this->appid."&secret=".$this->appsecret;
$res = $this->http_request($url);
$result = json_decode($res, true);
$this->access_token = $result["access_token"];
$this->expires_time = time();
file_put_contents('access_token.json', '{"access_token": "'.$this->access_token.'", "expires_time": '.$this->expires_time.'}');
}

//4. 实时拉取
$url = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=".$this->appid."&secret=".$this->appsecret;
$res = $this->http_request($url);
$result = json_decode($res, true);
$this->access_token = $result["access_token"];
$this->expires_time = time();
}