一文带你了解Java设计模式之原型模式

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2023-02-03
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标签   Java设计模式
目录
  • 定义
  • 解决的问题
  • 核心要点
  • 类图
  • 浅复制与深复制的区别
  • 代码实现
  • 未使用设计模式
  • 实现Cloneable接口
  • 深复制-重写clone
  • 深复制-通过对象序列化实现（推荐）
  • 拓展

定义

用原型实例指定创建对象的种类，并且通过拷贝这些原型创建新的对象。

原型模式其实就是从一个对象在创建另外一个可定制的对象，不需要知道任何创建的细节

解决的问题

在运行期建立和删除原型。

经常用于：

类初始化消耗资源较多

构造函数比较复杂

核心要点

1.实现cloneable 接口，重写Object的clone方法

2.利用已有的一个原型对象，快速地生成和原型对象一样的实例。

类图

浅复制与深复制的区别

浅复制：基本数据类型进行值传递、引用数据类型的指针仍是指向原来的对象（成员变量）。

深复制：基本数据类型进行值传递、引用数据类型开辟新的内存空间。

代码实现

需求：实现克隆羊

有一头羊，需要经过赋值再克隆出两头。

未使用设计模式

/**
 * 克隆羊类
 *
 * @author Promsing(张有博)
 * @version 1.0.0
 * @since 2022/9/3 - 14:51
 */
public class Sheep {
 
    private String name;
 
    private Integer age;
 
    private String color;
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }
 
    public String getColor() {
        return color;
    }
 
    public void setColor(String color) {
        this.color = color;
    }
 
    public Sheep() {
    }
 
    public Sheep(String name, Integer age, String color) {
        this.name = name;
        this.age = age;
        this.color = color;
    }
}

Main方法

/**
 * 
 * 传统模式
 * @author Promsing(张有博)
 * @version 1.0.0
 * @since 2022/9/3 - 14:47
 */
public class Client {
 
    public static void main(String[] args) {
        //小羊
        Sheep sheep=new Sheep("小红",8,"红色");
        //克隆羊
        Sheep sheep2=sheep;
        Sheep sheep3=sheep;
 
        System.out.println("通过赋值，指针还是指向sheep");
        System.out.println(sheep);
        System.out.println(sheep2);
        System.out.println(sheep3);
        
    }
 
}
 
//通过赋值，指针还是指向sheep
//com.promsing.creational.prototype.type1.Sheep@1b6d3586
//com.promsing.creational.prototype.type1.Sheep@1b6d3586
//com.promsing.creational.prototype.type1.Sheep@1b6d3586

实现Cloneable接口

Cloneable是标记型的接口，它们内部都没有方法和属性，实现 Cloneable来表示该对象能被克隆，能使用Object.clone()方法。

如果没有实现 Cloneable的类对象调用clone()就会抛出CloneNotSupportedException。

实现Cloneable默认是浅复制

/**
 * 克隆羊
 *
 * @author Promsing(张有博)
 * @version 1.0.0
 * @since 2022/9/3 - 14:53
 */
public class Sheep implements Cloneable {
 
    private String name;
 
    private Integer age;
 
    private String color;
 
    /**
     * 羊的朋友
     */
    private Sheep friend;
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }
 
    public String getColor() {
        return color;
    }
 
    public void setColor(String color) {
        this.color = color;
    }
 
    public Sheep() {
    }
 
    public Sheep getFriend() {
        return friend;
    }
 
    public void setFriend(Sheep friend) {
        this.friend = friend;
    }
 
    public Sheep(String name, Integer age, String color) {
        this.name = name;
        this.age = age;
        this.color = color;
    }
 
 
    /**
     * 克隆该实例，调用object.clone的方法
     * @return
     */
    @Override
    protected Sheep clone() {
 
        Sheep sheep = null;
        try {
            sheep = (Sheep) super.clone();
 
        } catch (CloneNotSupportedException e) {
            System.out.println(e.getMessage());
            e.printStackTrace();
        }
        return sheep;
    }
}

Main方法

/**
 * 浅复制：浅复制：基本数据类型进行值传递、引用数据类型的指针仍是指向原来的对象（成员变量）。
 */
public class ShallowClient {
 
    public static void main(String[] args) {
 
        Sheep sheep=new Sheep("小红",9,"红色");
        sheep.setFriend(new Sheep("小黑",10,"黑色"));
        Sheep sheep1 = sheep.clone();//开辟了新的空间
        Sheep sheep2 = sheep.clone();
 
        //浅复制
        System.out.println("原型羊"+sheep);
        System.out.println("克隆羊"+sheep1+"-朋友羊-"+sheep1.getFriend());
        System.out.println("克隆羊"+sheep2+"-朋友羊-"+sheep2.getFriend());
        
//原型羊com.promsing.creational.prototype.type3.Sheep@1b6d3586
//克隆羊com.promsing.creational.prototype.type3.Sheep@4554617c-朋友羊-com.promsing.creational.prototype.type3.Sheep@74a14482
//克隆羊com.promsing.creational.prototype.type3.Sheep@1540e19d-朋友羊-com.promsing.creational.prototype.type3.Sheep@74a14482
 
 
    }
 
}

一定要实现接口cloneable 否则报错：

Exception in thread "main" java.lang.CloneNotSupportedException: com.promsing.creational.prototype.type4.Sheep
   at java.lang.Object.clone(Native Method)
   at com.promsing.creational.prototype.type4.Sheep.clone(Sheep.java:76)
   at com.promsing.creational.prototype.type4.DeepClient.main(DeepClient.java:14)

深复制-重写clone

羊类、房子类都需要实现Cloneable接口

房子类

/**
 * 房子类
 *
 * @author Promsing(张有博)
 * @version 1.0.0
 * @since 2022/9/3 - 15:27
 */
public class House implements Cloneable {
 
    //地址
    private String address;
 
    //尺寸
    private Integer size;
 
    public String getAddress() {
        return address;
    }
 
    public void setAddress(String address) {
        this.address = address;
    }
 
    public Integer getSize() {
        return size;
    }
 
    public void setSize(Integer size) {
        this.size = size;
    }
 
 
    /**
     * 克隆的方法
     * @return
     * @throws CloneNotSupportedException
     */
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

羊类

/**
 * 克隆羊-深拷贝
 *
 * @author Promsing(张有博)
 * @version 1.0.0
 * @since 2022/9/3 - 15:26
 */
public class Sheep implements  Cloneable {
 
    private String name;
 
    private Integer age;
 
    private String color;
 
    /**
     * 羊的房子:引用类型
     */
    private House house;
 
    public House getHouse() {
        return house;
    }
 
    public void setHouse(House house) {
        this.house = house;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }
 
    public String getColor() {
        return color;
    }
 
    public void setColor(String color) {
        this.color = color;
    }
 
    public Sheep() {
    }
 
 
    public Sheep(String name, Integer age, String color) {
        this.name = name;
        this.age = age;
        this.color = color;
    }
 
    /**
     * 克隆该实例，调用object，clone的方法
     *
     * @return
     * @throws CloneNotSupportedException
     */
    @Override
    protected Object clone() throws CloneNotSupportedException {
 
        //对基本数据类型进行处理
        Sheep deep = null;
        deep = (Sheep) super.clone();
 
        //对引用类型进行处理
        //进行再次克隆
        House clone = (House) deep.getHouse().clone();
        deep.setHouse(clone);
 
        return deep;
    }
 
   
}

Main

/**
 * 深复制:羊类、房子类都需要重写clone的接口，比较麻烦。不符合开闭
 *
 * @author Promsing(张有博)
 * @version 1.0.0
 * @since 2022/9/3 - 15:38
 */
public class DeepClient {
 
    public static void main(String[] args) throws CloneNotSupportedException {
        Sheep sheep=new Sheep("黑",90,"heisee");
        sheep.setHouse(new House());
        Sheep clone = (Sheep)sheep.clone();
        System.out.println("原本的对象");
        System.out.println(sheep);
        System.out.println(sheep.getHouse());
        System.out.println("克隆的对象");
        System.out.println(clone);
        System.out.println(clone.getHouse());
        
        
        //开辟了新的内存空间
        //原本的对象
        //com.promsing.creational.prototype.type4.Sheep@1b6d3586
        //com.promsing.creational.prototype.type4.House@4554617c
        //克隆的对象
        //com.promsing.creational.prototype.type4.Sheep@74a14482
        //com.promsing.creational.prototype.type4.House@1540e19d
    }
 
}

深复制-通过对象序列化实现（推荐）

羊类、房子类都需要实现Serializable接口。注意这里可以不实现Cloneable了。

房子类

/**
 * 房子类
 *
 * @author Promsing(张有博)
 * @version 1.0.0
 * @since 2022/9/3 - 15:27
 */
public class House implements Serializable{
 
    //地址
    private String address;
 
    //尺寸
    private Integer size;
 
    public String getAddress() {
        return address;
    }
 
    public void setAddress(String address) {
        this.address = address;
    }
 
    public Integer getSize() {
        return size;
    }
 
    public void setSize(Integer size) {
        this.size = size;
    }
 
}

羊类

/**
 * 克隆羊-深拷贝
 *
 * @author Promsing(张有博)
 * @version 1.0.0
 * @since 2022/9/3 - 15:26
 */
public class Sheep implements Serializable {
 
    private String name;
 
    private Integer age;
 
    private String color;
 
    /**
     * 羊的房子:引用类型
     */
    private House house;
 
    public House getHouse() {
        return house;
    }
 
    public void setHouse(House house) {
        this.house = house;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }
 
    public String getColor() {
        return color;
    }
 
    public void setColor(String color) {
        this.color = color;
    }
 
    public Sheep() {
    }
 
 
    public Sheep(String name, Integer age, String color) {
        this.name = name;
        this.age = age;
        this.color = color;
    }
 
 
    /**
     * 序列化的方式：进行深复制
     * 写着麻烦：用着简单。支持开闭原则
     * @return
     */
    public Object deepClone() {
 
        //创建流对象
        ByteArrayOutputStream bos = null;
        ObjectOutputStream oos = null;
        ByteArrayInputStream bis = null;
        ObjectInputStream ois = null;
 
        try {
 
            //序列化
            bos = new ByteArrayOutputStream();
            oos = new ObjectOutputStream(bos);
            oos.writeObject(this); //当前这个对象以对象流的方式输出
 
            //反序列化
            bis = new ByteArrayInputStream(bos.toByteArray());
            ois = new ObjectInputStream(bis);
            Sheep copyObj = (Sheep) ois.readObject();
 
            return copyObj;
 
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
            return null;
        } finally {
            //关闭流
            try {
                bos.close();
                oos.close();
                bis.close();
                ois.close();
            } catch (Exception e2) {
                // TODO: handle exception
                System.out.println(e2.getMessage());
            }
        }
 
    }
}

Main

/**
 * 深复制
 *
 * @author Promsing(张有博)
 * @version 1.0.0
 * @since 2022/9/3 - 15:38
 */
public class DeepClient {
 
    public static void main(String[] args) throws CloneNotSupportedException {
        Sheep sheep=new Sheep("黑",90,"heisee");
        sheep.setHouse(new House());
        Sheep clone = (Sheep)sheep.deepClone();
        System.out.println("原本的对象");
        System.out.println(sheep);
        System.out.println(sheep.getHouse());
        System.out.println("克隆的对象");
        System.out.println(clone);
        System.out.println(clone.getHouse());
    }
 
}

拓展

Spring使用原型模式：@scope(“prototype”)

public static void main(String[] args) throws IOException {
      //new一个容器
    AnnotationConfigWebApplicationContext context =
        new AnnotationConfigWebApplicationContext();
    System.out.println("run success");
 
    OrderService bean = context.getBean(OrderService.class);
}
 
//根据getBean点进去
public <T> T getBean(Class<T> requiredType) throws BeansException {
		assertBeanFactoryActive();
		return getBeanFactory().getBean(requiredType);
}
 
public Object getBean(String name) throws BeansException {
		return doGetBean(name, null, null, false);
}

后续走到了。AbstractBeanFactory类中的doGetBean方法中里边代码做判断mbd.isPrototype()

protected <T> T doGetBean(
			String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
			throws BeansException {
 
		String beanName = transformedBeanName(name);
		Object bean;
 
		// Eagerly check singleton cache for manually registered singletons.
		Object sharedInstance = getSingleton(beanName);
		if (sharedInstance != null && args == null) {
			//代码省略~~~~
		}
 
		else {
			//代码省略~~~~
 
			
			try {
				//代码省略~~~~
        
				// Create bean instance.
        //判断是否是单例
				if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, () -> {
						try {
							return createBean(beanName, mbd, args);
						}
						catch (BeansException ex) {
							
							destroySingleton(beanName);
							throw ex;
						}
					});
					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}
        //判断是否是多例（原型）
        //这里会创建一个新的对象
				else if (mbd.isPrototype()) {
					// It's a prototype -> create a new instance.
					Object prototypeInstance = null;
					try {
						beforePrototypeCreation(beanName);
						prototypeInstance = createBean(beanName, mbd, args);
					}
					finally {
						afterPrototypeCreation(beanName);
					}
					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
				}
 
				else {
					//代码省略~~~~
				}
			}
			catch (BeansException ex) {
				cleanupAfterBeanCreationFailure(beanName);
				throw ex;
			}
		}
 
		//代码省略~~~~
		}
		return (T) bean;
	}

ArrayList实现了Cloneable接口

public Object clone() {
    try {
        ArrayList<?> v = (ArrayList<?>) super.clone();
        v.elementData = Arrays.copyOf(elementData, size);
        v.modCount = 0;
        return v;
    } catch (CloneNotSupportedException e) {
        // this shouldn't happen, since we are Cloneable
        throw new InternalError(e);
    }
}
Spring Boot自定义 Starter并推送到远端公服的详细代码
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