Decorator概述

Decorator - 图1

与其他模式区别

装饰器模式和代理模式看上去编程方式非常非常相似，它们有时候还可以称为包装模式，因此你会在一些代码中看到Wrapper这样的命名。代理模式中被包装的对象往往不希望或者不方便直接使用，依此代理类起到了隐藏被代理对象的访问，代理模式更在意对外层包装类的调用。在装饰器模式中，每个组件只提供部分功能，组件经常以一种链式嵌套的方式动态的组合在一起，装饰器模式并不在意是否要隐藏另一个被装饰的对象，而是在意多个组件合成后提供的整体功能。

玩具代码案例 - 咖啡调味

被装饰的类型

ICoffee

  1. package online.javabook.gof.structural.patterns4.decorator.coffee.api;
  3. public interface ICoffee {
  4.     String getCup();
  5. }

DecoratorCoffee

  1. package online.javabook.gof.structural.patterns4.decorator.coffee.api;
  3. public class DecoratorCoffee implements ICoffee {
  5.     private ICoffee coffee;
  7.     public DecoratorCoffee(ICoffee coffee) {
  8.         this.coffee = coffee;
  9.     }
  11.     public DecoratorCoffee() {
  13.     }
  15.     @Override
  16.     public String getCup() {
  17.         if(coffee!=null) {
  18.             return coffee.getCup();
  19.         }
  20.         else{
  21.             return "";
  22.         }
  23.     }
  24. }

装饰器角色

SimpleCoffee

  1. package online.javabook.gof.structural.patterns4.decorator.coffee.impl;
  3. import online.javabook.gof.structural.patterns4.decorator.coffee.api.DecoratorCoffee;
  4. import online.javabook.gof.structural.patterns4.decorator.coffee.api.ICoffee;
  6. public class SimpleCoffee extends DecoratorCoffee {
  8.     public SimpleCoffee() {
  9.         super();
  10.     }
  12.     public SimpleCoffee(ICoffee coffee) {
  13.         super(coffee);
  14.     }
  16.     @Override
  17.     public String getCup() {
  18.         return super.getCup() + " + " + "Coffee";
  19.     }
  20. }

IceCoffee

  1. package online.javabook.gof.structural.patterns4.decorator.coffee.impl;
  3. import online.javabook.gof.structural.patterns4.decorator.coffee.api.DecoratorCoffee;
  4. import online.javabook.gof.structural.patterns4.decorator.coffee.api.ICoffee;
  6. public class IceCoffee extends DecoratorCoffee {
  8.     public IceCoffee() {
  9.         super();
  10.     }
  12.     public IceCoffee(ICoffee coffee) {
  13.         super(coffee);
  14.     }
  16.     @Override
  17.     public String getCup() {
  18.         return super.getCup() + " + " + "Ice";
  19.     }
  20. }

MilkCoffee

  1. package online.javabook.gof.structural.patterns4.decorator.coffee.impl;
  3. import online.javabook.gof.structural.patterns4.decorator.coffee.api.DecoratorCoffee;
  4. import online.javabook.gof.structural.patterns4.decorator.coffee.api.ICoffee;
  6. public class MilkCoffee extends DecoratorCoffee {
  8.     public MilkCoffee() {
  9.         super();
  10.     }
  12.     public MilkCoffee(ICoffee coffee) {
  13.         super(coffee);
  14.     }
  16.     @Override
  17.     public String getCup() {
  18.         return super.getCup() + " + " + "Milk";
  19.     }
  20. }

SaltCoffee

  1. package online.javabook.gof.structural.patterns4.decorator.coffee.impl;
  3. import online.javabook.gof.structural.patterns4.decorator.coffee.api.DecoratorCoffee;
  4. import online.javabook.gof.structural.patterns4.decorator.coffee.api.ICoffee;
  6. public class SaltCoffee extends DecoratorCoffee {
  8.     public SaltCoffee() {
  9.         super();
  10.     }
  12.     public SaltCoffee(ICoffee coffee) {
  13.         super(coffee);
  14.     }
  16.     @Override
  17.     public String getCup() {
  18.         return super.getCup() + " + " + "Salt";
  19.     }
  20. }

SugarCoffee

  1. package online.javabook.gof.structural.patterns4.decorator.coffee.impl;
  3. import online.javabook.gof.structural.patterns4.decorator.coffee.api.DecoratorCoffee;
  4. import online.javabook.gof.structural.patterns4.decorator.coffee.api.ICoffee;
  6. public class SugarCoffee extends DecoratorCoffee {
  8.     public SugarCoffee() {
  9.         super();
  10.     }
  12.     public SugarCoffee(ICoffee coffee) {
  13.         super(coffee);
  14.     }
  16.     @Override
  17.     public String getCup() {
  18.         return super.getCup() + " + " + "Sugar";
  19.     }
  20. }

不基于装饰器模式的实现

代码逻辑相互叠加

Main

  1. package org.gof.structural.patterns4.decorator.app.bad;
  3. import online.javabook.gof.structural.patterns4.decorator.coffee.impl.MilkCoffee;
  4. import online.javabook.gof.structural.patterns4.decorator.coffee.impl.SaltCoffee;
  5. import online.javabook.gof.structural.patterns4.decorator.coffee.impl.SimpleCoffee;
  6. import online.javabook.gof.structural.patterns4.decorator.coffee.impl.SugarCoffee;
  8. public class Main {
  9.     public static void main(String[] args) {
  11.         String consumer = "consumer1";
  12.         if (consumer.equals("consumer1")) {
  13.             String coffee =
  14.                     new SimpleCoffee().getCup() +
  15.                             new SugarCoffee().getCup() +
  16.                             new MilkCoffee().getCup() +
  17.                             new SaltCoffee().getCup();
  18.             System.out.println(coffee);
  20.         } else if (consumer.equals("consumer2")) {
  21.             String coffee =
  22.                     new SaltCoffee().getCup() +
  23.                             new SaltCoffee().getCup() +
  24.                             new SimpleCoffee().getCup() +
  25.                             new SugarCoffee().getCup();
  26.             System.out.println(coffee);
  28.         } else if (consumer.equals("consumer3")) {
  29.             String coffee =
  30.                     new SimpleCoffee().getCup() +
  31.                             new SugarCoffee().getCup() +
  32.                             new SugarCoffee().getCup() +
  33.                             new SaltCoffee().getCup();
  34.             System.out.println(coffee);
  35.         }
  36.     }
  37. }

Console

  1. Simple +  Sugar +  Milk +  Salt +

基于装饰器模式的实现

代码逻辑通过装饰器相互装饰

Main

  1. package online.javabook.gof.structural.patterns4.decorator.app.good;
  3. import online.javabook.gof.structural.patterns4.decorator.coffee.api.ICoffee;
  4. import online.javabook.gof.structural.patterns4.decorator.coffee.impl.*;
  6. public class Main {
  7.     public static void main(String[] args) {
  9.         String consumer = "consumer1";
  10.         if (consumer.equals("consumer1")) {
  11.             // coffee + sugar + milk + salt
  12.             ICoffee coffee = new SaltCoffee(new MilkCoffee( new SugarCoffee( new SimpleCoffee())));
  13.             System.out.println(coffee.getCup());
  15.         } else if (consumer.equals("consumer2")) {
  16.             // coffee + ice + salt + milk
  17.             ICoffee coffee = new MilkCoffee(new SaltCoffee( new IceCoffee( new SimpleCoffee())));
  18.             System.out.println(coffee.getCup());
  20.         } else if (consumer.equals("consumer3")) {
  22.             // coffee + sugar + sugar + milk
  23.             ICoffee coffee = new MilkCoffee(new SugarCoffee( new SugarCoffee( new SimpleCoffee())));
  24.             System.out.println(coffee.getCup());
  25.         }
  26.     }
  27. }

Console

 + Coffee + Sugar + Milk + Salt