1. 集成微信支付步骤看我得另一个博客,流程都是完整的，亲测可用

springboot集成微信jsapi支付，使用v3接口，实现获取预支付交易id_微信支付jsapiservice.prepay-CSDN博客

2. 微信退款实现，只贴实现类，refundNotifyUrl就是退款信息得回调地址，记住要和你得退款接口对应

@Override
    @Transactional(rollbackFor = Exception.class)
    public Result weixinRefund(RefundDto refundDto,BywOrder bywOrder) {
//请求对象
        CreateRequest request = new CreateRequest();
        AmountReq amountReq = new AmountReq();
        //退款金额
        amountReq.setRefund(new BigDecimal(refundDto.getRefundAmount()).longValue());
        //原订单金额
        amountReq.setTotal(bywOrder.getOrderAmount().longValue());
        //货币类型(默认人民币)
        amountReq.setCurrency("CNY");
        request.setOutRefundNo(refundDto.getOutTradeNo());
        request.setAmount(amountReq);
        request.setOutTradeNo(refundDto.getOriginOutTradeNo());
        request.setReason("订单退款");
        request.setNotifyUrl(refundNotifyUrl);
        //返回信息
        Refund refund = refundService.create(request);
        if (SUCCESS.equals(refund.getStatus().SUCCESS)) {
            refundDto.setRefundStatus(true);
            insertRefundOrder(refundDto,bywOrder);
            return Result.ok(refund, 200, "调用退款申请成功");
        } else {
            refundDto.setRefundStatus(false);
            insertRefundOrder(refundDto,bywOrder);
            return Result.error(500, "调用退款申请失败");
        }

3. 接收微信退款信息通知

    @PostMapping("/weixinRefundNotify")
    public void refund_notify(@RequestBody String body,HttpServletRequest request, HttpServletResponse response) throws Exception {
        weixinPayService.weixinRefundNotify(body,request,response);
    }





@Override
    public void weixinRefundNotify(String body, HttpServletRequest request, HttpServletResponse response) throws Exception {
        //获取报文
        //随机串
        String nonceStr = request.getHeader("Wechatpay-Nonce");
        //微信传递过来的签名
        String signature = request.getHeader("Wechatpay-Signature");
        //证书序列号（微信平台）
        String serialNo = request.getHeader("Wechatpay-Serial");
        //时间戳
        String timestamp = request.getHeader("Wechatpay-Timestamp");
        InputStream is = null;
        try {
            is = request.getInputStream();
            // 构造 RequestParam
            com.wechat.pay.java.core.notification.RequestParam requestParam = new com.wechat.pay.java.core.notification.RequestParam.Builder()
                    .serialNumber(serialNo)
                    .nonce(nonceStr)
                    .signature(signature)
                    .timestamp(timestamp)
                    .body(body)
                    .build();
            // 如果已经初始化了 RSAAutoCertificateConfig，可以直接使用  config
            // 初始化 NotificationParser
            // 验签、解密并转换成 Transaction
            RefundNotification refundNotification = notificationParser.parse(requestParam, RefundNotification.class);
            String orderNo = refundNotification.getOutTradeNo();
            //记录日志信息
            System.out.println("订单号：" + orderNo);
            if (SUCCESS.equals(refundNotification.getRefundStatus().SUCCESS)) {
                System.out.println("退款成功");
                //TODO------
                //根据自己的需求处理相应的业务逻辑,异步
                JSONObject jsonObject = JSONObject.parseObject(refundNotification.toString());
                System.out.println("微信退款回调信息：" + jsonObject);
                JSONObject resultJson = new JSONObject();
                resultJson.put("out_trade_no", jsonObject.getString("out_trade_no"));
                resultJson.put("refund_status", jsonObject.getString("refund_status"));
                //业务处理
                //通知微信回调成功
                response.getWriter().write("<xml><return_code><![CDATA[SUCCESS]]></return_code></xml>");
            } else {
                System.out.println("微信回调失败,JsapiPayController.payNotify.transaction：" + refundNotification.toString());
                //通知微信回调失败
                response.getWriter().write("<xml><return_code><![CDATA[FAIL]]></return_code></xml>");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            is.close();
        }
    }

response.getWriter().write("<xml><return_code><![CDATA[SUCCESS]]></return_code></xml>");

需要回调微信成功或失败，不然会出发微信的重试机制，可能会发多次退款回调信息