装饰模式

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decorator 模式的功能是：给一个对象添加一些额外的职责（操作），虽然此功能可以用继承实现，但装饰模式比生成子类更灵活些。

装饰的意思：就是包装一下。把另的对象包装一下。我这里只简单示例下怎么使用。

业务接口 Component：

package com.chenlb.dp.decorator;

/**
* 业务接口
*/
public interface Component {

     void operation();
}

具体业务 ConcreteComponent：

package com.chenlb.dp.decorator;

/**
* 具体业务类.
*/
public class ConcreteComponent implements Component {

     public void operation() {
         System.out.println("I'm "+this.getClass().getName());
     }

}

装饰 Decorator：

package com.chenlb.dp.decorator;

/**
* 装饰类.
*/
public class Decorator implements Component {

    private Component component;

    public Decorator(Component component) {
        this.component = component;
    }

    public void operation() {
        component.operation();
    }

}

执行前装饰 BeforeDecorator：

package com.chenlb.dp.decorator;

/**
* 在业务执行前加点额外的操作.
*/
public class BeforeDecorator extends Decorator {

     public BeforeDecorator(Component component) {
         super(component);
     }

     public void operation() {
         before();
         super.operation();
     }

     private void before() {
         System.out.println("before: I'm "+this.getClass().getName());
     }

}

执行后装饰 AfterDecorator：

package com.chenlb.dp.decorator;

/**
* 在业务执行完后添加额外的操作.
*/
public class AfterDecorator extends Decorator {

     public AfterDecorator(Component component) {
         super(component);
     }

     public void operation() {
         super.operation();
         after();
     }

     private void after() {
         System.out.println("after: I'm "+this.getClass().getName());
     }
}

运行示例 Demo：

package com.chenlb.dp.decorator;

public class Demo {

    public static void main(String[] args) {
        Component component = new ConcreteComponent();
        component.operation();
        System.out.println("----------------------------------------");
        component = new BeforeDecorator(new ConcreteComponent());
        component.operation();
        System.out.println("----------------------------------------");
        component = new AfterDecorator(new ConcreteComponent());
        component.operation();
        System.out.println("----------------------------------------");
        component = new AfterDecorator(new BeforeDecorator(new ConcreteComponent()));
        component.operation();
        System.out.println("----------------------------------------");
        component = new BeforeDecorator(new AfterDecorator(new ConcreteComponent()));
        component.operation();
    }

}