一、基本概念

装饰器模式是指不必在改变原有的类和不使用继承的情况下，动态扩展一个对象的功能。

二、角色设计

角色	描述
抽象构件	是一个接口或者抽象类，定义我们最核心的对象
基础构件	抽象构件的实现，可以单独用，也可以将其进行装饰
装饰角色	一般是一个抽象类，继承自或实现抽象构件，在它的属性中有个变量指向抽象构建，这是关键
具体装饰角色	Type-C充电和Wireless充电是两个具体的装饰类，可以把基础构件进行装饰，延伸出新的功能

三、代码实现

案例一

假设一个场景，以前手机充电只有usb充电，但是目前手机多出了2种新的充电方式，Typc-C和无线充电，这就需要我们动态去扩展功能，让我们看看装饰器如何实现的。

1、首先定义一个基本的充电接口，采用usb充电

public interface Charge {
    
    public void usb();
    
}

2、实现一个普通手机去使用usb接口充电

public class PhoneCharge implements Charge{

    @Override
    public void usb() {
        System.out.println("采用usb接口充电...");
    }
    
}

3、抽象的充电装饰器

public abstract class AbstractPhoneDecorator implements Charge{

    protected final Charge charge;

    public AbstractPhoneDecorator(Charge charge){
        this.charge = charge;
    }

}

4、Type-C充电具体装饰

public class TypeCDecorator extends AbstractPhoneDecorator{


    public TypeCDecorator(Charge charge) {
        super(charge);
    }

    @Override
    public void usb() {
        super.charge.usb();
        System.out.println("采用type-c接口充电...");
    }

}

5、无线充电的具体装饰

public class WirelessDecorator extends AbstractPhoneDecorator{

    public WirelessDecorator(Charge charge) {
        super(charge);
    }

    @Override
    public void usb() {
        super.charge.usb();
        System.out.println("采用无线充电...");
    }
    
}

6、测试类

    public static void main(String[] args) {
        
        Charge charge = new PhoneCharge();
        TypeCDecorator typeCDecorator = new TypeCDecorator(charge);
        WirelessDecorator wirelessDecorator = new WirelessDecorator(typeCDecorator);
        wirelessDecorator.usb();
        
    }

7、运行结果

案例二

现在假设有一个新的场景，在我们平时网上购买一个商品可以不光使用红包抵扣，同时也有满减优惠，案例二假设一个用户在网上买了10个单价为15元的牙杯，他现在有一个20元的红包和50元的抵扣券，下面通过代码来进行简单的模拟实现。

1、创建订单实体类

import java.math.BigDecimal;

/**
 * 订单类
 * @author HTT
 */
public class Order {

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getGoodsInfo() {
        return goodsInfo;
    }

    public void setGoodsInfo(String goodsInfo) {
        this.goodsInfo = goodsInfo;
    }

    public BigDecimal getGoodsPrice() {
        return goodsPrice;
    }

    public void setGoodsPrice(BigDecimal goodsPrice) {
        this.goodsPrice = goodsPrice;
    }

    public BigDecimal getGoodsCount() {
        return goodsCount;
    }

    public void setGoodsCount(BigDecimal goodsCount) {
        this.goodsCount = goodsCount;
    }

    public Coupon getFullReduction() {
        return fullReduction;
    }

    public void setFullReduction(Coupon couponInfo) {
        this.fullReduction = couponInfo;
    }

    public Coupon getRedPacketInfo() {
        return redPacketInfo;
    }

    public void setRedPacketInfo(Coupon redPacketInfo) {
        this.redPacketInfo = redPacketInfo;
    }

    public BigDecimal getGoodsAmount() {
        return goodsAmount;
    }

    public void setGoodsAmount(BigDecimal goodsAmount) {
        this.goodsAmount = goodsAmount;
    }

    /**
     * 订单id
     */
    private String id;

    /**
     * 商品信息
     */
    private String goodsInfo;

    /**
     * 商品价格
     */
    private BigDecimal goodsPrice;

    /**
     * 商品信息
     */
    private BigDecimal goodsCount;

    /**
     * 商品总价
     */
    private BigDecimal goodsAmount;

    /**
     * 满减信息
     */
    private Coupon fullReduction;
    /**
     * 红包信息
     */
    private Coupon redPacketInfo;
}

2、创建优惠券实体类

import java.math.BigDecimal;

/**
 * 优惠信息
 * @author HTT
 */
public class Coupon {

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public BigDecimal getCouponPrice() {
        return couponPrice;
    }

    public void setCouponPrice(BigDecimal couponPrice) {
        this.couponPrice = couponPrice;
    }


    public String getCouponType() {
        return couponType;
    }

    public void setCouponType(String couponType) {
        this.couponType = couponType;
    }

    private int id;

    /**
     * 优惠金额
     */
    private BigDecimal couponPrice;

    /**
     * 优惠券类型
     */
    private String couponType;

}

3、创建一个抽象构建，是所有订单的基本需求，用于计算订单的总额

/**
 * 抽象构建 用于计算订单总金额
 * @author HTT
 */
public interface OrderDecorator {

    public BigDecimal calculateOrderPrice(Order order);
    
}

4、抽象构建的基础实现类

/**
 * 基础构建实现类 计算订单金额
 * @author HTT
 */
public class BaseOrder implements OrderDecorator{

    @Override
    public BigDecimal calculateOrderPrice(Order order) {
        return order.getGoodsPrice().multiply(order.getGoodsCount());
    }

}

5、订单的抽象装饰器

/**
 * 抽象的订单装饰器
 * @author HTT
 */
public abstract class BaseOrderDecorator implements OrderDecorator{

    private OrderDecorator orderDecorator;

    public BaseOrderDecorator(OrderDecorator orderDecorator){
        this.orderDecorator = orderDecorator;
    }

    @Override
    public BigDecimal calculateOrderPrice(Order order) {
        return orderDecorator.calculateOrderPrice(order);
    }

}

6、红包装饰器

/**
 * 红包装饰器
 * @author HTT
 */
public class RedPacketDecorator extends BaseOrderDecorator{

    public RedPacketDecorator(OrderDecorator orderDecorator) {
        super(orderDecorator);
    }

    @Override
    public BigDecimal calculateOrderPrice(Order order) {
        order.setGoodsAmount(super.calculateOrderPrice(order));
        return calculateRedPacketPrice(order);
    }

    private BigDecimal calculateRedPacketPrice(Order order){
        return order.getGoodsAmount().subtract(order.getRedPacketInfo().getCouponPrice());
    }
}

7、满减装饰器

/**
 * 满减装饰器
 * @author HTT
 */
public class FullReductionDecorator extends BaseOrderDecorator{

    public FullReductionDecorator(OrderDecorator orderDecorator) {
        super(orderDecorator);
    }

    @Override
    public BigDecimal calculateOrderPrice(Order order) {
        order.setGoodsAmount(super.calculateOrderPrice(order));
        return calculateRedPacketPrice(order);
    }

    private BigDecimal calculateRedPacketPrice(Order order){
        return order.getGoodsAmount().subtract(order.getFullReduction().getCouponPrice());
    }
}

8、测试

public static void main(String[] args) {
        //初始化红包信息
        Coupon redPacket = new Coupon();
        redPacket.setId(1);
        redPacket.setCouponType("红包");
        redPacket.setCouponPrice(new BigDecimal("20"));
        //初始化满减信息
        Coupon fullReduction = new Coupon();
        fullReduction.setId(2);
        fullReduction.setCouponType("满减");
        fullReduction.setCouponPrice(new BigDecimal("50"));

        //初始化订单信息
        Order order = new Order();
        order.setId(UUID.randomUUID().toString());
        order.setGoodsInfo("牙杯");
        order.setGoodsPrice(new BigDecimal("15"));
        order.setGoodsCount(new BigDecimal("10"));
        order.setRedPacketInfo(redPacket);
        order.setFullReduction(fullReduction);

        OrderDecorator orderDecorator = new BaseOrder();
        BaseOrderDecorator redPacketDecorator = new RedPacketDecorator(orderDecorator);
        BaseOrderDecorator fullReductionDecorator = new FullReductionDecorator(redPacketDecorator);
        System.out.println(fullReductionDecorator.calculateOrderPrice(order));

    }

9、运行结果