读编写高质量代码整理（十）—使用反射增加装饰模式的普遍性

1。何为装饰者模式(Decorator Pattern)？

"动态地给一个对象天剑一些额外的职责，就增加功能来说，装饰模式比生成子类更加灵活"。

2。装饰模式类图

 

3。代码如下：

书本例子：我们以卡通片《猫和老鼠》（《Tom and Jerry》）为例，看看如何包装小Jerry让它更强大。

Component接口：

/**
 * Component
 * @author decorator
 */
public interface Animal {
	public void doStuff();
}

 ConcreteComponent类：

/**
 * ConcreteComponent
 * @author decorator
 */
public class Rat implements Animal {
	public void doStuff() {
		System.out.println("Jerry play ...");
	}
}

 Decorator接口：

/**
 * Decorator
 * @author decorator
 */
public interface Feature{
	public void load();
}

 ConcreteDecorator1:

/**
 * ConcreteDecorator
 * @author decorator
 */
public class FlyFeature implements Feature {
	public void load() {
		System.out.println("增加一双翅膀...");
	}

}

 ConcreteDecorator2:

/**
 * ConcreteDecorator
 * @author decorator
 */
public class DigFeature implements Feature{
	public void load() {
		System.out.println("增加钻地能力...");
	}
}

 DecorateComponent:

public class DecorateAnimal implements Animal {

	//被包装的动物
	private Animal animal;
	//使用拿一个包装器
	private Class<? extends Feature> clz;

	public DecorateAnimal(Animal _animal,Class<? extends Feature> _clz) {
		animal = _animal;
		clz = _clz;
	}
	@Override
	public void doStuff() {
		
		InvocationHandler handler = new InvocationHandler() {
			@Override //具体包装行为
			public Object invoke(Object proxy, Method method, Object[] args)
					throws Throwable {
				Object obj = null;
				if(Modifier.isPublic(method.getModifiers())) {
					obj = method.invoke(clz.newInstance(), args);
					System.out.println(method.getName());
				
				}
				animal.doStuff();
				return obj;
			}
		};
		//当前加载类
		ClassLoader cl = this.getClass().getClassLoader();		
		//接口动态代理
		Feature proxy = (Feature) Proxy.newProxyInstance(cl,
				//clz.getInterfaces(),
				new Class[]{Feature.class},
				handler);
		
//		Class proxyClass = Proxy.getProxyClass(
//				Feature.class.getClassLoader(),
//				new Class[]{Feature.class});
//		Feature proxy = null ;
//		try {
//			 proxy=(Feature) proxyClass
//				 	.getConstructor(InvocationHandler.class)
//				 	.newInstance(new Object[]{handler});
//		} catch (Exception e) {
//			e.printStackTrace();
//		}
		proxy.load();
	}
	
	public static void main(String[] args) {
		Animal jerry = new Rat();
		jerry = new DecorateAnimal(jerry, FlyFeature.class);
		jerry = new DecorateAnimal(jerry, DigFeature.class);
		jerry.doStuff();
	}
}