SpringBoot 模板模式实现优惠券逻辑的示例代码

public interface RuleTemplate {
    // 计算优惠券
    ShoppingCart calculate(ShoppingCart settlement);
}

public ShoppingCart calculate(ShoppingCart order) {
    // 获取订单总价
    Long orderTotalAmount = getTotalPrice(order.getProducts());
    // 获取以shopId为维度的总价统计
    Map<Long, Long> sumAmount = getTotalPriceGroupByShop(order.getProducts());
    CouponTemplateInfo template = order.getCouponInfos().get(0).getTemplate();
    // 最低消费限制
    Long threshold = template.getRule().getDiscount().getThreshold();
    // 优惠金额或者打折比例
    Long quota = template.getRule().getDiscount().getQuota();
    // 如果优惠券未指定shopId，则shopTotalAmount=orderTotalAmount
    // 如果指定了shopId，则shopTotalAmount=对应门店下商品总价
    Long shopId = template.getShopId();
    Long shopTotalAmount = (shopId == null) ? orderTotalAmount : sumAmount.get(shopId);
    // 如果不符合优惠券使用标准, 则直接按原价走，不使用优惠券
    if (shopTotalAmount == null || shopTotalAmount < threshold) {
        log.debug("Totals of amount not meet");
        order.setCost(orderTotalAmount);
        order.setCouponInfos(Collections.emptyList());
        return order;
    }
    // 子类中实现calculateNewPrice计算新的价格
    Long newCost = calculateNewPrice(orderTotalAmount, shopTotalAmount, quota);
    if (newCost < minCost()) {
        newCost = minCost();
    }
    order.setCost(newCost);
    log.debug("original price={}, new price={}", orderTotalAmount, newCost);
    return order;
}

@Slf4j
@Component
public class MoneyOffTemplate extends AbstractRuleTemplate implements RuleTemplate {
    @Override
    protected Long calculateNewPrice(Long totalAmount, Long shopAmount, Long quota) {
        // benefitAmount是扣减的价格
        // 如果当前门店的商品总价<quota，那么最多只能扣减shopAmount的钱数
        Long benefitAmount = shopAmount < quota ? shopAmount : quota;
        return totalAmount - benefitAmount;
    }    
}

@Component
@Slf4j
public class CouponTemplateFactory {
    @Autowired
    private MoneyOffTemplate moneyOffTemplate;
    @Autowired
    private DiscountTemplate discountTemplate;
    @Autowired
    private RandomReductionTemplate randomReductionTemplate;
    @Autowired
    private LonelyNightTemplate lonelyNightTemplate;
    @Autowired
    private DummyTemplate dummyTemplate;
    @Autowired
    private AntiPauTemplate antiPauTemplate;
    public RuleTemplate getTemplate(ShoppingCart order) {
        // 不使用优惠券
        if (CollectionUtils.isEmpty(order.getCouponInfos())) {
            // dummy模板直接返回原价，不进行优惠计算
            return dummyTemplate;
        }
        // 获取优惠券的类别
        // 目前每个订单只支持单张优惠券
        CouponTemplateInfo template = order.getCouponInfos().get(0).getTemplate();
        CouponType category = CouponType.convert(template.getType());
        switch (category) {
            // 订单满减券
            case MONEY_OFF:
                return moneyOffTemplate;
            // 随机立减券
            case RANDOM_DISCOUNT:
                return randomReductionTemplate;
            // 午夜下单优惠翻倍
            case LONELY_NIGHT_MONEY_OFF:
                return lonelyNightTemplate;
            // 打折券
            case DISCOUNT:
                return discountTemplate;
            case ANTI_PUA:
                return antiPauTemplate;
            // 未知类型的券模板
            default:
                return dummyTemplate;
        }
    }
}

    @Autowired
    private CouponTemplateFactory couponProcessorFactory;
    // 优惠券结算
    // 这里通过Factory类决定使用哪个底层Rule，底层规则对上层透明
    @Override
    public ShoppingCart calculateOrderPrice(@RequestBody ShoppingCart cart) {
        log.info("calculate order price: {}", JSON.toJSONString(cart));
        RuleTemplate ruleTemplate = couponProcessorFactory.getTemplate(cart);
        return ruleTemplate.calculate(cart);
    }