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我所知道设计模式之原型模式

互联网 diligentman 3天前 7次浏览

前言需求


接下里介绍的是Java 的设计模式之一:原型模式

现在有一只羊 tom

姓名为: tom, 年龄为:1,颜色为:白色

请编写程序创建和 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种类,并且通过拷贝这些原型,创建新的对象

原型模式是一种创建型设计模式允许一个对象再创建另外一个可定制的对象,无需知道如何创建的细节

工作原理是:通过将一个原型对象传给那个要发动创建的对象,这个要发动创建的对象通过请求原型对象拷贝它们自己来实施创建,即对象.clone()

形象的理解:齐天大圣孙悟空拔出猴毛, 变出其它孙大圣

我所知道设计模式之原型模式

原理结构图说明
Prototype : 原型类,声明一个克隆自己的接口
ConcretePrototype: 具体的原型类, 实现一个克隆自己的操作
Client: 让一个原型对象克隆自己,从而创建一个新的对象(属性一样)

我所知道设计模式之原型模式

二、通过示例说明情况

我们按照传统方式解决之前提出的克隆羊问题

我所知道设计模式之原型模式

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;
    }
}

我们生成一只羊,然后根据这只羊的属性创建十只羊

public static void main(String[] args) {
        //传统的方法
        Sheep sheep = new Sheep("tom", 1, "白色");
        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());
        
        //.........
    }
传统的方式的优缺点
  • 优点是比较好理解,简单易操作
  • 创建新的对象时,总是需要重新获取原始对象的属性,如果创建的对象比较复杂时,效率较低
  • 总是需要重新初始化对象,而不是动态地获得对象运行时的状态, 不够灵活
改进的思路分析

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

该方法可以将一个 Java 对象复制一份,但是需要实现 clone 的Java 类必须要实现一个接口 Cloneable,该接口表示该类能够复制且具有复制的能力 =>原型模式

class Sheep  implements Cloneable {

    //省略关键代码....

    //克隆该实例,使用默认的clone方法来完成
    @Override
    protected Object clone(){
        Sheep sheep = null;
        try {
            sheep = (Sheep) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return sheep;
    }
}

那么我们是使用demo看看,与传统模式有何变化呢?

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

    //.........
}

我们在使用原型模式的时候,克隆则就不无需每次new一个对象

并且如果Sheep方法,如何添加了一个字段属性,也会自己完成初始化

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) {
    //传统的方法
    Sheep sheep = new Sheep("tom", 1, "白色","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 的创建,就是原型模式的应用

我们使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 创建....");
    }
    
    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;
    }
}

同时我们这里还有一个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"
        
        <!--我们这里的scope="prototype" 即原型模式来创建-->
        <bean id="id01" class="com.spring.bean.Monster" scope="prototype"/>

</beans>

接下来我们使用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);
}

运行结果如下:
monster 创建....
bean1=Monster{id=10,nickName='牛魔王', skill='芭蕉扇'}
monster 创建....
bean2=Monster{id=10,nickName='牛魔王', skill='芭蕉扇'}
false

说明这两个对象,他的变量相同,但是不是同一个对象,返回了false

那么我们需要知道他是在哪里用到了原型呢?我们debug看看

public abstract class AbstractApplicationContext extends DefaultResourceLoader implements ConfigurableApplicationContext, DisposableBean {

    //省略其他关键代码....
    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);
    }
}

我们发现他是采用BeanFactory里的getBean,那么我进到里面去看

public abstract class AbstractRefreshableApplicationContext extends AbstractApplicationContext {

    //省略其他关键代码....
    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,我们就进BeanFactory的getBean方法里看看

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {

    
    //省略其他关键代码....
    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方法,那我们再进去doGetBean方法看看

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {

    
    //省略其他关键代码....
    
    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,我这里采用图片的方式标注出来

我所知道设计模式之原型模式

关于在spring框架中原型模式,由于小编水平有限,暂且先了解这么多

四、浅拷贝和深拷贝

浅拷贝的介绍

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

对于数据类型是引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,那么浅拷贝会进行引用传递,也就是只是将该成员变量的引用值(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。

在这种情况下,在一个对象中修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,我们添加一个对象字段

class Sheep  implements Cloneable {


    //省略其他关键性代码.....

    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;
    }
}

这时我们创建demo ,一起看看体会引用拷贝地址指向新对象

public static void main(String[] args) {

        Sheep friend = new Sheep("jack", 2, "黑色","内蒙古");
        Sheep sheep = new Sheep("tom", 1, "白色","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());
    }
    
运行结果如下:
Sheep{name='tom', age=1, color='白色', address='内蒙古}hashCode460141958
Sheep{name='tom', age=1, color='白色', address='内蒙古}hashCode460141958
Sheep{name='tom', age=1, color='白色', address='内蒙古}hashCode460141958

有没有发现,我们输出好朋友的时候,都是指向同一个地址

我所知道设计模式之原型模式

这证明我们没有真正的拷贝一个好朋友的对象,我们称这为浅拷贝

浅拷贝是使用默认的 clone()方法来实现:就是sheep = (Sheep) super.clone();

深拷贝基本介绍

复制对象的所有基本数据类型的成员变量值

为所有引用数据类型的成员变量申请存储空间,并复制每个引用数据类型成员变量所引用的对象,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(包括对象的引用类型)进行拷贝

深拷贝实现方式 1:重写 clone 方法来实现深拷贝

深拷贝实现方式 2:通过对象序列化实现深拷贝(推荐)

我们通过新的示例类来举例说明这两种情况

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();
    }
}

我们使用默认的拷贝方法,现在我们添加多一个类添加对象引用

class DeepProtoType implements  Cloneable {

    public String name; //String 属 性
    public DeepCloneableTarget deepCloneableTarget;// 引用类型

    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;
    }
}

那么我们的第一种方式是:采用重写 clone 方法来实现深拷贝

class DeepProtoType implements  Cloneable {


    //省略其他关键代码....
    @Override
    protected Object clone() throws CloneNotSupportedException {

        //完成对基本数据类型和String类型的拷贝
        Object deep = null;
        deep = super.clone();

        //再完成对类里的引用类型拷贝
        DeepProtoType deepProtoType = (DeepProtoType)deep;
        deepProtoType.setDeepCloneableTarget((DeepCloneableTarget)deepCloneableTarget.clone());

        return deepProtoType;
    }
}

接下里我们使用demo 看看第一种方式的深拷贝效果怎么样?

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 {
        //方式 1  完成深拷贝
        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();
    }
}

运行结果如下:
p1.name = 小明 p1.deepCloneableTarget=460141958
p2.name = 小明 p2.deepCloneableTarget=1163157884

这种方式采用先拷贝基本数据类型再拷贝引用类型

1.这种方式如果DeepCloneableTarget里也有引用类型的类,那么它也需要重写这个方法,这就会导致多重重写

2.如果多个类的引用就会导致很繁琐,工作量巨大,关系复杂

结论:只适合一层关系的引用,实际不太推荐

那么我们的第二种方式是:通过对象序列化实现深拷贝(推荐)

使用序列化的方式,我们需要实现Serializable接口

public class DeepProtoType implements Serializable, Cloneable{
    
    //省略其他关键代码....
}


public class DeepCloneableTarget implements Serializable, Cloneable{

    //省略其他关键代码....
}
public class DeepProtoType implements Serializable, Cloneable{


    //省略其他关键代码....
    
    //深拷贝 - 方式 2 通过对象的序列化实现 (推荐)
    public Object deepClone() {

        //创建流对象
        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); //当前这个对象以对象流的方式输出

            //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 {
            //关闭流
            try {
                bos.close();
                oos.close();
                bis.close();
                ois.close();
            } catch (Exception e2) {
            }
        }
    }
    
}

接下里我们使用demo 看看第二种方式的深拷贝效果怎么样?

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);

        //方式 2  完成深拷贝
        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());
}

运行结果如下:
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

创建新的对象比较复杂时,可以利用原型模式简化对象的创建过程,同时也能够提高效率

不用重新初始化对象,而是动态地获得对象运行时的状态

如果原始对象发生变化(增加或者减少属性),其它克隆对象的也会发生相应的变化,无需修改代码

在实现深克隆的时候可能需要比较复杂的代码

缺点:需要为每一个类配备一个克隆方法,这对全新的类来说不是很难,但对已有的类进行改造时,需要修改其源代码,违背了 ocp 原则,这点请注意.

参考资料


尚硅谷:设计模式(韩顺平老师):单例模式

Refactoring.Guru:《深入设计模式


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