一、Access Token

access_token是公众号的全局唯一票据，公众号调用各接口时都需使用access_token。正常情况下access_token有效期为7200秒，重复获取将导致上次获取的access_token失效。

公众号可以使用AppID和AppSecret调用本接口来获取access_token。AppID和AppSecret可在开发模式中获得（需要已经成为开发者，且帐号没有异常状态）。注意调用所有微信接口时均需使用https协议。

接口调用请求说明

http请求方式: GET

https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=APPID&secret=APPSECRET

参数说明

参数	是否必须	说明
grant_type	是	获取access_token填写client_credential
appid	是	第三方用户唯一凭证
secret	是	第三方用户唯一凭证密钥，既appsecret

返回说明

正常情况下，微信会返回下述JSON数据包给公众号：

{"access_token":"ACCESS_TOKEN","expires_in":7200}

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();

    }