Prototype模式

简介

用于创建重复的对象，同时又能保证性能。这种类型的设计模式属于创建型模式，它提供了一种创建对象的最佳方式。这种模式是实现了一个原型接口，该接口用于创建当前对象的克隆。当直接创建对象的代价比较大时，则采用这种模式。

什么情况下使用原型设计模式呢？

一个对象需要在一个高代价的数据库操作之后被创建。我们可以缓存该对象，在下一个请求时返回它的克隆，在需要的时候更新数据库，以此来减少数据库调用。

实现方式

• c++
  c++中可以通过实现拷贝构造函数的方法实现，要注意深拷贝和浅拷贝的问题。
• java
  • 实现Cloneable接口，并覆写clone方法;
  • 使用对象流。使用对象流，所有的自定义类型需要实现Serializable接口。

prototype.png

抽象原型

class Prototype {
public:
    virtual Prototype * clone() = 0;
};

具体原型

class ContretePrototype :public Prototype {
private:
    char *name;
    int id;
public:
    ContretePrototype(const char *name, int id) {
        this->name = NULL;
        if (name != NULL) {
            //this->name = (char *)malloc(sizeof(char)*(strlen(name) + 1));
            this->name = new char[sizeof(char)*(strlen(name) + 1)];
            strcpy(this->name, name);
        }
        this->id = id;
    }
    ContretePrototype(const ContretePrototype& prototype) {
        this->name = NULL;
        if (prototype.getName() != NULL) {
            this->name = (char *)malloc(sizeof(char)*(strlen(prototype.getName()) + 1));
            strcpy(this->name, prototype.getName());
        }
        this->id = prototype.getId();
    }

    Prototype * clone() {
        ContretePrototype *prototype = new ContretePrototype(*this);
        return prototype;
    }
    ~ContretePrototype() {
        if (this->name != NULL) {
            //free (this->name);
            delete[]this->name;
        }
    }

    int getId()const {
        return this->id;
    }

    char * getName()const {
        return this->name;
    }
};

测试

int main()
{
    ContretePrototype p("abc", 1);
    cout << p.getName() << "  " << p.getId() << endl;
    ContretePrototype *p1 =dynamic_cast( p.clone());
    cout << p1->getName() << "  " << p1->getId() << endl;
    delete p1;
    return 0;
}

prototype_res.png

Java版

public class A  implements Cloneable,Serializable {
    private int x;
    private int y;

    public A(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    protected Object clone()   {
        Object o=null;
        try {
            o=(A)super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return o;
    }

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getY() {
        return y;
    }

    public void setY(int y) {
        this.y = y;
    }

    @Override
    public String toString() {
        return "A{" +
                "x=" + x +
                ", y=" + y +
                '}';
    }
}

public class Prototype implements Cloneable, Serializable {
    private List list;
    private A a;
    private int id;
    private String name;

    @Override
    protected Object clone() {
        Prototype o = null;
        try {
            o = (Prototype) super.clone();
            o.setA((A) o.getA().clone());
            List temp = new ArrayList(o.getList().size());
            for (A a : o.getList()) {
                temp.add((A) a.clone());
            }
            o.setList(temp);
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return o;
    }

    public Object deepClone() throws IOException, ClassNotFoundException {
        //将对象写到流里
        ByteArrayOutputStream bo = new ByteArrayOutputStream();
        ObjectOutputStream oo = new ObjectOutputStream(bo);
        oo.writeObject(this);
        //从流里读出来
        ByteArrayInputStream bi = new ByteArrayInputStream(bo.toByteArray());
        ObjectInputStream oi = new ObjectInputStream(bi);
        return (oi.readObject());
    }

    public List getList() {
        return list;
    }

    public void setList(List list) {
        this.list = list;
    }

    public A getA() {
        return a;
    }

    public void setA(A a) {
        this.a = a;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "Prototype{" +
                "list=" + list +
                ", a=" + a +
                ", id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

public class Test {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        //构造对象
        Prototype prototype = new Prototype();
        List list = new ArrayList();
        A a1 = new A(1, 2);
        A a2 = new A(10, 20);
        list.add(a1);
        list.add(a2);
        prototype.setList(list);
        A a3 = new A(100, 200);
        prototype.setA(a3);
        prototype.setId(1000);
        prototype.setName("prototype name");
        //打印对象内容
        log(prototype.toString());
        //使用clone克隆
        Prototype p1 = (Prototype) prototype.clone();
        //查看克隆后的结果
        log(p1.toString());
        //使用对象流序列化
        Prototype p2 = (Prototype) p1.deepClone();
        p1.getA().setX(300);
        p1.getList().get(0).setX(3000);
        log(prototype.toString());
        log(p2.toString());
    }


    public static void log(String content) {
        System.out.println(content);
    }
}

结果

Prototype{list=[A{x=1, y=2}, A{x=10, y=20}], a=A{x=100, y=200}, id=1000, name='prototype name'}
Prototype{list=[A{x=1, y=2}, A{x=10, y=20}], a=A{x=100, y=200}, id=1000, name='prototype name'}
Prototype{list=[A{x=1, y=2}, A{x=10, y=20}], a=A{x=100, y=200}, id=1000, name='prototype name'}
Prototype{list=[A{x=1, y=2}, A{x=10, y=20}], a=A{x=100, y=200}, id=1000, name='prototype name'}

Process finished with exit code 0