下面是使用AspectJ实现的工厂方法模式UML图

抽象方面FactoryMethodProtocol很简单只定义了抽象pointcut createMethod用于捕捉特定应用的创建方法（也可以省略）。

FactoryMethodProtocol抽象方面

public abstract aspect FactoryMethodProtocol {
abstract pointcut createMethod();}

FactoryMethodImpl.java

public aspect FactoryMethodImpl extends FactroyMethodProtocol{

public Fruit FruitGardener.factory(){//为创建接口定义工厂方法

return null;

}

//Inter-type声明具体创建类并实现创建接口

declare parents : AppleGardener implements FruitGardener;

declare parents : GrapeGardener implements FruitGardener;

//指定createMethod捕捉FruitGardener及其子类的创建方法

pointcut createMethod() : call(Fruit FruitGardener+.factory());

Fruit around(FruitGardener gardener) : target(gardener) && createMethod(){

return chooseGardener(gardener);//工厂方法返回抽象产品。

}

private Fruit chooseGardener(FruitGardener gardener){

if(gardener instanceof AppleGardener){

return new Apple();

}

else if(gardener instanceof GrapeGardener){

return new Grape();

}

else{

throw new RuntimeException("No such kind of fruit");

}

}

//声明编译时错误：当客户直接使用new创建具体产品时发生。

//目的：强制程序完全按照工厂方法的形式创建产品。

//可选为声明警告 declare warning : [pointcut] : [warn msg]

declare error : !(within(FruitGardener+) && !createMethod())

&&!within(FactoryMethodImpl) && call(Fruit+.new(..))

: "You can only create fruits through the method factory provided by FruitGardener and its subclass";
}

三个空的创建对象声明，其创建逻辑在FactoryMethodImpl方面中定义

public interface FruitGardener {}

public class GrapeGardener {}

public class AppleGardener {}

Fruit.java抽象产品类

public abstract class Fruit {

public abstract void grow();

public abstract void harvest();

public abstract void plant();

}

Apple.java产品类

public class Apple extends Fruit{

public void grow(){

System.out.println("Apple is growing...");

}

public void harvest(){

System.out.println("Apple has been harvested");

}

public void plant(){

System.out.println("Apple has been planted");

}

}

Grape.java产品类

public class Grape extends Fruit{

public void grow(){

System.out.println("Grape is growing...");

}

public void harvest(){

System.out.println("Grape has been harvested");

}

public void plant(){

System.out.println("Grape has been planted");

}

}

Demo.java测试代码

public class Demo {
public static void main(String[] args) {
FruitGardener gardener=new AppleGardener();

Fruit fruit=gardener.factory();//创建Apple

fruit.grow();

fruit.harvest();

fruit.plant();

gardener=new GrapeGardener();

fruit=gardener.factory();//创建Grape

fruit.grow();

fruit.harvest();

fruit.plant();

//new Apple();new Grape();//产生编译错误，不能直接生成产品

}
}

测试代码使用苹果和葡萄园丁分别创建了苹果和葡萄，其运行结果如下

Apple is growing...

Apple has been harvested.

Apple has been planted.

Grape is growing..

Grape has been harvested.

grape has been planted.

有一点值得注意，如果在Demo中加入new Apple()或new Grape()等直接创建产品的语句，则ajc编译器会根据在FactoryMethodImpl方面中声明的错误而无法编译成功，并会得到如下输出:

D:\JavaDev\jbuider\AOPFactoryMethod\src\aopfactorymethod\Demo.java 26 You can only create fruits through the method factory provided by FruitGardener and its subclass 1 error.

至此，我已经使用AspectJ完全实现了一个使用工厂方法模式设计的农场园丁的例子。本系列之四将介绍如何用AspectJ实现抽象工厂模式。