java - DocumentBuilderFactory#newInstance() 如何成为抽象工厂模式的一个例子？

Question

什么是抽象工厂模式:-

它提供了一种顶级工厂封装一组单独工厂的方式，这些工厂进一步能够创建相关产品系列没有指定他们的具体类。

根据 Examples of GoF Design Patterns in Java's core libraries下面被引用为抽象模式的例子

javax.xml.parsers.DocumentBuilderFactory#newInstance()

但我不确定它为什么会在这里遵循抽象工厂模式。

DocumentBuilderFactory 是否被认为是内部的顶级工厂包含单个工厂，即 DocumentBuilderFactory#newInstance()，它能够在不指定具体类的情况下创建相关产品系列(因为它只返回 DocumentBuilderFactory 而不是任何特定的实现) .这是正确的吗？

Answer 1

引用

什么是工厂模式？

工厂方法模式(又名工厂模式)是一种创建型模式。创建模式通过隐藏对象的创建方式来抽象对象实例化过程，并使系统独立于对象创建过程。

抽象工厂模式是比工厂方法模式高一级的抽象，这意味着它返回工厂类。

抽象工厂模式示例

常量

public interface Const {
    public static final int SHAPE_CIRCLE =1;
    public static final int SHAPE_SQUARE =2;
    public static final int SHAPE_HEXAGON =3;
}

形状工厂

public abstract class ShapeFactory {
    public abstract Shape getShape(int shapeId);
}

除了 SimpleShapeFactory 我们还创建了一个新的:

复杂形状工厂

public class ComplexShapeFactory extends ShapeFactory {
    public Shape getShape(int shapeTypeId){
        Shape shape = null;
        if(shapeTypeId == Const.SHAPE_HEXAGON) {
            shape = new Hexagon();//complex shape
        }
        else{
            // drop an error
        };
        return shape;
    }
}

现在让我们在抽象工厂创建，它返回 ShapeFactory 的一种类型:

ShapeFactoryType

public class ShapeFactoryType {
    public static final int TYPE_SIMPLE = 1;
    public static final int TYPE_COMPLEX = 2;

    public ShapeFactory getShapeFactory(int type) {
        ShapeFactory sf = null;
        if(type == TYPE_SIMPLE) {
            sf = new SimpleShapeFactory();
        }
        else if (type == TYPE_COMPLEX) {
            sf = new ComplexShapeFactory();
        }
        else throw new BadShapeFactoryException("No factory!!");
        return sf;
    }
}

现在主要调用:

      ShapeFactoryType abFac = new ShapeFactoryType();

    ShapeFactory factory = null;
    Shape s = null;
    //returns a ShapeFactory but whether it is a
    //SimpleShapeFactory or a ComplexShapeFactory is not known to the caller.
    factory = abFac.getShapeFactory(1);//returns SimpleShapeFactory
    //returns a Shape but whether it is a Circle or a Pentagon is
    //not known to the caller.
    s = factory.getShape(2); //returns square.
    s.draw(); //draws a square
    //returns a ShapeFactory but whether it is a
    //SimpleShapeFactory or a ComplexShapeFactory is not
    //known to the caller.
    factory = abFac.getShapeFactory(2);
    //returns a Shape but whether it is a Circle or a Pentagon is
    //not known to the caller.
    s = factory.getShape(3); //returns a pentagon.
    s.draw(); //draws a pentagon

来自 DocumentBuilderFactory

DocumentBuilderFactory 类似于示例中的 ShapeFactoryType。

newInstance(String factoryClassName,ClassLoader classLoader) 返回基于 factoryClassName 的 DocumentBuilderFactory 的新实例(在我的例子中我使用了 abFac.getShapeFactory(1); 和 abFac.getShapeFactory(2);)。