【原型模式】

news/2024/9/19 0:41:46/ 标签: 原型模式

原型模式 Prototype Pattern

属于创建型模式
是指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，调用者不需要知道任何创建细节，不调用构造函数
关键点：不通过 new 关键字，而是通过方法去创建对象

原型模式的使用场景

类初始化消耗资源较多
new 产生的一个对象需要非常繁琐的过程（数据准备、访问权限等）
构造函数比较复杂
循环体中生产大量对象

通过硬编码复制对象

编写比较麻烦

@Data
public class User {private Long id;private String name;private String pwd;private String addr;private String mobile;private int age;// ... 属性非常多 .../*** 硬编码复制*/public User copy() {User user = new User();user.setId(this.getId());user.setName(this.getName());user.setPwd(this.getPwd());user.setAddr(this.getAddr());user.setMobile(this.getMobile());user.setAge(this.getAge());// ...这里还有很多属性set...return user;}}

通过反射复制对象

本质也是 set、get

public static Object copy(Object prototype) {Class<?> clazz = prototype.getClass();Object returnValue;try {returnValue = clazz.newInstance();// 获取所有属性, 并设置可访问for (Field field : clazz.getDeclaredFields()) {field.setAccessible(true);field.set(returnValue, field.get(prototype));}} catch (Exception e) {throw new RuntimeException(e);}return returnValue;
}

浅拷贝复制对象

浅拷贝的特点

对于基本类型是按值复制，不会因为原对象的基本类型值的改变而影响到拷贝后的对象
对于引用类型，prototype 和 clone 对象引用同一个引用类型对象（复制引用对象的内存地址）

浅拷贝存在的问题

修改 clone[prototype] 引用的对象后，会影响到 prototype[clone]

@Data
public class ConcretePrototype implements Cloneable {private String name;private int age;private List<String> hobbies;/*** 实现 Cloneable 接口, 底层使用字节码进行克隆*/@Overridepublic ConcretePrototype clone() {try {// TODO: copy mutable state here, so the clone can't change the internals of the originalreturn (ConcretePrototype) super.clone();} catch (CloneNotSupportedException e) {throw new AssertionError();}}
}

测试及结果
修改 prototype 的 hobbies 后，clone 的 hobbies 也被修改了

public static void main(String[] args) {ShallowConcretePrototype prototype = new ShallowConcretePrototype();prototype.setAge(20);prototype.setName("yes");ArrayList<String> hobbies = new ArrayList<>();hobbies.add("书法");hobbies.add("象棋");prototype.setHobbies(hobbies);ShallowConcretePrototype clone = prototype.clone();System.out.println("prototype == clone : " + (prototype == clone));prototype.setAge(25);System.out.println("==== 修改基本类型 age ====");System.out.println(prototype);System.out.println(clone);prototype.hobbies.add("游戏");System.out.println("prototype.hobbies == clone.hobbies : " + (prototype.hobbies == clone.hobbies));System.out.println("==== 修改引用类型 hobbies ====");System.out.println(prototype.hobbies);System.out.println(clone.hobbies);System.out.println("prototype.hobbies == clone.hobbies : " + (prototype.hobbies == clone.hobbies));
}

流实现深拷贝复制对象

@Data
public class DeepConcretePrototype implements Serializable
, Cloneable {private String name;private int age;private List<String> hobbies;@Overridepublic DeepConcretePrototype clone(){try {ByteArrayOutputStream bos = new ByteArrayOutputStream();ObjectOutputStream oos = new ObjectOutputStream(bos);oos.writeObject(this);ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());ObjectInputStream ois = new ObjectInputStream(bis);return (DeepConcretePrototype)ois.readObject();} catch (Exception e) {throw new RuntimeException(e);}}
}

测试及结果

public static void main(String[] args) {DeepConcretePrototype prototype = new DeepConcretePrototype();prototype.setAge(20);prototype.setName("yes");ArrayList<String> hobbies = new ArrayList<>();hobbies.add("书法");hobbies.add("象棋");prototype.setHobbies(hobbies);DeepConcretePrototype clone = prototype.clone();System.out.println("prototype == clone : " + (prototype == clone));prototype.setAge(25);System.out.println("==== 修改基本类型 age ====");System.out.println(prototype);System.out.println(clone);prototype.hobbies.add("游戏");System.out.println("prototype.hobbies == clone.hobbies : " + (prototype.hobbies == clone.hobbies));System.out.println("==== 修改引用类型 hobbies ====");System.out.println(prototype.hobbies);System.out.println(clone.hobbies);System.out.println("prototype.hobbies == clone.hobbies : " + (prototype.hobbies == clone.hobbies));
}