23种设计模式(三)原型模式

矫情吗；* 2022-12-29 14:03 117阅读 0赞

### 原型模式 ###

**原型模式的适用场景：**

> 1.类初始化消耗资源较多  
> 2.new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.循环产生大量对象时

**优点：**

> 1.原型模式比new一个对象性能要高  
> 2.简化创建过程

**缺点：**

> 1.必须配备克隆方法（必须重写object的克隆方法）  
> 2.对克隆对象，进行复杂改造的时候，容易引入风险

**重要的是克隆**  
常用的场景：积分抽奖，邮箱，短信  
**浅克隆：**

> Cloneable接口 重写clone方法

public class Email implements Cloneable{ 
        private String name;
        private String address;
        private String content;
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public String getAddress() { 
            return address;
        }
    
        public void setAddress(String address) { 
            this.address = address;
        }
    
        public String getContent() { 
            return content;
        }
    
        public void setContent(String content) { 
            this.content = content;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException { 
            return super.clone();
        }
    
        @Override
        public String toString() { 
            return "Email{" +
                    "name='" + name + '\'' +
                    ", address='" + address + '\'' +
                    ", content='" + content + '\'' +
                    '}'+super.toString();
        }
    }

发送邮件，保存邮件内容

public class EmailUtils { 
        public static void sendEmail(Email email){ 
            String sendfriend="向{0}发送,邮件地址:{1},邮件内容:{2}";
            System.out.println(MessageFormat.format(sendfriend, email.getName(),email.getAddress(),email.getContent()));
        }
        public static void saveOriginMailRecord(Email email){ 
            System.out.println("存储原始email:"+email.getContent());
        }
    }

Email clone=(Email)email.clone(); 克隆

public class Test { 
        public static void main(String[] args) throws CloneNotSupportedException { 
            Email email=new Email();
            email.setContent("测试模板");
            System.out.println(email);
            for (int i = 0; i < 10; i++) { 
                Email clone=(Email)email.clone();
                clone.setName("姓名"+i);
                clone.setAddress("qq号"+i+"@qq.com");
                clone.setContent("恭喜您中奖qq币");
                EmailUtils.sendEmail(clone);
                System.out.println("CLONE"+clone);
            }
            EmailUtils.saveOriginMailRecord(email);
        }
    }

输出结果

Email{ name='null', address='null', content='测试模板'}com.qjc.pattern.creational.prototype.Email@4554617c
    向姓名0发送,邮件地址:qq号0@qq.com,邮件内容:恭喜您中奖qq币
    CLONEEmail{ name='姓名0', address='qq号0@qq.com', content='恭喜您中奖qq币'}com.qjc.pattern.creational.prototype.Email@74a14482
    向姓名1发送,邮件地址:qq号1@qq.com,邮件内容:恭喜您中奖qq币
    CLONEEmail{ name='姓名1', address='qq号1@qq.com', content='恭喜您中奖qq币'}com.qjc.pattern.creational.prototype.Email@1540e19d
    向姓名2发送,邮件地址:qq号2@qq.com,邮件内容:恭喜您中奖qq币
    CLONEEmail{ name='姓名2', address='qq号2@qq.com', content='恭喜您中奖qq币'}com.qjc.pattern.creational.prototype.Email@677327b6
    向姓名3发送,邮件地址:qq号3@qq.com,邮件内容:恭喜您中奖qq币
    CLONEEmail{ name='姓名3', address='qq号3@qq.com', content='恭喜您中奖qq币'}com.qjc.pattern.creational.prototype.Email@14ae5a5
    向姓名4发送,邮件地址:qq号4@qq.com,邮件内容:恭喜您中奖qq币
    CLONEEmail{ name='姓名4', address='qq号4@qq.com', content='恭喜您中奖qq币'}com.qjc.pattern.creational.prototype.Email@7f31245a
    向姓名5发送,邮件地址:qq号5@qq.com,邮件内容:恭喜您中奖qq币
    CLONEEmail{ name='姓名5', address='qq号5@qq.com', content='恭喜您中奖qq币'}com.qjc.pattern.creational.prototype.Email@6d6f6e28
    向姓名6发送,邮件地址:qq号6@qq.com,邮件内容:恭喜您中奖qq币
    CLONEEmail{ name='姓名6', address='qq号6@qq.com', content='恭喜您中奖qq币'}com.qjc.pattern.creational.prototype.Email@135fbaa4
    向姓名7发送,邮件地址:qq号7@qq.com,邮件内容:恭喜您中奖qq币
    CLONEEmail{ name='姓名7', address='qq号7@qq.com', content='恭喜您中奖qq币'}com.qjc.pattern.creational.prototype.Email@45ee12a7
    向姓名8发送,邮件地址:qq号8@qq.com,邮件内容:恭喜您中奖qq币
    CLONEEmail{ name='姓名8', address='qq号8@qq.com', content='恭喜您中奖qq币'}com.qjc.pattern.creational.prototype.Email@330bedb4
    向姓名9发送,邮件地址:qq号9@qq.com,邮件内容:恭喜您中奖qq币
    CLONEEmail{ name='姓名9', address='qq号9@qq.com', content='恭喜您中奖qq币'}com.qjc.pattern.creational.prototype.Email@2503dbd3
    存储原始email:测试模板

由此看出new对象一次，然后使用clone方法频繁复制对象

**深克隆：**  
深克隆，就是对象里面包含了一个date对象如果在引用时

public class Pig  implements Cloneable{ 
        private String name;
        private Date birthday;
    
        public Pig(String name, Date birthday) { 
            this.name = name;
            this.birthday = birthday;
        }
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public Date getBirthday() { 
            return birthday;
        }
    
        public void setBirthday(Date birthday) { 
            this.birthday = birthday;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException { 
            //深克隆 很容易引起bug
            return super.clone();
        }
    
        @Override
        public String toString() { 
            return "Pig{" +
                    "name='" + name + '\'' +
                    ", birthday=" + birthday +
                    '}'+super.toString();
        }
    }

//深克隆 浅克隆
            Date date=new Date(0L);
            Pig pig=new Pig("佩奇",date);
            Pig pig1= (Pig) pig.clone();
            System.out.println(pig);//date 引用的同一个对象
            System.out.println(pig1);//date
           
            pig.getBirthday().setTime(8888888888L);
            //相同对象
            System.out.println(pig);
            System.out.println(pig1);

输出结果：

Pig{ name='佩奇', birthday=Thu Jan 01 08:00:00 CST 1970}com.qjc.pattern.creational.prototype.clone.Pig@14ae5a5
    Pig{ name='佩奇', birthday=Thu Jan 01 08:00:00 CST 1970}com.qjc.pattern.creational.prototype.clone.Pig@7f31245a
    Pig{ name='佩奇', birthday=Tue Apr 14 05:08:08 CST 1970}com.qjc.pattern.creational.prototype.clone.Pig@14ae5a5
    Pig{ name='佩奇', birthday=Tue Apr 14 05:08:08 CST 1970}com.qjc.pattern.creational.prototype.clone.Pig@7f31245a

由此看出如果我修改了date，导致克隆对象也会被修改，这就是深克隆的问题  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyNzMxMzU4_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyNzMxMzU4_size_16_color_FFFFFF_t_70 1]  
如何解决此问题，重写clone方法

@Override
        protected Object clone() throws CloneNotSupportedException { 
            Pig pig=(Pig)super.clone();
            pig.birthday= (Date) pig.birthday.clone();
            return pig;
        }

Pig{ name='佩奇', birthday=Thu Jan 01 08:00:00 CST 1970}com.qjc.pattern.creational.prototype.clone.Pig@14ae5a5
    Pig{ name='佩奇', birthday=Thu Jan 01 08:00:00 CST 1970}com.qjc.pattern.creational.prototype.clone.Pig@7f31245a
    Pig{ name='佩奇', birthday=Tue Apr 14 05:08:08 CST 1970}com.qjc.pattern.creational.prototype.clone.Pig@14ae5a5
    Pig{ name='佩奇', birthday=Thu Jan 01 08:00:00 CST 1970}com.qjc.pattern.creational.prototype.clone.Pig@7f31245a

这样的话date对象就不存在深克隆这个问题了  
jdk中有：  
HashMap，ArrayList 等实现了Cloneable接口有兴趣的参考一下

克隆破坏单例模式：懒汉式 这样的话就会出现两个对象

HungrySingleton hungrySingleton = HungrySingleton.getInstance();
            Method method = hungrySingleton.getClass().getDeclaredMethod("clone");
            method.setAccessible(true);
            HungrySingleton cloneHungrySingleton = (HungrySingleton) method.invoke(hungrySingleton);
            System.out.println(hungrySingleton);
            System.out.println(cloneHungrySingleton);

如何防止这种方式，不实现Cloneable接口，或者让Cloneable,调用另一个方法getInstatance，即可解决

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyNzMxMzU4_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20201223120813356.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyNzMxMzU4,size_16,color_FFFFFF,t_70