关于java:我所知道设计模式之原型模式

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前言需要

接下里介绍的是 Java 的设计模式之一：原型模式

当初有一只羊 tom

姓名为: tom, 年龄为：1，色彩为：红色

请编写程序创立和 tom 羊 属性完全相同的 10 只羊

请问你会怎么制作呢？

一、什么是原型模式

原型模式 (Prototype 模式) 是指：用原型实例指定创建对象的品种，并且通过拷贝这些原型，创立新的对象

原型模式是一种创立型设计模式，容许一个对象再创立另外一个可定制的对象，无需晓得如何创立的细节

工作原理是:通过将一个原型对象传给那个要动员创立的对象，这个要动员创立的对象通过申请原型对象拷贝它们本人来施行创立，即对象.clone()

形象的了解：齐天大圣孙悟空插入猴毛，变出其它孙大圣

原理结构图阐明
Prototype : 原型类，申明一个克隆本人的接口
ConcretePrototype: 具体的原型类, 实现一个克隆本人的操作
Client: 让一个原型对象克隆本人，从而创立一个新的对象(属性一样）

二、通过示例阐明状况

咱们依照传统形式解决之前提出的克隆羊问题

class Sheep{
 
    public String name;
 
    public int age;
 
    public String color;
 
    public Sheep(String name, int age, String color) {
        this.name = name;
        this.age = age;
        this.color = color;
    }
 
    public String   getName() {return name;}
 
    public void setName(String name) {this.name = name;}
 
    public int getAge() {return age;}
 
    public void setAge(int age) {this.age = age;}
 
    public String getColor() {return color;}
 
    public void setColor(String color) {this.color = color;}
}

咱们生成一只羊，而后依据这只羊的属性创立十只羊

public static void main(String[] args) {
        // 传统的办法
        Sheep sheep = new Sheep("tom", 1, "红色");
        Sheep sheep2 = new Sheep(sheep.getName(), sheep.getAge(), sheep.getColor());
        Sheep sheep3 = new Sheep(sheep.getName(), sheep.getAge(), sheep.getColor());
        Sheep sheep4 = new Sheep(sheep.getName(), sheep.getAge(), sheep.getColor());
        
        //.........
    }

传统的形式的优缺点

  • 长处是 比拟好了解，简略易操作。
  • 在 创立新的对象时，总是须要从新获取原始对象的属性，如果创立的对象比较复杂时，效率较低
  • 总是 须要从新初始化对象，而不是动静地取得对象运行时的状态, 不够灵便

改良的思路剖析

思路：Java 中 Object 类是所有类的根类，Object 类提供了一个 clone()办法.

该办法能够将一个 Java 对象复制一份，然而须要实现 clone 的 Java 类必须要实现一个接口 Cloneable，该接口示意该类可能复制且具备复制的能力 => 原型模式

class Sheep  implements Cloneable {
 
    // 省略要害代码....
 
    // 克隆该实例，应用默认的 clone 办法来实现
    @Override
    protected Object clone(){
        Sheep sheep = null;
        try {sheep = (Sheep) super.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();
        }
        return sheep;
    }
}

那么咱们是应用 demo 看看，与传统模式有何变动呢？

public static void main(String[] args) {
    // 传统的办法
    Sheep sheep = new Sheep("tom", 1, "红色");
    Sheep sheep2 = (Sheep)sheep.clone();
    Sheep sheep3 = (Sheep)sheep.clone();
    Sheep sheep4 = (Sheep)sheep.clone();
 
    //.........
}

咱们在应用原型模式的时候，克隆则就不无需每次 new 一个对象

并且如果 Sheep 办法，如何增加了一个字段属性，也会本人实现初始化

class Sheep  implements Cloneable {
 
    private String name;
 
    private int age;
 
    private String color;
    
    private String address;
 
 
    public Sheep(String name, int age, String color, String address) {
        this.name = name;
        this.age = age;
        this.color = color;
        this.address = address;
    }
 
    public String getAddress() {return address;}
 
    public void setAddress(String address) {this.address = address;}
}
public static void main(String[] args) {
    // 传统的办法
    Sheep sheep = new Sheep("tom", 1, "红色","内蒙古");
    Sheep sheep2 = (Sheep)sheep.clone();
    Sheep sheep3 = (Sheep)sheep.clone();
    Sheep sheep4 = (Sheep)sheep.clone();
 
    //.........
}

三、Spring 框架源码解析

Spring 中原型 bean 的创立，就是原型模式的利用

咱们应用一个类来举例说明一下

class Monster{
 
    private Integer id = 10;
 
    private String nickName = "牛魔王";
 
    private String skill = "芭蕉扇";
 
    public Monster() {System.out.println("monster 创立....");
    }
    
    public Monster(Integer id, String nickName, String skill) {
        this.id = id;
        this.nickName = nickName;
        this.skill = skill;
    }
 
    public Integer getId() {return id;}
 
    public void setId(Integer id) {this.id = id;}
 
    public String getNickName() {return nickName;}
 
    public void setNickName(String nickName) {this.nickName = nickName;}
 
    public String getSkill() {return skill;}
 
    public void setSkill(String skill) {this.skill = skill;}
}

同时咱们这里还有一个 bean 的 xml 文件配置

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:util="http://www.springframework.org/schema/util" 
    xmlns:task="http://www.springframework.org/schema/task"
    xsi:schemaLocation="
           http://www.springframework.org/schema/mvc
           http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
           http://www.springframework.org/schema/beans   
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           http://www.springframework.org/schema/context   
           http://www.springframework.org/schema/context/spring-context-3.0.xsd
           http://www.springframework.org/schema/util   
           http://www.springframework.org/schema/util/spring-util-3.0.xsd
           http://www.springframework.org/schema/task 
           http://www.springframework.org/schema/task/spring-task-3.2.xsd"<!-- 咱们这里的 scope="prototype" 即原型模式来创立 -->
        <bean id="id01" class="com.spring.bean.Monster" scope="prototype"/>
 
</beans>

接下来咱们应用 demo，测试原型模式下的 bean，获取对象是否相等

public static void main(String[] args) {ApplicationContext applicationContext = new ClassPathXmlApplicationContext("bean.xml");
    Object bean1 =applicationContext.getBean("id01");
    System.out.println("bean1 ="+bean1);
 
 
    Object bean2 =applicationContext.getBean("id01");
    System.out.println("bean2 ="+bean2);
 
    System.out.println(bean1 == bean2);
}
 
运行后果如下：monster 创立....
bean1=Monster{id=10,nickName='牛魔王', skill='芭蕉扇'}
monster 创立....
bean2=Monster{id=10,nickName='牛魔王', skill='芭蕉扇'}
false

阐明这两个对象，他的变量雷同，然而不是同一个对象，返回了 false

那么咱们须要晓得他是在哪里用到了原型呢？咱们 debug 看看

public abstract class AbstractApplicationContext extends DefaultResourceLoader implements ConfigurableApplicationContext, DisposableBean {
 
    // 省略其余要害代码....
    public Object getBean(String name) throws BeansException {return this.getBeanFactory().getBean(name);
    }
 
    public <T> T getBean(String name, Class<T> requiredType) throws BeansException {return this.getBeanFactory().getBean(name, requiredType);
    }
 
    public <T> T getBean(Class<T> requiredType) throws BeansException {return this.getBeanFactory().getBean(requiredType);
    }
 
    public Object getBean(String name, Object... args) throws BeansException {return this.getBeanFactory().getBean(name, args);
    }
 
    public boolean containsBean(String name) {return this.getBeanFactory().containsBean(name);
    }
 
    public boolean isSingleton(String name) throws NoSuchBeanDefinitionException {return this.getBeanFactory().isSingleton(name);
    }
 
    public boolean isPrototype(String name) throws NoSuchBeanDefinitionException {return this.getBeanFactory().isPrototype(name);
    }
}

咱们发现他是采纳 BeanFactory 里的 getBean，那么我进到外面去看

public abstract class AbstractRefreshableApplicationContext extends AbstractApplicationContext {
 
    // 省略其余要害代码....
    public final ConfigurableListableBeanFactory getBeanFactory() {synchronized(this.beanFactoryMonitor) {if (this.beanFactory == null) {throw new IllegalStateException("BeanFactory not initialized or already closed - call'refresh'before accessing beans via the ApplicationContext");
            } else {return this.beanFactory;}
        }
    }
}

返回工厂后，咱们就进 BeanFactory 的 getBean 办法里看看

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {
 
    
    // 省略其余要害代码....
    public AbstractBeanFactory() {}
 
    public AbstractBeanFactory(BeanFactory parentBeanFactory) {this.parentBeanFactory = parentBeanFactory;}
 
    public Object getBean(String name) throws BeansException {return this.doGetBean(name, (Class)null, (Object[])null, false);
    }
 
    public <T> T getBean(String name, Class<T> requiredType) throws BeansException {return this.doGetBean(name, requiredType, (Object[])null, false);
    }
 
    public Object getBean(String name, Object... args) throws BeansException {return this.doGetBean(name, (Class)null, args, false);
    }
 
    public <T> T getBean(String name, Class<T> requiredType, Object... args) throws BeansException {return this.doGetBean(name, requiredType, args, false);
    }    
}

发现是调用 doGetBean 办法，那咱们再进去 doGetBean 办法看看

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {
 
    
    // 省略其余要害代码....
    
    protected <T> T doGetBean(String name, Class<T> requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException {final String beanName = this.transformedBeanName(name);
        Object sharedInstance = this.getSingleton(beanName);
        Object bean;
        if (sharedInstance != null && args == null) {if (this.logger.isDebugEnabled()) {if (this.isSingletonCurrentlyInCreation(beanName)) {this.logger.debug("Returning eagerly cached instance of singleton bean'" + beanName + "'that is not fully initialized yet - a consequence of a circular reference");
                } else {this.logger.debug("Returning cached instance of singleton bean'" + beanName + "'");
                }
            }
 
            bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, (RootBeanDefinition)null);
        } else {if (this.isPrototypeCurrentlyInCreation(beanName)) {throw new BeanCurrentlyInCreationException(beanName);
            }
 
            BeanFactory parentBeanFactory = this.getParentBeanFactory();
            if (parentBeanFactory != null && !this.containsBeanDefinition(beanName)) {String nameToLookup = this.originalBeanName(name);
                if (args != null) {return parentBeanFactory.getBean(nameToLookup, args);
                }
 
                return parentBeanFactory.getBean(nameToLookup, requiredType);
            }
 
            if (!typeCheckOnly) {this.markBeanAsCreated(beanName);
            }
 
            try {final RootBeanDefinition mbd = this.getMergedLocalBeanDefinition(beanName);
                this.checkMergedBeanDefinition(mbd, beanName, args);
                String[] dependsOn = mbd.getDependsOn();
                String[] arr$;
                if (dependsOn != null) {
                    arr$ = dependsOn;
                    int len$ = dependsOn.length;
 
                    for(int i$ = 0; i$ < len$; ++i$) {String dependsOnBean = arr$[i$];
                        this.getBean(dependsOnBean);
                        this.registerDependentBean(dependsOnBean, beanName);
                    }
                }
 
                if (mbd.isSingleton()) {sharedInstance = this.getSingleton(beanName, new ObjectFactory<Object>() {public Object getObject() throws BeansException {
                            try {return AbstractBeanFactory.this.createBean(beanName, mbd, args);
                            } catch (BeansException var2) {AbstractBeanFactory.this.destroySingleton(beanName);
                                throw var2;
                            }
                        }
                    });
                    bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                } else if (mbd.isPrototype()) {
                    arr$ = null;
 
                    Object prototypeInstance;
                    try {this.beforePrototypeCreation(beanName);
                        prototypeInstance = this.createBean(beanName, mbd, args);
                    } finally {this.afterPrototypeCreation(beanName);
                    }
 
                    bean = this.getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
                } else {String scopeName = mbd.getScope();
                    Scope scope = (Scope)this.scopes.get(scopeName);
                    if (scope == null) {throw new IllegalStateException("No Scope registered for scope'" + scopeName + "'");
                    }
 
                    try {Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {public Object getObject() throws BeansException {AbstractBeanFactory.this.beforePrototypeCreation(beanName);
 
                                Object var1;
                                try {var1 = AbstractBeanFactory.this.createBean(beanName, mbd, args);
                                } finally {AbstractBeanFactory.this.afterPrototypeCreation(beanName);
                                }
 
                                return var1;
                            }
                        });
                        bean = this.getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                    } catch (IllegalStateException var21) {throw new BeanCreationException(beanName, "Scope'" + scopeName + "'is not active for the current thread;" + "consider defining a scoped proxy for this bean if you intend to refer to it from a singleton", var21);
                    }
                }
            } catch (BeansException var23) {this.cleanupAfterBeanCreationFailure(beanName);
                throw var23;
            }
        }
 
        if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
            try {return this.getTypeConverter().convertIfNecessary(bean, requiredType);
            } catch (TypeMismatchException var22) {if (this.logger.isDebugEnabled()) {this.logger.debug("Failed to convert bean'" + name + "'to required type [" + ClassUtils.getQualifiedName(requiredType) + "]", var22);
                }
 
                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
            }
        } else {return bean;}
    }
}

代码很多，我这里采纳图片的形式标注进去

对于在 spring 框架中原型模式，因为小编程度无限，暂且先理解这么多

四、浅拷贝和深拷贝

浅拷贝的介绍

对于数据类型是根本数据类型的成员变量，浅拷贝会间接进行值传递，也就是将该属性值复制一份给新的对象。

对于数据类型是援用数据类型的成员变量，比如说成员变量是某个数组、某个类的对象等，那么 浅拷贝会进行援用传递，也就是只是将该成员变量的援用值（内存地址）复制一份给新的对象。

为实际上两个对象的该成员变量都指向同一个实例。

在这种状况下，在一个对象中批改该成员变量会影响到另一个对象的该成员变量值

比如说之前克隆羊，咱们增加一个对象字段

class Sheep  implements Cloneable {
 
 
    // 省略其余关键性代码.....
 
    private Sheep friend;
    
    public Sheep(String name, int age, String color, String address, Sheep friend) {
        this.name = name;
        this.age = age;
        this.color = color;
        this.address = address;
        this.friend = friend;
    }
    
    public Sheep getFriend() {return friend;}
 
    public void setFriend(Sheep friend) {this.friend = friend;}
}

这时咱们创立 demo，一起看看领会援用拷贝地址指向新对象

public static void main(String[] args) {Sheep friend = new Sheep("jack", 2, "彩色","内蒙古");
        Sheep sheep = new Sheep("tom", 1, "红色","内蒙古",friend);
        Sheep sheep2 = (Sheep)sheep.clone();
        Sheep sheep3 = (Sheep)sheep.clone();
        Sheep sheep4 = (Sheep)sheep.clone();
        System.out.println(sheep2 + "hashCode"+sheep2.friend.hashCode());
        System.out.println(sheep3+ "hashCode"+sheep3.friend.hashCode());
        System.out.println(sheep4+ "hashCode"+sheep4.friend.hashCode());
    }
    
运行后果如下：Sheep{name='tom', age=1, color='红色', address=' 内蒙古}hashCode460141958
Sheep{name='tom', age=1, color='红色', address=' 内蒙古}hashCode460141958
Sheep{name='tom', age=1, color='红色', address=' 内蒙古}hashCode460141958

有没有发现，咱们输入好敌人的时候，都是指向同一个地址

这证实咱们没有真正的拷贝一个好敌人的对象，咱们称这为浅拷贝

浅拷贝是应用默认的 clone()办法来实现：就是 sheep = (Sheep) super.clone();

深拷贝根本介绍

复制对象的所有根本数据类型的成员变量值

为所有援用数据类型的成员变量申请存储空间，并复制每个援用数据类型成员变量所援用的对象，直到该对象可达的所有对象 。也就是说，对象进行深拷贝要对整个对象( 包含对象的援用类型 ) 进行拷贝

深拷贝实现形式 1：重写 clone 办法来实现深拷贝

深拷贝实现形式 2：通过对象序列化实现深拷贝(举荐)

咱们通过新的示例类来举例说明这两种状况

class DeepCloneableTarget implements Cloneable {
 
 
    public String name; //String 属 性
    public String cloneClass; //String 属 性
 
    public DeepCloneableTarget() {super();
    }
    
    public DeepCloneableTarget(String name, String cloneClass) {
        this.name = name;
        this.cloneClass = cloneClass;
    }
 
    public String getName() {return name;}
 
    public void setName(String name) {this.name = name;}
 
    public String getCloneClass() {return cloneClass;}
 
    public void setCloneClass(String cloneClass) {this.cloneClass = cloneClass;}
 
    @Override
    protected Object clone() throws CloneNotSupportedException {return super.clone();
    }
}

咱们应用默认的拷贝办法，当初咱们增加多一个类增加对象援用

class DeepProtoType implements  Cloneable {
 
    public String name; //String 属 性
    public DeepCloneableTarget deepCloneableTarget;// 援用类型
 
    public DeepProtoType() {}
 
    public DeepProtoType(String name, DeepCloneableTarget deepCloneableTarget) {
        this.name = name;
        this.deepCloneableTarget = deepCloneableTarget;
    }
 
    public String getName() {return name;}
 
    public void setName(String name) {this.name = name;}
 
    public DeepCloneableTarget getDeepCloneableTarget() {return deepCloneableTarget;}
 
    public void setDeepCloneableTarget(DeepCloneableTarget deepCloneableTarget) {this.deepCloneableTarget = deepCloneableTarget;}
}

那么咱们的第一种形式是：采纳重写 clone 办法来实现深拷贝

class DeepProtoType implements  Cloneable {
 
 
    // 省略其余要害代码....
    @Override
    protected Object clone() throws CloneNotSupportedException {
 
        // 实现对根本数据类型和 String 类型的拷贝
        Object deep = null;
        deep = super.clone();
 
        // 再实现对类里的援用类型拷贝
        DeepProtoType deepProtoType = (DeepProtoType)deep;
        deepProtoType.setDeepCloneableTarget((DeepCloneableTarget)deepCloneableTarget.clone());
 
        return deepProtoType;
    }
}

接下里咱们应用 demo 看看第一种形式的深拷贝成果怎么样？

public static void main(String[] args) {DeepCloneableTarget target = new DeepCloneableTarget("大牛", "大牛的类");
    DeepProtoType p1 = new DeepProtoType();
    p1.setName("小明");
    p1.setDeepCloneableTarget(target);
 
    try {
        // 形式 1  实现深拷贝
        DeepProtoType p2 = (DeepProtoType)p1.clone();
        System.out.println("p1.name =" + p1.name + "p1.deepCloneableTarget=" + p1.deepCloneableTarget.hashCode());
        System.out.println("p2.name =" + p1.name + "p2.deepCloneableTarget=" + p2.deepCloneableTarget.hashCode());
    } catch (CloneNotSupportedException e) {e.printStackTrace();
    }
}
 
运行后果如下：p1.name = 小明 p1.deepCloneableTarget=460141958
p2.name = 小明 p2.deepCloneableTarget=1163157884

这种形式采纳先拷贝根本数据类型再拷贝援用类型

1. 这种形式如果 DeepCloneableTarget 里也有援用类型的类，那么它也须要重写这个办法，这就会导致多重重写

2. 如果多个类的援用就会导致很繁琐，工作量微小，关系简单

论断：只适宜一层关系的援用，理论不太举荐

那么咱们的第二种形式是：通过对象序列化实现深拷贝(举荐)

应用序列化的形式，咱们须要实现 Serializable 接口

public class DeepProtoType implements Serializable, Cloneable{// 省略其余要害代码....}
 
 
public class DeepCloneableTarget implements Serializable, Cloneable{// 省略其余要害代码....}
public class DeepProtoType implements Serializable, Cloneable{
 
 
    // 省略其余要害代码....
    
    // 深拷贝 - 形式 2 通过对象的序列化实现 (举荐)
    public Object deepClone() {
 
        // 创立流对象
        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); // 以后这个对象以对象流的形式输入
 
            // 反序列化
            bis = new ByteArrayInputStream(bos.toByteArray());
            ois = new ObjectInputStream(bis);
            DeepProtoType copyObj = (DeepProtoType) ois.readObject();
            return copyObj;
        } catch (Exception e) {return null;} finally {
            // 敞开流
            try {bos.close();
                oos.close();
                bis.close();
                ois.close();} catch (Exception e2) {}}
    }
    
}

接下里咱们应用 demo 看看第二种形式的深拷贝成果怎么样？

public static void main(String[] args) {DeepCloneableTarget target = new DeepCloneableTarget("大牛", "小牛");
        DeepProtoType p1 = new DeepProtoType();
        p1.setName("小明");
        p1.setDeepCloneableTarget(target);
 
        // 形式 2  实现深拷贝
        DeepProtoType p2 = (DeepProtoType) p1.deepClone();
        System.out.println("p1.name =" + p1.name + "p1.deepCloneableTarget=" + p1.deepCloneableTarget.hashCode());
        System.out.println("p2.name =" + p1.name + "p2.deepCloneableTarget=" + p2.deepCloneableTarget.hashCode());
}
 
运行后果如下：p1.name = 小明 p1.deepCloneableTarget=1836019240
p2.name = 小明 p2.deepCloneableTarget=363771819

五、原型模式的注意事项和细节

创立新的对象 比较复杂时，能够 利用原型模式简化对象的创立过程，同时也可能提高效率

不必从新初始化对象，而是动静地取得对象运行时的状态

如果 原始对象发生变化(减少或者缩小属性)，其它克隆对象的也会产生相应的变动，无需批改代码

在实现深克隆的时候可能须要比较复杂的代码

毛病：须要为每一个类装备一个克隆办法，这对全新的类来说不是很难，但对已有的类进行革新时，须要批改其源代码，违反了 ocp 准则，这点请留神.

参考资料

尚硅谷：设计模式（韩顺平老师）：单例模式

Refactoring.Guru：《深刻设计模式》

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java
发表至： java
2021-01-12
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