共计 12847 个字符，预计需要花费 33 分钟才能阅读完成。
前言
- 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：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：孙大圣插入猴毛，变出其余孙大圣
原型模式类图实例
- 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）
原型模式 java 代码实例
Sheep 类实现 Cloneable 接口重写 clone 办法
public class Sheep implements Cloneable{
private String name;
private int age;
private 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;}
@Override
public String toString() {
return "Sheep{" +
"name='" + name + '\'' +
", age=" + age +
", color='" + color + '\'' +
'}';
}
// 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 (Exception e) {System.out.println(e.getMessage());
}
return sheep;
}
}
Client 类测试创立多个 Sheep 的实例，查看是否状态统一。
public class Client {public static void main(String[] args) {System.out.println("原型模式实现对象的创立");
Sheep sheep=new Sheep("tom",1,"红色");
Sheep sheep2=(Sheep)sheep.clone();
Sheep sheep3=(Sheep)sheep.clone();
Sheep sheep4=(Sheep)sheep.clone();
System.out.println("sheep2:"+sheep2);
System.out.println("sheep3:"+sheep3);
System.out.println("sheep4:"+sheep4);
}
}
原型模式在 Spirng 框架中源码剖析
- Spring 中原型 Bean 的创立，就是原型模型的利用
- 代码剖析
ProtoType 类的测试用例
public class ProtoType {public static void main(String[] args) {ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
Object bean = applicationContext.getBean("id01");
System.out.println("bean" + bean);
Object bean2 = applicationContext.getBean("id01");
System.out.println(bean==bean2);
}
}
beans.xml 配置文件
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 这里咱们的 scope="prototype" 即 原型模式 -->
<bean id="id01" class="com.spring.bean.Monster" scope="prototype"></bean>
</beans>
追踪 applicationContext.getBean(“id01”)：进入 AbstractApplicationContext 类的 getBean 办法
//---------------------------------------------------------------------
// Implementation of BeanFactory interface
//---------------------------------------------------------------------
@Override
public Object getBean(String name) throws BeansException {assertBeanFactoryActive();
return getBeanFactory().getBean(name);
}
追踪 getBeanFactory(): 进入 AbstractRefreshableApplicationContext 类的 getBeanFactory（）办法
@Override
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");
}
return this.beanFactory;
}
}
追踪 getBean(): 进入 AbstractBeanFactory 类的 getBean()办法
@Override
public Object getBean(String name) throws BeansException {return doGetBean(name, null, null, false);
}
追踪 doGetBean(): 进入 doGetBean()办法
通过 if (mbd.isSingleton()) 和 else if (mbd.isPrototype())判断 scope 的作用域,
通过 createBean()创立一个原型模型，返回一个 bean。
/**
* Return an instance, which may be shared or independent, of the specified bean.
* @param name the name of the bean to retrieve
* @param requiredType the required type of the bean to retrieve
* @param args arguments to use when creating a bean instance using explicit arguments
* (only applied when creating a new instance as opposed to retrieving an existing one)
* @param typeCheckOnly whether the instance is obtained for a type check,
* not for actual use
* @return an instance of the bean
* @throws BeansException if the bean could not be created
*/
@SuppressWarnings("unchecked")
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {if (logger.isTraceEnabled()) {if (isSingletonCurrentlyInCreation(beanName)) {
logger.trace("Returning eagerly cached instance of singleton bean'" + beanName +
"'that is not fully initialized yet - a consequence of a circular reference");
}
else {logger.trace("Returning cached instance of singleton bean'" + beanName + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
if (isPrototypeCurrentlyInCreation(beanName)) {throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {return ((AbstractBeanFactory) parentBeanFactory).doGetBean(nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else if (requiredType != null) {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
else {return (T) parentBeanFactory.getBean(nameToLookup);
}
}
if (!typeCheckOnly) {markBeanAsCreated(beanName);
}
try {final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {for (String dep : dependsOn) {if (isDependent(beanName, dep)) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between'" + beanName + "'and'" + dep + "'");
}
registerDependentBean(dep, beanName);
try {getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'"+ beanName +"' depends on missing bean '"+ dep +"'", ex);
}
}
}
// Create bean instance.
if (mbd.isSingleton()) {sharedInstance = getSingleton(beanName, () -> {
try {return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {throw new IllegalStateException("No Scope registered for scope name'" + scopeName + "'");
}
try {Object scopedInstance = scope.get(beanName, () -> {beforePrototypeCreation(beanName);
try {return createBean(beanName, mbd, args);
}
finally {afterPrototypeCreation(beanName);
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
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",
ex);
}
}
}
catch (BeansException ex) {cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && !requiredType.isInstance(bean)) {
try {T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return convertedBean;
}
catch (TypeMismatchException ex) {if (logger.isTraceEnabled()) {
logger.trace("Failed to convert bean'" + name + "'to required type'" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
浅拷贝
- 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，某个类型的对象等，那么浅拷贝会进行援用传递，也就是只是该成员变量的援用值（内存地址）复制一份给新的对象，因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。
- 克隆羊的案例就是浅拷贝
- 浅拷贝是应用默认的 clone（）办法来实现 sheep=（Sheep）super。clone（）；
浅拷贝代码实例：
在原有的 Sheep 类根底上增加 public Sheep friend;
public class Sheep implements Cloneable{
private String name;
private int age;
private String color;
private String address="蒙古羊";
public Sheep friend;
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;}
@Override
public String toString() {
return "Sheep{" +
"name='" + name + '\'' +
", age=" + age +
", color='" + color + '\'' +
'}';
}
// 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 (Exception e) {System.out.println(e.getMessage());
}
return sheep;
}
}
编写 Client 的测试用例，打印 sheep.friend 的 hashCode 值，察看它是否产生了新的对象。
public class Client {public static void main(String[] args) {System.out.println("原型模式实现对象的创立");
Sheep sheep = new Sheep("tom", 1, "红色");
sheep.friend=new Sheep("jack",2,"彩色");
Sheep sheep2 = (Sheep) sheep.clone();
Sheep sheep3 = (Sheep) sheep.clone();
Sheep sheep4 = (Sheep) sheep.clone();
System.out.println("sheep2:" + sheep2+"sheep.friend2="+sheep2.friend.hashCode());
System.out.println("sheep3:" + sheep3+"sheep.friend3="+sheep3.friend.hashCode());
System.out.println("sheep4:" + sheep4+"sheep.friend4="+sheep4.friend.hashCode());
}
}
根本介绍
- 复制对象的所有根本数据类型的成员变量值
- 为所有的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，晓得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进行拷贝
- 深拷贝实现形式一：重写 clone 办法来实现深拷贝
- 深拷贝实现形式二：通过对象序列化来实现深拷贝
深拷贝代码实例：
形式一：重写 clone 办法
DeepCloneableTarget 类
public class DeepCloneableTarget implements Serializable, Cloneable {
private static final long serialVersionUID = 1L;
private String cloneName;
private String cloneClass;
public DeepCloneableTarget(String cloneName, String cloneClass) {
this.cloneName = cloneName;
this.cloneClass = cloneClass;
}
// 因为该类的属性，都是 String，因而咱们这里应用默认的 clone 实现即可.
@Override
protected Object clone() throws CloneNotSupportedException {return super.clone();
}
}
DeepProtoType 类
public class DeepProtoType implements Serializable, Cloneable {
public String name;
public DeepCloneableTarget deepCloneableTarget;
public DeepProtoType() {super();
}
// 深拷贝 - 形式 1 应用 clone 办法
@Override
protected Object clone() throws CloneNotSupportedException {
Object deep = null;
// 实现对根本数据类型（属性）和 String 的克隆
deep = super.clone();
// 对援用类型的属性，进行独自的解决。DeepProtoType deepProtoType = (DeepProtoType) deep;
deepProtoType.deepCloneableTarget = (DeepCloneableTarget) deepCloneableTarget.clone();
return deep;
}
}
测试用例：Client
public class Client {public static void main(String[] args) throws Exception{DeepProtoType p = new DeepProtoType();
p.name="宋江";
p.deepCloneableTarget=new DeepCloneableTarget("大牛","小牛的");
// 形式 1 实现深拷贝
DeepProtoType p2=(DeepProtoType)p.clone();
System.out.println("p.name="+p.name+"p.deepCloneableTarget="+p.deepCloneableTarget.hashCode());
System.out.println("p2.name="+p2.name+"p.deepCloneableTarget="+p2.deepCloneableTarget.hashCode());
}
}
形式二：通过对象序列化来实现深拷贝（举荐应用）
DeepCloneableTarget 类
public class DeepCloneableTarget implements Serializable, Cloneable {
private static final long serialVersionUID = 1L;
private String cloneName;
private String cloneClass;
public DeepCloneableTarget(String cloneName, String cloneClass) {
this.cloneName = cloneName;
this.cloneClass = cloneClass;
}
// 因为该类的属性，都是 String，因而咱们这里应用默认的 clone 实现即可.
@Override
protected Object clone() throws CloneNotSupportedException {return super.clone();
}
}
DeepProtoType 类
public class DeepProtoType implements Serializable, Cloneable {
public String name;
public DeepCloneableTarget deepCloneableTarget;
public DeepProtoType() {super();
}
// 深拷贝 - 形式 2 通过对象序列化实现（举荐应用）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) {e.printStackTrace();
return null;
} finally {
try {bos.close();
oos.close();
bis.close();
ois.close();} catch (Exception e2) {e2.printStackTrace();
}
}
}
}
Client 测试用例
public class Client {public static void main(String[] args) throws Exception {DeepProtoType p = new DeepProtoType();
p.name = "宋江";
p.deepCloneableTarget = new DeepCloneableTarget("大牛", "小牛的");
// 形式 2 实现深拷贝
DeepProtoType p3=(DeepProtoType) p.deepClone();
System.out.println("p.name=" + p.name + "p.deepCloneableTarget=" + p.deepCloneableTarget.hashCode());
System.out.println("p3.name=" + p3.name + "p.deepCloneableTarget=" + p3.deepCloneableTarget.hashCode());
}
}
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
- 如果院士对象发生变化（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。
最初
感激你看到这里，看完有什么的不懂的能够在评论区问我，感觉文章对你有帮忙的话记得给我点个赞，每天都会分享 java 相干技术文章或行业资讯，欢送大家关注和转发文章！
正文完
