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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》
正文完
