深度分析:java设计模式中的原型模式,看完就没有说不懂的

前程有光

前言

  1. 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
  2. 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。
  3. 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()
  4. 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

  1. Prototype:原型类,声明一个克隆自己的接口
  2. ConcretePrototype:具体的原型类,实现一个克隆自己的操作。
  3. 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

  1. Spring中原型Bean的创建,就是原型模型的应用
  2. 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

  1. 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。
  2. 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。
  3. 克隆羊的案例就是浅拷贝
  4. 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());
    }
}

基本介绍

  1. 复制对象的所有基本数据类型的成员变量值
  2. 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
  3. 深拷贝实现方式一:重写clone方法来实现深拷贝
  4. 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

  1. 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
  2. 不用重新初始化对象,而是动态地获得对象运行时的状态
  3. 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。
  4. 在实现深克隆的时候可能需要比较复杂的代码
  5. 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。

最后

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