Java设计模式(四)：工厂设计模式

我会带着你远行 2022-04-02 08:00 245阅读 0赞

# 1. 工厂设计模式 #

## 1.1 应用场景 ##

由于需求的变化，一个类的子类经常面临着剧烈的变化，但他却拥有比较稳定的接口。使用一种封装机制来“隔离这种易变对象的变化”，工厂方法定义一个用于创建对象的接口，让子类来确定创建哪一个具体类的对象，将对象的实例化延迟。

## 1.2 概念 ##

定义了一个创建对象的接口，但由子类决定要实例化哪个类。工厂方法把实例化操作推迟到子类。

## 1.3 Class Diagram ##

在简单工厂中，创建对象的是另一个类，而在工厂方法中，是由子类来创建对象。

下图中，Factory 有一个 doSomething() 方法，这个方法需要用到一个产品对象，这个产品对象由 factoryMethod() 方法创建,也称为“工厂方法”。该方法是抽象的，需要由子类去实现。在抽象的Factory中，任何其他实现的方法，都可能使用到这个工厂方法所制造出来的产品，但只有子类真正实现了这个工厂方法并创建产品。

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxMTI1MTgz_size_16_color_FFFFFF_t_70]

## 1.4 Implementation ##

public abstract class Pizza { 
    	String name;
    	String dough;
    	String sauce;
    	ArrayList<String> toppings = new ArrayList<String>();
     
    	void prepare() { 
    		System.out.println("Prepare " + name);
    		System.out.println("Tossing dough...");
    		System.out.println("Adding sauce...");
    		System.out.println("Adding toppings: ");
    		for (String topping : toppings) { 
    			System.out.println(" " + topping);
    		}
    	}
      
    	void bake() { 
    		System.out.println("Bake for 25 minutes at 350");
    	}
     
    	void cut() { 
    		System.out.println("Cut the pizza into diagonal slices");
    	}
      
    	void box() { 
    		System.out.println("Place pizza in official PizzaStore box");
    	}
     
    	public String getName() { 
    		return name;
    	}
    
    	public String toString() { 
    		StringBuffer display = new StringBuffer();
    		display.append("---- " + name + " ----\n");
    		display.append(dough + "\n");
    		display.append(sauce + "\n");
    		for (String topping : toppings) { 
    			display.append(topping + "\n");
    		}
    		return display.toString();
    	}
    }
    
    public abstract class PizzaStore { 
        public Pizza orderPizza(String type){ 
            Pizza pizza;
            pizza=createPizza(type);
    
            pizza.prepare();
            pizza.bake();
            pizza.cut();
            pizza.box();
    
            return pizza;
        }
    
        public abstract Pizza createPizza(String type);
    }
    
    public class NYStyleCheesePizza extends Pizza { 
    
    	public NYStyleCheesePizza() {  
    		name = "NY Style Sauce and Cheese Pizza";
    		dough = "Thin Crust Dough";
    		sauce = "Marinara Sauce";
     
    		toppings.add("Grated Reggiano Cheese");
    	}
    }
    
    public class ChicagoStyleCheesePizza extends Pizza { 
    
    	public ChicagoStyleCheesePizza() {  
    		name = "Chicago Style Deep Dish Cheese Pizza";
    		dough = "Extra Thick Crust Dough";
    		sauce = "Plum Tomato Sauce";
     
    		toppings.add("Shredded Mozzarella Cheese");
    	}
     
    	void cut() { 
    		System.out.println("Cutting the pizza into square slices");
    	}
    }
    
    public class ChicagoStylePizzaStore extends PizzaStore{ 
        @Override
        public Pizza createPizza(String type) { 
            if(type.equals("cheese"))
                return new ChicagoStyleCheesePizza();
            return null;
        }
    }
    
    public class NYStylePizzaStore extends PizzaStore{ 
        @Override
        public Pizza createPizza(String type) { 
            if(type.equals("cheese"))
                return new NYStyleCheesePizza();
            return null;
        }
    }
    
    public class PizzaTestDrive { 
        public static void main(String[] args) { 
            PizzaStore nyStylePizzaStore=new NYStylePizzaStore();
            PizzaStore chicagoStylePizzaStore=new ChicagoStylePizzaStore();
            Pizza nyStylePizza = nyStylePizzaStore.orderPizza("cheese");
            System.out.println("Ethan ordered a " + nyStylePizza.getName() + "\n");
    
            Pizza chicagoPizza = chicagoStylePizzaStore.orderPizza("cheese");
            System.out.println("Ethan ordered a " + chicagoPizza.getName() + "\n");
        }
    }

## 1.5 JDK ##

*  [java.util.Calendar][]
 *  [java.util.ResourceBundle][]
 *  [java.text.NumberFormat][]
 *  [java.nio.charset.Charset][]
 *  [java.net.URLStreamHandlerFactory][]
 *  [java.util.EnumSet][]
 *  [javax.xml.bind.JAXBContext][]

# 2. 抽象工厂方法 #

## 2.1 应用场景 ##

一系列相互依赖的对象有不同的具体实现。提供一种“封装机制”来避免客户程序和这种“多系列具体对象创建工作”的紧耦合。

## 2.2 概念 ##

提供一个接口，用于创建 相关的对象家族，而不需要明确的指定具体类。抽象工厂允许客户使用抽象的接口来创建一组相关的产品，而不需要知道或者关心实际产出的产品是什么。这样一来客户就从具体的产品中被解耦。

## 2.3 Class Diagram ##

抽象工厂模式创建的是对象家族，也就是很多对象而不是一个对象，并且这些对象是相关的，也就是说必须一起创建出来。而工厂方法模式只是用于创建一个对象，这和抽象工厂模式有很大不同。

抽象工厂模式用到了工厂方法模式来创建单一对象，AbstractFactory 中的 createProductA() 和 createProductB() 方法都是让子类来实现，这两个方法单独来看就是在创建一个对象，这符合工厂方法模式的定义。

至于创建对象的家族这一概念是在 Client 体现，Client 要通过 AbstractFactory 同时调用两个方法来创建出两个对象，在这里这两个对象就有很大的相关性，Client 需要同时创建出这两个对象。

从高层次来看，抽象工厂使用了组合，即 Cilent 组合了 AbstractFactory，而工厂方法模式使用了继承。

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxMTI1MTgz_size_16_color_FFFFFF_t_70 1]

## 2.4 Implementation ##

public interface Cheese { 
    	public String toString();
    }
    
    public interface Clams { 
    	public String toString();
    }
    
    public interface Dough { 
    	public String toString();
    }
    
    public class FreshClams implements Clams { 
    
    	public String toString() { 
    		return "Fresh Clams from Long Island Sound";
    	}
    }
    
    public class Garlic implements Veggies { 
    
    	public String toString() { 
    		return "Garlic";
    	}
    }
    
    public class MarinaraSauce implements Sauce { 
    	public String toString() { 
    		return "Marinara Sauce";
    	}
    }
    
    public class Mushroom implements Veggies { 
    
    	public String toString() { 
    		return "Mushrooms";
    	}
    }
    
    public class Onion implements Veggies { 
    
    	public String toString() { 
    		return "Onion";
    	}
    }
    
    public interface Pepperoni { 
    	public String toString();
    }
    
    public class RedPepper implements Veggies { 
    
    	public String toString() { 
    		return "Red Pepper";
    	}
    }
    
    public class ReggianoCheese implements Cheese { 
    
    	public String toString() { 
    		return "Reggiano Cheese";
    	}
    }
    
    public interface Sauce { 
    	public String toString();
    }
    
    public class SlicedPepperoni implements Pepperoni { 
    
    	public String toString() { 
    		return "Sliced Pepperoni";
    	}
    }
    
    public class ThinCrustDough implements Dough { 
    	public String toString() { 
    		return "Thin Crust Dough";
    	}
    }
    
    public interface Veggies { 
    	public String toString();
    }
    
    public interface PizzaIngredientFactory { 
        public Dough createDough();
        public Sauce createSauce();
        public Cheese createCheese();
        public Veggies[] createVeggies();
        public Pepperoni createPepperoni();
        public Clams createClams();
    }
    
    public abstract class Pizza { 
    	public String name;
    
    	public Dough dough;
    	public Sauce sauce;
    	public Veggies veggies[];
    	public Cheese cheese;
    	public Pepperoni pepperoni;
    	public Clams clam;
    
    	public abstract void prepare();
    
    	public void bake() { 
    		System.out.println("Bake for 25 minutes at 350");
    	}
    
    	public void cut() { 
    		System.out.println("Cutting the pizza into diagonal slices");
    	}
    
    	public void box() { 
    		System.out.println("Place pizza in official PizzaStore box");
    	}
    
    	public void setName(String name) { 
    		this.name = name;
    	}
    
    	public String getName() { 
    		return name;
    	}
    
    	public String toString() { 
    		StringBuffer result = new StringBuffer();
    		result.append("---- " + name + " ----\n");
    		if (dough != null) { 
    			result.append(dough);
    			result.append("\n");
    		}
    		if (sauce != null) { 
    			result.append(sauce);
    			result.append("\n");
    		}
    		if (cheese != null) { 
    			result.append(cheese);
    			result.append("\n");
    		}
    		if (veggies != null) { 
    			for (int i = 0; i < veggies.length; i++) { 
    				result.append(veggies[i]);
    				if (i < veggies.length-1) { 
    					result.append(", ");
    				}
    			}
    			result.append("\n");
    		}
    		if (clam != null) { 
    			result.append(clam);
    			result.append("\n");
    		}
    		if (pepperoni != null) { 
    			result.append(pepperoni);
    			result.append("\n");
    		}
    		return result.toString();
    	}
    }
    
    public class CheesePizza extends Pizza { 
    	PizzaIngredientFactory ingredientFactory;
     
    	public CheesePizza(PizzaIngredientFactory ingredientFactory) { 
    		this.ingredientFactory = ingredientFactory;
    	}
     
    	public void prepare() { 
    		System.out.println("Preparing " + name);
    		dough = ingredientFactory.createDough();
    		sauce = ingredientFactory.createSauce();
    		cheese = ingredientFactory.createCheese();
    	}
    }
    
    public class ClamPizza extends Pizza { 
    	PizzaIngredientFactory ingredientFactory;
     
    	public ClamPizza(PizzaIngredientFactory ingredientFactory) { 
    		this.ingredientFactory = ingredientFactory;
    	}
     
    	public void prepare() { 
    		System.out.println("Preparing " + name);
    		dough = ingredientFactory.createDough();
    		sauce = ingredientFactory.createSauce();
    		cheese = ingredientFactory.createCheese();
    		clam = ingredientFactory.createClams();
    	}
    }
    
    public class PepperoniPizza extends Pizza { 
    	PizzaIngredientFactory ingredientFactory;
     
    	public PepperoniPizza(PizzaIngredientFactory ingredientFactory) { 
    		this.ingredientFactory = ingredientFactory;
    	}
     
    	public void prepare() { 
    		System.out.println("Preparing " + name);
    		dough = ingredientFactory.createDough();
    		sauce = ingredientFactory.createSauce();
    		cheese = ingredientFactory.createCheese();
    		veggies = ingredientFactory.createVeggies();
    		pepperoni = ingredientFactory.createPepperoni();
    	}
    }
    
    public class VeggiePizza extends Pizza { 
    	PizzaIngredientFactory ingredientFactory;
     
    	public VeggiePizza(PizzaIngredientFactory ingredientFactory) { 
    		this.ingredientFactory = ingredientFactory;
    	}
     
    	public void prepare() { 
    		System.out.println("Preparing " + name);
    		dough = ingredientFactory.createDough();
    		sauce = ingredientFactory.createSauce();
    		cheese = ingredientFactory.createCheese();
    		veggies = ingredientFactory.createVeggies();
    	}
    }
    
    public class NYPizzaIngredientFactory implements PizzaIngredientFactory { 
     
    	public Dough createDough() { 
    		return new ThinCrustDough();
    	}
     
    	public Sauce createSauce() { 
    		return new MarinaraSauce();
    	}
     
    	public Cheese createCheese() { 
    		return new ReggianoCheese();
    	}
     
    	public Veggies[] createVeggies() { 
    		Veggies veggies[] = {  new Garlic(), new Onion(), new Mushroom(), new RedPepper() };
    		return veggies;
    	}
     
    	public Pepperoni createPepperoni() { 
    		return new SlicedPepperoni();
    	}
    
    	@Override
    	public Clams createClams() { 
    		return new FreshClams();
    	}
    }
    
    public abstract class PizzaStore { 
     
    	protected abstract Pizza createPizza(String item);
     
    	public Pizza orderPizza(String type) { 
    		Pizza pizza = createPizza(type);
    		System.out.println("--- Making a " + pizza.getName() + " ---");
    		pizza.prepare();
    		pizza.bake();
    		pizza.cut();
    		pizza.box();
    		return pizza;
    	}
    }
    
    public class NYPizzaStore extends PizzaStore { 
     
    	protected Pizza createPizza(String item) { 
    		Pizza pizza = null;
    		PizzaIngredientFactory ingredientFactory = 
    			new NYPizzaIngredientFactory();
     
    		if (item.equals("cheese")) { 
      
    			pizza = new CheesePizza(ingredientFactory);
    			pizza.setName("New York Style Cheese Pizza");
      
    		} else if (item.equals("veggie")) { 
     
    			pizza = new VeggiePizza(ingredientFactory);
    			pizza.setName("New York Style Veggie Pizza");
     
    		} else if (item.equals("clam")) { 
     
    			pizza = new ClamPizza(ingredientFactory);
    			pizza.setName("New York Style Clam Pizza");
     
    		} else if (item.equals("pepperoni")) { 
    
    			pizza = new PepperoniPizza(ingredientFactory);
    			pizza.setName("New York Style Pepperoni Pizza");
     
    		} 
    		return pizza;
    	}
    }
    
    public class PizzaTestDrive { 
     
    	public static void main(String[] args) { 
    		PizzaStore nyStore = new NYPizzaStore();
    
    		Pizza pizza = nyStore.orderPizza("cheese");
    		System.out.println("Ethan ordered a " + pizza + "\n");
    
    		pizza = nyStore.orderPizza("clam");
    		System.out.println("Ethan ordered a " + pizza + "\n");
    
    		pizza = nyStore.orderPizza("pepperoni");
    		System.out.println("Ethan ordered a " + pizza + "\n");
    
    		pizza = nyStore.orderPizza("veggie");
    		System.out.println("Ethan ordered a " + pizza + "\n");
    	}
    }

## 2.5 JDK ##

*  [java.lang.StringBuilder][]
 *  [java.nio.ByteBuffer][]
 *  [java.lang.StringBuffer][]
 *  [java.lang.Appendable][]
 *  [Apache Camel builders][]

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[java.util.Calendar]: http://docs.oracle.com/javase/8/docs/api/java/util/Calendar.html#getInstance--
[java.util.ResourceBundle]: http://docs.oracle.com/javase/8/docs/api/java/util/ResourceBundle.html#getBundle-java.lang.String-
[java.text.NumberFormat]: http://docs.oracle.com/javase/8/docs/api/java/text/NumberFormat.html#getInstance--
[java.nio.charset.Charset]: http://docs.oracle.com/javase/8/docs/api/java/nio/charset/Charset.html#forName-java.lang.String-
[java.net.URLStreamHandlerFactory]: http://docs.oracle.com/javase/8/docs/api/java/net/URLStreamHandlerFactory.html#createURLStreamHandler-java.lang.String-
[java.util.EnumSet]: https://docs.oracle.com/javase/8/docs/api/java/util/EnumSet.html#of-E-
[javax.xml.bind.JAXBContext]: https://docs.oracle.com/javase/8/docs/api/javax/xml/bind/JAXBContext.html#createMarshaller--
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzIxMTI1MTgz_size_16_color_FFFFFF_t_70 1]: /images/20220402/89ef749699784d61884df34f79ec690f.png
[java.lang.StringBuilder]: http://docs.oracle.com/javase/8/docs/api/java/lang/StringBuilder.html
[java.nio.ByteBuffer]: http://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html#put-byte-
[java.lang.StringBuffer]: http://docs.oracle.com/javase/8/docs/api/java/lang/StringBuffer.html#append-boolean-
[java.lang.Appendable]: http://docs.oracle.com/javase/8/docs/api/java/lang/Appendable.html
[Apache Camel builders]: https://github.com/apache/camel/tree/0e195428ee04531be27a0b659005e3aa8d159d23/camel-core/src/main/java/org/apache/camel/builder