一、模式定义
在不改变原有对象的前提下（不改变ConcreteComponent情况下），给原有对象扩展功能（利用ConcreteDecorator扩展功能，在ConcreteDecorator中注入ConcreteComponent）。如下所示：
二、应用场景
扩展一个类的功能，或者给一个类添加一些附加职责
三、优点：
①、灵活改变组合；
②、符合开闭原则；
四、装饰者模式的实现方式
4.1、方式1
package decorator;public class DecoratorDesignPattern {public static void main(String[] args) {Decorator decoratorA = new ConcreteDecoratorA(new ConcreteComponent());decoratorA.operation();Decorator decoratorB = new ConcreteDecoratorB(new ConcreteDecoratorA(new ConcreteComponent()));decoratorB.operation();}
}interface Component{void operation();
}class ConcreteComponent implements Component{@Overridepublic void operation() {System.out.println("拍照...\n");}
}abstract class Decorator implements Component{Component component;public Decorator(Component component) {this.component = component;}
}class ConcreteDecoratorA extends Decorator{public ConcreteDecoratorA(Component component) {super(component);}@Overridepublic void operation() {System.out.println("添加美颜....");component.operation();}
}class ConcreteDecoratorB extends Decorator{public ConcreteDecoratorB(Component component) {super(component);}@Overridepublic void operation() {System.out.println("添加滤镜");component.operation();}
}
上面代码的运行结果如下：
4.2、方式2
package decorator;public class DecoratorPattern {public static void main(String[] args) {Circle circle = new Circle();RedShapeDecorator redCircle = new RedShapeDecorator(circle);Rectangle rectangle = new Rectangle();RedShapeDecorator redRectangle = new RedShapeDecorator(rectangle);System.out.println("Circle with normal border");circle.draw();System.out.println("\nCircle of red border");redCircle.draw();System.out.println("\nRectangle of red border");redRectangle.draw();}
}interface Shape {void draw();
}class Circle implements Shape {@Overridepublic void draw() {System.out.println("Shape：Circle");}
}class Rectangle implements Shape {@Overridepublic void draw() {System.out.println("Shape：Rectangle");}
}abstract class ShapeDecorator implements Shape {public Shape decoratedShape;public ShapeDecorator(Shape decoratorShape) {this.decoratedShape = decoratorShape;}@Overridepublic void draw() {decoratedShape.draw();}
}class RedShapeDecorator extends ShapeDecorator {public RedShapeDecorator(Shape decoratorShape) {super(decoratorShape);}@Overridepublic void draw() {decoratedShape.draw();setRedBorder(decoratedShape);}private void setRedBorder(Shape decoratedShape){System.out.println("Border Color: Red");}
}
上面代码的运行结果如下：
五、装饰者模式的应用
Java IO 库采用了装饰器模式（Decorator Pattern）和适配器模式（Adapter Pattern）的组合设计模式，其中InputStream是装饰器模式中顶层的抽象类，FilterInputStream是装饰器基类，BufferedInputStream是带有缓冲区的装饰器类，ObjectInputStream是可以读取对象的装饰器类，SequenceInputStream是可以顺序读取多个输入Stream的装饰器类，FileInputStream、ByteArrayInputStream则是被装饰的类。 这些类的UML图，如下所示：
