原型模式
原型模式
基本介绍
- 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：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：孙大圣拔出猴毛，变出其他孙大圣
原型模式类图实例
- 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）
原型模式java代码实例
Sheep类实现Cloneable接口重写clone方法
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，使用默认的clone方法来完成
@Override
protected Object clone() {
Sheep sheep = null;
try {
sheep = (Sheep) super.clone();
} catch (Exception e) {
System.out.println(e.getMessage());
}
return sheep;
}
}
Client类测试创建多个Sheep的实例，查看是否状态一致。
public class Client {
public static void main(String[] args) {
System.out.println("原型模式完成对象的创建");
Sheep sheep=new Sheep("tom",1,"白色");
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框架中源码分析
- Spring中原型Bean的创建，就是原型模型的应用
- 代码分析
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">
<!-- 这里我们的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方法
//---------------------------------------------------------------------
// 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（）方法
@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()方法
@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
追踪doGetBean():进入doGetBean()方法
通过if (mbd.isSingleton()) 和else if (mbd.isPrototype())判断scope的作用域,
通过createBean()创建一个原型模型，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
基本介绍
- 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，某个类型的对象等，那么浅拷贝会进行引用传递，也就是只是该成员变量的引用值（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。
- 克隆羊的案例就是浅拷贝
- 浅拷贝是使用默认的clone（）方法来实现sheep=（Sheep）super。clone（）；
浅拷贝代码实例：
在原有的Sheep类基础上添加 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，使用默认的clone方法来完成
@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，观察它是否产生了新的对象。
public class Client {
public static void main(String[] args) {
System.out.println("原型模式完成对象的创建");
Sheep sheep = new Sheep("tom", 1, "白色");
sheep.friend=new Sheep("jack",2,"黑色");
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());
}
}
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
- 为所有的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，知道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
- 深拷贝实现方式一：重写clone方法来实现深拷贝
- 深拷贝实现方式二：通过对象序列化来实现深拷贝
深拷贝代码实例：
方式一：重写clone方法
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，因此我们这里使用默认的clone完成即可.
@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 - 方式1 使用clone 方法
@Override
protected Object clone() throws CloneNotSupportedException {
Object deep = null;
//完成对基本数据类型（属性）和String的克隆
deep = super.clone();
//对引用类型的属性，进行单独的处理。
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");
//方式1 完成深拷贝
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());
}
}
方式二：通过对象序列化来实现深拷贝（推荐使用）
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，因此我们这里使用默认的clone完成即可.
@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 - 方式2 通过对象序列化实现（推荐使用）
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) {
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");
//方式2 完成深拷贝
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
- 如果院士对象发生变化（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。
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