fix(mall): 修复优惠券金额分配计算精度问题

Administrator

2026-08-03 493881e31bbb9bb6abf9be43b37a63760c8cbf6f

 src/main/java/cc/mrbird/febs/mall/service/impl/ApiMallOrderInfoServiceImpl.java

@@ -13,10 +13,7 @@
import cc.mrbird.febs.mall.entity.*;
import cc.mrbird.febs.mall.mapper.*;
import cc.mrbird.febs.mall.service.*;
import cc.mrbird.febs.mall.vo.ApiLeaderListVo;
import cc.mrbird.febs.mall.vo.OrderDetailVo;
import cc.mrbird.febs.mall.vo.OrderListVo;
import cc.mrbird.febs.mall.vo.OrderRefundVo;
import cc.mrbird.febs.mall.vo.*;
import cc.mrbird.febs.pay.model.BrandWCPayRequestData;
import cc.mrbird.febs.pay.model.OrderStateDto;
import cc.mrbird.febs.pay.service.IPayService;
@@ -219,11 +216,13 @@
                    //是否使用优惠卷
                    if(ObjectUtil.isNotEmpty(addOrderDto.getMemberCouponId())){
                        Long memberCouponId = addOrderDto.getMemberCouponId();
                        BigDecimal skuCouponAmount = couponAmountMap.get(item.getSkuId());//使用折扣卷后的应该支付的钱
                        if(skuCouponAmount.compareTo(BigDecimal.ZERO) > 0){
                            amount = skuCouponAmount;
                        if(ObjectUtil.isNotEmpty(couponAmountMap.get(item.getSkuId()))){
                            BigDecimal skuCouponAmount = couponAmountMap.get(item.getSkuId());//使用折扣卷后的应该支付的钱
                            if(skuCouponAmount.compareTo(BigDecimal.ZERO) > 0){
                                amount = skuCouponAmount;
                            }
                            orderItem.setMemberCouponId(memberCouponId);
                        }
                        orderItem.setMemberCouponId(memberCouponId);
                    }
                    orderItem.setAmount(amount);
                    orderItem.setCnt(item.getCnt());
@@ -345,25 +344,48 @@
            return couponAmountMap;
        }
        HashMap<Long,BigDecimal> skuMapPercent = new HashMap<>();//每个订单详情的ID和amount的map
        Integer type = mallGoodsCoupon.getType();

        // 计算总减免金额（满减类型需要先算满减次数）
        BigDecimal totalDiscount;
        if (MallGoodsCoupon.TYPE_TWO == type) {
            BigDecimal divideTime = totalAmount.divide(costAmount, 0, BigDecimal.ROUND_DOWN);//累计减免次数
            totalDiscount = divideTime.multiply(realAmount);//实际总减免金额
        } else {
            totalDiscount = realAmount;
        }

        // 记录每个SKU分配的减免金额，以及SKU金额最大的商品（用于修正精度损失）
        BigDecimal allocatedDiscount = BigDecimal.ZERO;
        Long maxAmountSkuId = null;
        BigDecimal maxAmount = BigDecimal.ZERO;

        for (Map.Entry<Long,BigDecimal> entry : skuMap.entrySet()) {
            Long keySkuId = entry.getKey();
            BigDecimal valueSkuAmount = entry.getValue();
            BigDecimal divide = valueSkuAmount.divide(totalAmount, 4, BigDecimal.ROUND_DOWN);//每个商品占符合满减的总额的比例
            skuMapPercent.put(keySkuId,divide);
            Integer type = mallGoodsCoupon.getType();
            if(MallGoodsCoupon.TYPE_ONE == type){
                BigDecimal bigDecimal = realAmount.multiply(divide).setScale(2, BigDecimal.ROUND_DOWN);//每个SKU的减免金额(比例*减免金额)
                BigDecimal skuRealAmount = valueSkuAmount.subtract(bigDecimal.compareTo(BigDecimal.ZERO) > 0 ? bigDecimal : BigDecimal.ZERO);//实际支付金额
                couponAmountMap.put(keySkuId,skuRealAmount);
            }
            if(MallGoodsCoupon.TYPE_TWO == type){
                BigDecimal divideTime = totalAmount.divide(costAmount, 0, BigDecimal.ROUND_DOWN);//累计减免次数
                BigDecimal multiply = divideTime.multiply(realAmount);//实际减免金额
                BigDecimal bigDecimal = multiply.multiply(divide).setScale(2, BigDecimal.ROUND_DOWN);//每个SKU的减免金额(比例*实际减免金额)
                BigDecimal skuRealAmount = valueSkuAmount.subtract(bigDecimal.compareTo(BigDecimal.ZERO) > 0 ? bigDecimal : BigDecimal.ZERO);//实际支付金额
                couponAmountMap.put(keySkuId,skuRealAmount);

            // 直接用 (总折扣 × 商品金额) / 总金额 计算，避免比例中间舍入导致精度丢失
            BigDecimal itemDiscount = totalDiscount.multiply(valueSkuAmount).divide(totalAmount, 0, BigDecimal.ROUND_DOWN);//每个SKU的减免金额
            BigDecimal skuRealAmount = valueSkuAmount.subtract(itemDiscount.compareTo(BigDecimal.ZERO) > 0 ? itemDiscount : BigDecimal.ZERO);//实际支付金额
            couponAmountMap.put(keySkuId, skuRealAmount);
            allocatedDiscount = allocatedDiscount.add(itemDiscount);

            // 记录金额最大的SKU，用于后续修正精度损失
            if (valueSkuAmount.compareTo(maxAmount) > 0) {
                maxAmount = valueSkuAmount;
                maxAmountSkuId = keySkuId;
            }
        }

        // 修正精度损失：ROUND_DOWN导致分配的减免金额可能小于总减免金额，将差额补到金额最大的商品上
        BigDecimal diff = totalDiscount.subtract(allocatedDiscount);
        if (diff.compareTo(BigDecimal.ZERO) > 0 && maxAmountSkuId != null) {
            BigDecimal oldAmount = couponAmountMap.get(maxAmountSkuId);
            couponAmountMap.put(maxAmountSkuId, oldAmount.subtract(diff));
        }

        return couponAmountMap;
    }

@@ -612,6 +634,12 @@
//        if (orderInfo == null || AppContants.DEL_FLAG_Y == orderInfo.getDelFlag()) {
        if (ObjectUtil.isNull(orderInfo)) {
            throw new FebsException("订单不存在");
        }
        List<MallOrderItem> items = orderInfo.getItems();
        if(CollUtil.isNotEmpty(items)){
            for(MallOrderItem mallOrderItem : items){
                mallOrderItem.setItemAmount(mallOrderItemMapper.selectById(mallOrderItem.getId()).getAmount());
            }
        }

        OrderDetailVo orderDetailVo = MallOrderInfoConversion.INSTANCE.entityToDetailVo(orderInfo);
@@ -1035,4 +1063,19 @@
        return new FebsResponse().success();
    }

    @Override
    public FebsResponse chooseCoupon(ApiChooseCouponDto chooseCouponDto) {
        Map<Long, BigDecimal> couponAmountMap = getCouponAmountMap(chooseCouponDto.getMemberCouponId(), chooseCouponDto.getItems());
        ArrayList<ApiCouponAmountMapVo> objects = new ArrayList<>();
        for (Map.Entry<Long,BigDecimal> entry : couponAmountMap.entrySet()) {
            Long keySkuId = entry.getKey();
            BigDecimal valueSkuAmount = entry.getValue();
            ApiCouponAmountMapVo apiCouponAmountMapVo = new ApiCouponAmountMapVo();
            apiCouponAmountMapVo.setId(keySkuId);
            apiCouponAmountMapVo.setAmount(valueSkuAmount);
            objects.add(apiCouponAmountMapVo);
        }
        return new FebsResponse().success().data(objects);
    }

}