protected synchronized void reflushAccessToken() {
        String url = String.format("%s/token?grant_type=client_credential&appid=%s&secret=%s", base, appid, appsecret);
        if (log.isDebugEnabled())
            log.debugf("ATS: reflush access_token send: %s", url);

        Response resp = Http.get(url);
        if (!resp.isOK())
            throw new IllegalArgumentException("reflushAccessToken FAIL , openid=" + openid);
        String str = resp.getContent();

        if (log.isDebugEnabled())
            log.debugf("ATS: reflush access_token done: %s", str);

        NutMap re = Json.fromJson(NutMap.class, str);
        String token = re.getString("access_token");
        int expires = re.getInt("expires_in") - 200;//微信默认超时为7200秒，此处设置稍微短一点
        accessTokenStore.save(token, expires, System.currentTimeMillis());
    }