外观模式

1.定义：又叫门面模式，提供了一个统一的接口，用来访问子系统中的一群接口；
　　　　外观模式定义了一个高层接口，让子系统更容易使用。

2.类型：结构型

3.适用场景：子系统越来越复杂，增加外观模式提供简单调用接口；
　　构建多层系统结构，利用外观对象作为每层的入口，简化层间调用。

4.优点：简化了调用过程，无需了解深入子系统，防止带来风险；
　　　   减少系统依赖、松散耦合；更好的划分访问层次；
　　　   符合迪米特法则，即最少知道原则。

5.缺点：增加子系统、扩展子系统行为容易引入风险；不符合开闭原则。

6.相关设计模式：中介者模式、单例模式、抽象工厂模式。

7.实例目录package

8.实例UML类图

9.代码

package com.geely.design.pattern.structural.facade;

public class PointsGift {
    private String name;

    public PointsGift(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

package com.geely.design.pattern.structural.facade;

public class QualifyService {
    public boolean isAvailable(PointsGift pointsGift){
        System.out.println("校验" + pointsGift.getName() + "积分资格通过，库存通过");
        return true;
    }
}

package com.geely.design.pattern.structural.facade;

public class PointsPaymentService {
    public boolean pay(PointsGift pointsGift){
        //扣减积分
        System.out.println("支付"+pointsGift.getName()+" 积分成功");
        return true;
    }
}

package com.geely.design.pattern.structural.facade;

public class ShippingService {
    public String shipGift(PointsGift pointsGift){
        //物流系统的对接逻辑
        System.out.println(pointsGift.getName() + "进入物流系统");
        String shippingOrderNo = "666";
        return shippingOrderNo;
    }
}

package com.geely.design.pattern.structural.facade;

public class GiftExchangeService {
    private QualifyService qualifyService;
    private PointsPaymentService pointsPaymentService;
    private ShippingService shippingService;

    /*public void setQualifyService(QualifyService qualifyService) {
        this.qualifyService = qualifyService;
    }

    public void setPointsPaymentService(PointsPaymentService pointsPaymentService) {
        this.pointsPaymentService = pointsPaymentService;
    }

    public void setShippingService(ShippingService shippingService) {
        this.shippingService = shippingService;
    }*/

    public void giftExchange(PointsGift pointsGift){
        if(qualifyService.isAvailable(pointsGift)){
            if(pointsPaymentService.pay(pointsGift)){
                String shippingOrderNo = shippingService.shipGift(pointsGift);
                System.out.println("物流系统下单成功，订单号是："+shippingOrderNo);
            }
        }
    }
}

package com.geely.design.pattern.structural.facade;

public class Test {
    public static void main(String[] args) {
        PointsGift pointsGift = new PointsGift("T恤");
        GiftExchangeService giftExchangeService = new GiftExchangeService();
        /*giftExchangeService.setPointsPaymentService(new PointsPaymentService());
        giftExchangeService.setQualifyService(new QualifyService());
        giftExchangeService.setShippingService(new ShippingService());*/

        giftExchangeService.giftExchange(pointsGift);
    }
}