UnifiedOrderReqData reqData = new UnifiedOrderReqData.UnifiedOrderReqDataBuilder("appid", "mch_id",
                "body", "out_trade_no", 1, 
                "spbill_create_ip", "notify_url", "JSAPI")
                .setOpenid("openid").build();
Map<String, Object> resultMap = WxPayApi.UnifiedOrder(reqData);

String responseXml = new PayNotifyTemplate(requestXml).execute(new PaySuccessCallBack() {
    @Override
    public void onSuccess(PayNotifyData payNotifyData) {
      //进行业务处理

      //如果处理失败，抛出异常
    }
});