Spring设计模式——原型模式

原型模式

原型模式(Prototype Pattern)，是指原型实例指定创建对象的种类，并且通过复制这些原型创建新的对象。

原型模式主要适用于以下场景：

1. 类初始化消耗资源较多
2. 使用new生成一个对象需要非常繁琐的过程（数据准备、访问权限等）
3. 构造函数比较复杂
4. 在循环中产生大量对象

浅拷贝

先创建原型Prototype接口：

/**
 * @author ss_419
 */
public interface Prototype {
    Prototype clone();
}

创建具体需要克隆的类ConcretePrototypeA：

package org.example.spring.designpattern.prototype.shallow;

import java.util.List;

/**
 * TODO
 *
 * @author ss_419
 * @version 1.0
 * @date 2023/3/9 09:15
 */
public class ConcretePrototypeA implements Prototype {
    private int age;
    private String name;
    private List hobbies;

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List getHobbies() {
        return hobbies;
    }

    public void setHobbies(List hobbies) {
        this.hobbies = hobbies;
    }

    @Override
    public Prototype clone() {
        ConcretePrototypeA concretePrototypeA = new ConcretePrototypeA();
        concretePrototypeA.setAge(this.getAge());
        concretePrototypeA.setName(this.getName());
        concretePrototypeA.setHobbies(this.getHobbies());
        return concretePrototypeA;
    }

    @Override
    public String toString() {
        return "ConcretePrototypeA{" +
                "age=" + age +
                ", name='" + name + '\'' +
                ", hobbies=" + hobbies +
                '}';
    }
}

创建Client类：

package org.example.spring.designpattern.prototype.shallow;

/**
 * TODO
 *
 * @author ss_419
 * @version 1.0
 * @date 2023/3/9 09:17
 */
public class Client {
    private Prototype prototype;

    public Client(Prototype prototype) {
        this.prototype = prototype;
    }
    public Prototype startClone(Prototype concretePrototype){
        return (Prototype) concretePrototype.clone();
    }
}

测试代码如下：

package org.example.spring.designpattern.prototype.shallow;

import java.util.ArrayList;
import java.util.List;

/**
 * TODO
 *
 * @author ss_419
 * @version 1.0
 * @date 2023/3/9 09:20
 */
public class PrototypeTest {
    public static void main(String[] args) {
        ConcretePrototypeA concretePrototypeA = new ConcretePrototypeA();
        concretePrototypeA.setAge(18);
        concretePrototypeA.setName("ss");
        List hobbies = new ArrayList<String>();
        hobbies.add("唱");
        hobbies.add("跳");
        hobbies.add("Rap");
        concretePrototypeA.setHobbies(hobbies);
        System.out.println(concretePrototypeA);

        // 创建client对象，准备开始克隆
        Client client = new Client(concretePrototypeA);
        ConcretePrototypeA concretePrototypeClone = (ConcretePrototypeA) client.startClone(concretePrototypeA);
        System.out.println(concretePrototypeClone);

        System.out.println("concretePrototypeA.getHobbies() = " + concretePrototypeA.getHobbies());
        System.out.println("concretePrototypeClone.getHobbies() = " + concretePrototypeClone.getHobbies());
        System.out.println("对象地址比较：" +(concretePrototypeClone.getHobbies() == concretePrototypeA.getHobbies()));
    }
}

浅拷贝只是完整复制了值类型数据，没有赋值引用对象，换言之，所有的引用对象仍然指向原来的对象，显然这不是我们想要的结果。

深拷贝

创建原型猴子类Monkey：

package org.example.spring.designpattern.prototype.deep;

import java.util.Date;

/**
 * TODO 深拷贝对象——猴子
 *
 * @author ss_419
 * @version 1.0
 * @date 2023/3/9 09:41
 */
public class Monkey {
    public int height;
    public int weight;
    public Date birthDate;
}

创建引用对象JinGuBang：

package org.example.spring.designpattern.prototype.deep;

import java.io.Serializable;

/**
 * TODO 引用对象JinGuBang
 *
 * @author ss_419
 * @version 1.0
 * @date 2023/3/9 09:43
 */
public class JinGuBang implements Serializable {
    public float h = 100;
    public float d = 10;

    public void big(){
        this.d *= 2;
        this.h *= 2;
    }
    public void small(){
        this.d /= 2;
        this.h /= 2;
    }
}

创建具体的对象齐天大圣类QiTianDaSheng：

package org.example.spring.designpattern.prototype.deep;

import java.io.*;
import java.util.Date;

/**
 * TODO 具体对象齐天大圣，归根结底还是个猴儿～
 *
 * @author ss_419
 * @version 1.0
 * @date 2023/3/9 09:45
 */
public class QiTianDaSheng extends Monkey implements Cloneable, Serializable {
    public JinGuBang jinGubang;

    public QiTianDaSheng() {
        // 只是初始化
        this.birthDate = new Date();
        this.jinGubang = new JinGuBang();
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        // 调用指定的拷贝方法(深deep、浅shallow)
        return this.deepClone();
    }

    // 深拷贝
    public Object deepClone() {
        try{
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            ObjectOutputStream oos = new ObjectOutputStream(bos);
            // 写入当前对象
            oos.writeObject(this);

            ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
            ObjectInputStream ois = new ObjectInputStream(bis);

            QiTianDaSheng copy = (QiTianDaSheng)ois.readObject();
            copy.birthDate = new Date();
            return copy;
        }catch (Exception e){
            e.printStackTrace();
            return null;
        }
    }

    public QiTianDaSheng shallowClone(QiTianDaSheng target){
        QiTianDaSheng qiTianDaSheng = new QiTianDaSheng();
        qiTianDaSheng.height = target.height;
        qiTianDaSheng.weight = target.weight;

        qiTianDaSheng.jinGubang = target.jinGubang;
        qiTianDaSheng.birthDate = new Date();

        return qiTianDaSheng;
    }
}

测试代码如下：

package org.example.spring.designpattern.prototype.deep;

/**
 * TODO 深拷贝测试代码
 *
 * @author ss_419
 * @version 1.0
 * @date 2023/3/9 09:53
 */
public class DeepCloneTest {
    public static void main(String[] args) {
        QiTianDaSheng qiTianDaSheng = new QiTianDaSheng();
        try {
            QiTianDaSheng clone
                    = (QiTianDaSheng) qiTianDaSheng.clone();
            System.out.println("深拷贝：" + (qiTianDaSheng.jinGubang == clone.jinGubang));
        }catch (Exception e){
            e.printStackTrace();
        }
        QiTianDaSheng q = new QiTianDaSheng();
        QiTianDaSheng n = q.shallowClone(q);
        System.out.println("浅拷贝：" + (q.jinGubang == n.jinGubang));

    }
}

运行结果如下：



我们可以发现，深拷贝的引用类对象是不同的指向，而浅拷贝的引用地址是相同的，这意味着深拷贝复制的是值，而不是引用地址了。