原型模式

一、定义

复制运行时的对象，克隆出一个一模一样的对象；
hashcode和引用地址不同，只有内容相同。

UML.png

原型模式：

• 浅克隆：创建一个新对象，新对象的地址指向原来的引用
• 深克隆：重新创建一个对象，不再指向原有的对象地址

基于二进制流，比new快

二、实现

实现Cloneable接口
对象克隆：

public class PrototypeImpl implements Cloneable {

    private ArrayList list = new ArrayList();

    @Override
    public PrototypeImpl clone() {

        PrototypeImpl prototype = null;
        try {
            // 对象克隆
            prototype = (PrototypeImpl)super.clone();
            // 克隆集合
            // 数组，容器，集合，对象引用需要另行克隆
            prototype.list =  (ArrayList)this.list.clone();
        }catch (CloneNotSupportedException e){
            e.printStackTrace();
        }
        return prototype;
    }
}

public class CreatePrototype extends PrototypeImpl {
    public void show(){
        System.out.println("原型模式的实现类......");
    }
}

public class TestDemo {
    public static void main(String[] args) throws CloneNotSupportedException {
        CreatePrototype prototype = new CreatePrototype();
        // 克隆出一个新的对象
        CreatePrototype prototype1= (CreatePrototype)prototype.clone();
        prototype1.show();
    }
}

三、深度克隆

public class Person implements Cloneable{

    private String name;

    private Child child;

    public String getName() {
        return name;
    }

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

    public Child getChild() {
        return child;
    }

    public void setChild(Child child) {
        this.child = child;
    }

    @Override
    protected Person clone() {
        try {
            return (Person) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", child=" + child +
                '}';
    }

    public Person(String name) {
        this.name = name;
    }
}

public class Child implements Cloneable{

    private String name;

    public String getName() {
        return name;
    }

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

    public Child(String name) {
        this.name = name;
    }

    @Override
    protected Child clone() {
        try {
            return (Child) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    public String toString() {
        return "Child{" +
                "name='" + name + '\'' +
                '}';
    }
}

public class Test {

    public static void main(String[] args) {
        Person person = new Person("父亲");
        person.setChild(new Child("孩子"));

        //Person{name='父亲', child=Child{name='孩子'}}
        System.out.println(person);

        Person clonePerson = person.clone();

        //Person{name='父亲', child=Child{name='孩子'}}
        System.out.println(clonePerson);

        //false
        System.out.println(person==clonePerson);
    }
}

浅克隆：
存在的问题：复制的是引用地址，会导致克隆对象的修改影响了原有对象。

public class Test {

    public static void main(String[] args) {
        Person person = new Person("父亲");
        person.setChild(new Child("孩子"));

        //person:Person{name='父亲', child=Child{name='孩子'}}
        System.out.println("person:"+person);

        Person clonePerson = person.clone();
        clonePerson.getChild().setName("孩子2");

        //clonePerson:Person{name='父亲', child=Child{name='孩子2'}}
        System.out.println("clonePerson:"+clonePerson);
        
        //person:Person{name='父亲', child=Child{name='孩子2'}}
        System.out.println("person:"+person);
        
    }
}

1.重写clone方法，依次调用成员变量的clone方法

    @Override
    protected Person clone() {
        try {
            Person person = (Person) super.clone();
            Child child = person.getChild().clone();
            person.setChild(child);
            return person;
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return null;
    }

public class Test {

    public static void main(String[] args) {
        Person person = new Person("父亲");
        person.setChild(new Child("孩子"));

        //person:Person{name='父亲', child=Child{name='孩子'}}
        System.out.println("person:"+person);

        Person clonePerson = person.clone();
        clonePerson.getChild().setName("孩子2");

        //clonePerson:Person{name='父亲', child=Child{name='孩子2'}}
        System.out.println("clonePerson:"+clonePerson);

        //person:Person{name='父亲', child=Child{name='孩子'}}
        System.out.println("person:"+person);

    }
}

2.通过序列化和反序列化实现

类实现序列化

public class Person implements Cloneable,Serializable
public class Child implements Cloneable, Serializable

    @Override
    protected Person clone() {
        ByteArrayOutputStream byteArrayOutputStream =null;
        ObjectOutputStream objectOutputStream =null;
        ByteArrayInputStream byteArrayInputStream =null;
        ObjectInputStream objectInputStream =null;
        try {
            byteArrayOutputStream = new ByteArrayOutputStream();
            objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);
            objectOutputStream.writeObject(this);

            byteArrayInputStream = new ByteArrayInputStream(byteArrayOutputStream.toByteArray());
            objectInputStream = new ObjectInputStream(byteArrayInputStream);
            Person person = (Person)objectInputStream.readObject();
            return person;
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            try {
                byteArrayOutputStream.close();
                byteArrayInputStream.close();
                objectOutputStream.close();
                objectInputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

3.使用工具类来实现序列化和反序列化

• BeanUtils
• MapStruct