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场景：对现有方法或类的增强，与代理模式不同的是，代理模式一般增强的是与原有的功能不相关的功能，比如流量统计

结构图

基于继承的装饰器模式

（1）定义接口

/*** 策略模式：不同类型选择不同的实现策略* */
public interface AbstractStrategy {/*** 模版模式：不同策略实现同一接口的共性部分（公共方法）* */default void commentMeth(){System.out.println("模版方法");}void handle(Object object);
}

（2）被装饰者 

public class AchieveOneStrategy implements AbstractStrategy{@Overridepublic void handle(Object obj) {System.out.println(obj + "hello world!");}
}

（3）抽象的装饰者

public abstract class Decoration implements AbstractStrategy {AbstractStrategy abstractStrategy;public Decoration(AbstractStrategy abstractStrategy){this.abstractStrategy = abstractStrategy;}public void handle(Object object) {abstractStrategy.handle(object);}}

（4）具体的装饰者

public class CustomDecoration extends Decoration{public CustomDecoration(AbstractStrategy abstractStrategy){super(abstractStrategy);}@Overridepublic void handle(Object object) {before();abstractStrategy.handle(object);after();}public void before(){System.out.println("ConcreteDecorator前置操作....");}/*** 具体组件动作执行后的装饰** @author zdp* @date   2022/9/3 17:58*/public void after(){System.out.println("ConcreteDecorator后置操作....");}}

（5）测试

public class TestOne {public static void main(String[] args) throws InterruptedException {AchieveOneStrategy achieveOneStrategy = new AchieveOneStrategy();CustomDecoration customDecoration = new CustomDecoration(achieveOneStrategy);customDecoration.handle("tom");}
}

 

实用举例：线程安全的List装饰器

public class SynchronizedCollections {static <T> List<T> synchronizedList(List<T> list){return new SynchronizedList<>(list);}static class SynchronizedList<T> implements List<T> {List<T> list;final Object obj  = new Object();public SynchronizedList(List<T> list){this.list = list;}@Overridepublic boolean add(T t) {synchronized (obj){return list.add(t);}}@Overridepublic T get(int index) {synchronized (obj) {return list.get(index);}}......}
}