重学 Java 设计模式：实战策略模式「模拟多种营销类型优惠券，折扣金额计算策略场景」

itstack-demo-design-20-01
└── src
    └── main
        └── java
            └── org.itstack.demo.design
                └── CouponDiscountService.java

/**
 * 博客：https://bugstack.cn - 沉淀、分享、成长，让自己和他人都能有所收获！
 * 公众号：bugstack虫洞栈
 * Create by 小傅哥(fustack) @2020
 * 优惠券折扣计算接口
 * <p>
 * 优惠券类型；
 * 1. 直减券
 * 2. 满减券
 * 3. 折扣券
 * 4. n元购
 */
public class CouponDiscountService {
    public double discountAmount(int type, double typeContent, double skuPrice, double typeExt) {
        // 1. 直减券
        if (1 == type) {
            return skuPrice - typeContent;
        }
        // 2. 满减券
        if (2 == type) {
            if (skuPrice < typeExt) return skuPrice;
            return skuPrice - typeContent;
        }
        // 3. 折扣券
        if (3 == type) {
            return skuPrice * typeContent;
        }
        // 4. n元购
        if (4 == type) {
            return typeContent;
        }
        return 0D;
    }
}

itstack-demo-design-20-02
└── src
    └── main
        └── java
            └── org.itstack.demo.design
                ├── event
                │    └── MJCouponDiscount.java
                │    └── NYGCouponDiscount.java
                │    └── ZJCouponDiscount.java
                │    └── ZKCouponDiscount.java
                ├── Context.java
                └── ICouponDiscount.java

public interface ICouponDiscount<T> {
    /**
     * 优惠券金额计算
     * @param couponInfo 券折扣信息；直减、满减、折扣、N元购
     * @param skuPrice   sku金额
     * @return           优惠后金额
     */
    BigDecimal discountAmount(T couponInfo, BigDecimal skuPrice);
}

public class MJCouponDiscount implements ICouponDiscount<Map<String,String>>  {
    /**
     * 满减计算
     * 1. 判断满足x元后-n元，否则不减
     * 2. 最低支付金额1元
     */
    public BigDecimal discountAmount(Map<String,String> couponInfo, BigDecimal skuPrice) {
        String x = couponInfo.get("x");
        String o = couponInfo.get("n");
        // 小于商品金额条件的，直接返回商品原价
        if (skuPrice.compareTo(new BigDecimal(x)) < 0) return skuPrice;
        // 减去优惠金额判断
        BigDecimal discountAmount = skuPrice.subtract(new BigDecimal(o));
        if (discountAmount.compareTo(BigDecimal.ZERO) < 1) return BigDecimal.ONE;
        return discountAmount;
    }
}

public class ZJCouponDiscount implements ICouponDiscount<Double>  {
    /**
     * 直减计算
     * 1. 使用商品价格减去优惠价格
     * 2. 最低支付金额1元
     */
    public BigDecimal discountAmount(Double couponInfo, BigDecimal skuPrice) {
        BigDecimal discountAmount = skuPrice.subtract(new BigDecimal(couponInfo));
        if (discountAmount.compareTo(BigDecimal.ZERO) < 1) return BigDecimal.ONE;
        return discountAmount;
    }
}

public class ZKCouponDiscount implements ICouponDiscount<Double> {
    /**
     * 折扣计算
     * 1. 使用商品价格乘以折扣比例，为最后支付金额
     * 2. 保留两位小数
     * 3. 最低支付金额1元
     */
    public BigDecimal discountAmount(Double couponInfo, BigDecimal skuPrice) {
        BigDecimal discountAmount = skuPrice.multiply(new BigDecimal(couponInfo)).setScale(2, BigDecimal.ROUND_HALF_UP);
        if (discountAmount.compareTo(BigDecimal.ZERO) < 1) return BigDecimal.ONE;
        return discountAmount;
    }
}

public class NYGCouponDiscount implements ICouponDiscount<Double> {
    /**
     * n元购购买
     * 1. 无论原价多少钱都固定金额购买
     */
    public BigDecimal discountAmount(Double couponInfo, BigDecimal skuPrice) {
        return new BigDecimal(couponInfo);
    }
}

public class Context<T> {
    private ICouponDiscount<T> couponDiscount;
    public Context(ICouponDiscount<T> couponDiscount) {
        this.couponDiscount = couponDiscount;
    }
    public BigDecimal discountAmount(T couponInfo, BigDecimal skuPrice) {
        return couponDiscount.discountAmount(couponInfo, skuPrice);
    }
}

@Test
public void test_zj() {
    // 直减；100-10，商品100元
    Context<Double> context = new Context<Double>(new ZJCouponDiscount());
    BigDecimal discountAmount = context.discountAmount(10D, new BigDecimal(100));
    logger.info("测试结果：直减优惠后金额 {}", discountAmount);
}

15:43:22.035 [main] INFO  org.itstack.demo.design.test.ApiTest - 测试结果：直减优惠后金额 90
Process finished with exit code 0

@Test
public void test_mj() {
    // 满100减10，商品100元
    Context<Map<String,String>> context = new Context<Map<String,String>>(new MJCouponDiscount());
    Map<String,String> mapReq = new HashMap<String, String>();
    mapReq.put("x","100");
    mapReq.put("n","10");
    BigDecimal discountAmount = context.discountAmount(mapReq, new BigDecimal(100));
    logger.info("测试结果：满减优惠后金额 {}", discountAmount);
}

15:43:42.695 [main] INFO  org.itstack.demo.design.test.ApiTest - 测试结果：满减优惠后金额 90
Process finished with exit code 0

@Test
public void test_zk() {
    // 折扣9折，商品100元
    Context<Double> context = new Context<Double>(new ZKCouponDiscount());
    BigDecimal discountAmount = context.discountAmount(0.9D, new BigDecimal(100));
    logger.info("测试结果：折扣9折后金额 {}", discountAmount);
}

15:44:05.602 [main] INFO  org.itstack.demo.design.test.ApiTest - 测试结果：折扣9折后金额 90.00
Process finished with exit code 0

@Test
public void test_nyg() {
    // n元购；100-10，商品100元
    Context<Double> context = new Context<Double>(new NYGCouponDiscount());
    BigDecimal discountAmount = context.discountAmount(90D, new BigDecimal(100));
    logger.info("测试结果：n元购优惠后金额 {}", discountAmount);

15:44:24.700 [main] INFO  org.itstack.demo.design.test.ApiTest - 测试结果：n元购优惠后金额 90
Process finished with exit code 0