callmez\wechat\sdk\components\BaseWechat::getAccessToken PHP Method

    public function getAccessToken($force = false)
    {
        $time = time();
        // 为了更精确控制.取当前时间计算
        if ($this->_accessToken === null || $this->_accessToken['expire'] < $time || $force) {
            $result = $this->_accessToken === null && !$force ? $this->getCache('access_token', false) : false;
            if ($result === false) {
                if (!($result = $this->requestAccessToken())) {
                    throw new HttpException(500, 'Fail to get access_token from wechat server.');
                }
                $result['expire'] = $time + $result['expires_in'];
                $this->trigger(self::EVENT_AFTER_ACCESS_TOKEN_UPDATE, new Event(['data' => $result]));
                $this->setCache('access_token', $result, $result['expires_in']);
            }
            $this->setAccessToken($result);
        }
        return $this->_accessToken['access_token'];
    }