动态属性商品订单生成：建造者模式应用详解

这种情况可以使用建造者模式。建造者模式可以根据不同的属性组合来构建不同的对象，符合商品动态组合属性的需求。具体实现可以定义商品建造者类，根据不同的属性组合来构建商品对象，同时也可以定义订单建造者类，根据商品对象以及购买用户的属性来构建订单对象。例如：

public class Product {
    private BigDecimal price;
    private String level;
    private String pool;

    private Product() {}

    // Builder Class
    public static class Builder {
        private BigDecimal price;
        private String level;
        private String pool;

        public Builder setPrice(BigDecimal price) {
            this.price = price;
            return this;
        }

        public Builder setLevel(String level) {
            this.level = level;
            return this;
        }

        public Builder setPool(String pool) {
            this.pool = pool;
            return this;
        }

        public Product build() {
            Product product = new Product();
            product.price = this.price;
            product.level = this.level;
            product.pool = this.pool;
            return product;
        }
    }

    // getters
}

public class Order {
    private Product product;
    private String user;
    private String time;

    private Order() {}

    // Builder Class
    public static class Builder {
        private Product product;
        private String user;
        private String time;

        public Builder setProduct(Product product) {
            this.product = product;
            return this;
        }

        public Builder setUser(String user) {
            this.user = user;
            return this;
        }

        public Builder setTime(String time) {
            this.time = time;
            return this;
        }

        public Order build() {
            Order order = new Order();
            order.product = this.product;
            order.user = this.user;
            order.time = this.time;
            return order;
        }
    }

    // getters
}

然后可以根据不同的属性组合来构建商品和订单：

// 新用户购买普通商品
Product product1 = new Product.Builder()
    .setPrice(new BigDecimal('100'))
    .setLevel('普通')
    .setPool('A')
    .build();
Order order1 = new Order.Builder()
    .setProduct(product1)
    .setUser('新用户')
    .setTime('2022/01/01')
    .build();

// 老用户购买高档商品
Product product2 = new Product.Builder()
    .setPrice(new BigDecimal('1000'))
    .setLevel('高档')
    .setPool('B')
    .build();
Order order2 = new Order.Builder()
    .setProduct(product2)
    .setUser('老用户')
    .setTime('2022/01/01')
    .build();

// 首次购买用户购买普通商品并赠送额外商品
Product product3 = new Product.Builder()
    .setPrice(new BigDecimal('200'))
    .setLevel('普通')
    .setPool('C')
    .build();
Product extraProduct = new Product.Builder()
    .setPrice(new BigDecimal('50'))
    .setLevel('普通')
    .setPool('D')
    .build();
Order order3 = new Order.Builder()
    .setProduct(product3)
    .setUser('首次购买用户')
    .setTime('2022/01/01')
    .build();
order3.setExtraProduct(extraProduct);