设计模式简述（三）工厂模式

描述

工厂模式用以封装复杂的实例初始化过程，供外部统一调用

简单工厂（静态工厂）

如果对象创建逻辑简单且一致，可以使用简单工厂。传入想要生成的实例类型

public class HumanFactory {public static <T> T getInstance(Class<T> c) {try {return (T) Class.forName(c.getName()).getDeclaredConstructor().newInstance();} catch (Exception e) {throw new RuntimeException("生成对象异常", e);}}
}

工厂方法模式

多种类型产品初始化逻辑不一致时，可以采用不同工厂实例来初始化对应类型的产品
由于每种产品定义了对应的工厂类，因此工厂方法不需要类型参数就非常明确需要创建的实例

• 声明工厂抽象定义

public abstract class AbstractProductFactory {public abstract Product createProduct();
}

• 声明产品抽象定义

public interface Product {String getName();default void description() {System.out.println("产品名称：" + getName());}
}

• 定义具体产品

public class Apple implements Product {@Overridepublic String getName() {return "苹果";}
}public class Banana implements Product {@Overridepublic String getName() {return "香蕉";}
}

• 定义产品对应的工厂

public class AppleFactory extends AbstractProductFactory {public Product createProduct() {// 苹果其他初始化逻辑return new Apple();}
}public class BananaFactory extends AbstractProductFactory {public Product createProduct() {// 香蕉其他初始化逻辑return new Banana();}
}

• 使用

public static void main(String[] args) {AbstractProductFactory appleFactory = new AppleFactory();Product product = appleFactory.createProduct();product.description();AbstractProductFactory bananaFactory = new BananaFactory();Product banana = bananaFactory.createProduct();banana.description();
}

抽象工厂

以上工厂方法，一个产品就需要一个工厂类。
如果产品本身就有一些共通的地方，我们可以将产品划分到同一个工厂的不同产品线，这些产品的生产可以共用一些资源。

比如，我的产品都分为大、中、小三种分类。分别进行不同的加工

• 声明抽象水果

public interface Fruit {String getName();String getSize();default void description() {System.out.println("产品名称：" + getSize() + getName());}
}

• 声明具体水果

public class BigApple implements Fruit {@Overridepublic String getName() {return "苹果";}@Overridepublic String getSize() {return "大号";}
}public class MiddleApple implements Fruit {@Overridepublic String getName() {return "苹果";}@Overridepublic String getSize() {return "中号";}
}public class SmallApple implements Fruit {@Overridepublic String getName() {return "苹果";}@Overridepublic String getSize() {return "小号";}
}

public class BigBanana implements Fruit {@Overridepublic String getName() {return "香蕉";}@Overridepublic String getSize() {return "大号";}
}public class MiddleBanana implements Fruit {@Overridepublic String getName() {return "香蕉";}@Overridepublic String getSize() {return "中号";}
}public class SmallBanana implements Fruit {@Overridepublic String getName() {return "香蕉";}@Overridepublic String getSize() {return "小号";}
}

• 声明抽象工厂

public abstract class AbstractFruitFactory {abstract Fruit bigFruit();abstract Fruit middleFruit();abstract Fruit smallFruit();
}

• 定义具体工厂

public class AppleFruitFactory extends AbstractFruitFactory{@OverrideFruit bigFruit() {return new BigApple();}@OverrideFruit middleFruit() {return new MiddleApple();}@OverrideFruit smallFruit() {return new SmallApple();}
}

public class BananaFruitFactory extends AbstractFruitFactory {@OverrideFruit bigFruit() {return new BigBanana();}@OverrideFruit middleFruit() {return new MiddleBanana();}@OverrideFruit smallFruit() {return new SmallBanana();}
}

增加工厂管理类

当抽象工厂的子类扩展时，调用方需要和各个子类工厂交互，在一定程度上违反了迪米特法则。
我们可以将工厂子类交由工厂管理类进行管理，调用方只需要和这个管理类交互即可

public final class FruitFactoryManager {private static Map<String, AbstractFruitFactory> register = new HashMap<>();static {register.put("apple", new AppleFruitFactory());register.put("banana", new BananaFruitFactory());}public static AbstractFruitFactory getFactory(String factoryCode) {return register.get(factoryCode);}
}

使用

public class Sample {public static void main(String[] args) {AbstractFruitFactory appleFactory = new AppleFruitFactory();Fruit smallApple = appleFactory.smallFruit();smallApple.description();Fruit middleApple = appleFactory.middleFruit();middleApple.description();Fruit bigApple = appleFactory.bigFruit();bigApple.description();AbstractFruitFactory bananaFactory = new BananaFruitFactory();Fruit smallBanana = bananaFactory.smallFruit();smallBanana.description();Fruit middleBanana = bananaFactory.middleFruit();middleBanana.description();Fruit bigBanana = bananaFactory.bigFruit();bigBanana.description();}
}