抽象工厂模式（Abstract Factory Pattern）

顾名思义，它是属于创建设计模式之一，作为工厂模式上的抽象层。抽象设计模式是比工厂模式更抽象一级的模式。

在工厂模式的例子基础之上，添加地域功能，以实现全局范围的汽车类型。UML 类图如下：

完整代码如下：

public enum Location {
     DEFAULT, USA, ASIA
}

public enum CarType {
    SMALL, SEDAN, LUXURY
}

public abstract class Car {
    public Car(CarType model, Location location){
        this.model = model;
        this.location = location;
        System.out.println("location is " + location);
    }

    protected abstract void construct();

    private CarType model = null;
    private Location location = null;

    public CarType getModel() {
        return model;
    }

    public void setModel(CarType model) {
        this.model = model;
    }

    public Location getLocation() {
        return location;
    }

    public void setLocation(Location location) {
        this.location = location;
    }

    @Override
    public String toString() {
        return "Model- "+model + " built in "+location;
    }
}

public class SmallCar extends Car {

    SmallCar(Location location) {
        super(CarType.SMALL, location);
        construct();
    }

    @Override
    protected void construct() {
        System.out.println("Building small car");
        // add accessories
    }
}

public class SedanCar extends Car {
    SedanCar(Location location) {
        super(CarType.SEDAN, location);
        construct();
    }

    @Override
    protected void construct() {
        System.out.println("Building sedan car");
        // add accessories
    }
}

public class LuxuryCar extends Car{
    public LuxuryCar(Location location)
    {
        super(CarType.LUXURY, location);
        construct();
    }

    @Override
    protected void construct() {
        System.out.println("Building luxury car");
        //add accessories
    }
}

public class USACarFactory {
    public static Car buildCar(CarType model)
    {
        Car car = null;
        switch (model)
        {
            case SMALL:
                car = new SmallCar(Location.USA);
                break;

            case SEDAN:
                car = new SedanCar(Location.USA);
                break;

            case LUXURY:
                car = new LuxuryCar(Location.USA);
                break;

            default:
                //throw some exception
                break;
        }
        return car;
    }
}

public class DefaultCarFactory {
    public static Car buildCar(CarType model)
    {
        Car car = null;
        switch (model)
        {
            case SMALL:
                car = new SmallCar(Location.DEFAULT);
                break;

            case SEDAN:
                car = new SedanCar(Location.DEFAULT);
                break;

            case LUXURY:
                car = new LuxuryCar(Location.DEFAULT);
                break;

            default:
                //throw some exception
                break;
        }
        return car;
    }
}

public class AsiaCarFactory {
    public static Car buildCar(CarType model)
    {
        Car car = null;
        switch (model)
        {
            case SMALL:
                car = new SmallCar(Location.ASIA);
                break;

            case SEDAN:
                car = new SedanCar(Location.ASIA);
                break;

            case LUXURY:
                car = new LuxuryCar(Location.ASIA);
                break;

            default:
                //throw some exception
                break;
        }
        return car;
    }
}

public class CarFactory
{
	private CarFactory() {
		//Prevent instantiation
	}

	public static Car buildCar(CarType type)
	{
		Car car = null;
		Location location = Location.ASIA; //Read location property somewhere from configuration
		//Use location specific car factory
		switch(location)
		{
			case USA:
			car = USACarFactory.buildCar(type);
			break;
			case ASIA:
			car = AsiaCarFactory.buildCar(type);
			break;
			default:
			car = DefaultCarFactory.buildCar(type);
		}
	return car;
	}
}

测试代码：

public class CarAbstractFactoryTest {

    @SuppressWarnings("deprecation")
    @Test
    public void testCarFactory() {
        Assert.assertEquals(true, CarFactory.buildCar(CarType.SMALL) instanceof Car) ;
        Assert.assertEquals(true, CarFactory.buildCar(CarType.SEDAN) instanceof Car) ;
        Assert.assertEquals(true, CarFactory.buildCar(CarType.LUXURY) instanceof Car) ;
    }
}

默认情况是亚洲，结果如下：

location is ASIA
Building small car
location is ASIA
Building sedan car
location is ASIA
Building luxury car

正如你看到的，抽象工厂模式是在工厂模式的抽象级别。如果想更深入研究，请查阅Java API:

• DocumentBuilderFactory#newInstance()
• TransformerFactory#newInstance()