原型模式（Prototype Pattern）

拼搏现实的明天。 2022-06-16 11:11 244阅读 0赞

原型模式的定义：

Specify the kinds of objects to create using a prototypical instance , and create new objects by copying this prototype .

使用原型实例指定要创建的对象类型，通过复制这个实例创建新的对象。

原型模式在生活中的应用场景：

假如你刚给自己的客厅做了装修，你朋友正好也希望给他的客厅做装修，那么，他可能把你家的装修方案拿过来改改就成，你的装修方案就是原型。

原型模式的实现：

提供一个静态工厂方法来获得原型数据，然后复制这些数据，最后做相应的初始化。为了操作安全，我们不直接使用原型数据，而是使用clone()方法从内存中克隆这条原型数据再做后续操作。在这里使用的是Java提供java.lang.Cloneable接口克隆数据。

（我们在复制新的新的数据时，需要特别注意的是，我们不能把所有数据都复制过来，例如，当对象包含主键时，不能使用原型数据的主键，必须创建一个新的主键。）

package com.alex.prototypepattern;
    
    public class PackageInfoTestDrive {
        public static void main(String[] args) {
            PackageInfo currentInfo = PackageInfo.clonePackage("John");
            System.out.println("Original package information:");
            display(currentInfo);
    
            currentInfo.setId(10000l);
            currentInfo.setReceiverName("Ryan");
            currentInfo.setReceiverAddress("People Square, Shanghai");
    
            System.out.println("\nNew package information:");
            display(currentInfo);
        }
    
        private static void display(PackageInfo currentInfo) {
            System.out.println("Package id: " + currentInfo.getId());
            System.out.println("Receiver name: " + currentInfo.getReceiverName());
            System.out.println("Receiver address: " + currentInfo.getReceiverAddress());
            System.out.println("Sender name: " + currentInfo.getSenderName());
            System.out.println("Sender Phone No.: " + currentInfo.getSenderPhoneNo());
        }
    }

package com.alex.prototypepattern;
    
    
    public class PackageInfo implements Cloneable{
    	 private Long id;
    	    private String receiverName;
    	    private String receiverAddress;
    	    private String senderName;
    	    private String senderPhoneNo;
    
    	    //other fields, getters, setters and other methods...
    
    
    	    public Long getId() {
    	        return id;
    	    }
    
    	    public void setId(Long id) {
    	        this.id = id;
    	    }
    
    	    public String getReceiverName() {
    	        return receiverName;
    	    }
    
    	    public void setReceiverName(String receiverName) {
    	        this.receiverName = receiverName;
    	    }
    
    	    public String getReceiverAddress() {
    	        return receiverAddress;
    	    }
    
    	    public void setReceiverAddress(String receiverAddress) {
    	        this.receiverAddress = receiverAddress;
    	    }
    
    	    public String getSenderName() {
    	        return senderName;
    	    }
    
    	    public void setSenderName(String senderName) {
    	        this.senderName = senderName;
    	    }
    
    	    public String getSenderPhoneNo() {
    	        return senderPhoneNo;
    	    }
    
    	    public void setSenderPhoneNo(String senderPhoneNo) {
    	        this.senderPhoneNo = senderPhoneNo;
    	    }
    	    
    	public PackageInfo clone(){
    		try{
    			return (PackageInfo)super.clone();
    		}catch(CloneNotSupportedException ex){
    			System.out.println("Cloning not allowed");
    			return null;
    		}
    	}
    	
    	public static PackageInfo clonePackage(String userName){
    		PackageInfo prototype = loadPackageInfo(userName);
    		prototype.clone();
    		prototype.setId(null);
    		return prototype;
    	}
    	
    	 //Simulate loading data from database
        private static PackageInfo loadPackageInfo(String userName) {
            PackageInfo packageInfo = new PackageInfo();
    
            //create a String object in jvm heap not jvm string pool
            packageInfo.setId(100l);
            packageInfo.setReceiverName("John");
            packageInfo.setReceiverAddress("People Square,Shanghai");
            packageInfo.setSenderName("William");
            packageInfo.setSenderPhoneNo("12345678901");
            return packageInfo;
        }
    }

运行结果：

Original package information:  
Package id: null  
Receiver name: John  
Receiver address: People Square,Shanghai  
Sender name: William  
Sender Phone No.: 12345678901  
  
  
New package information:  
Package id: 10000  
Receiver name: Ryan  
Receiver address: People Square, Shanghai  
Sender name: William  
Sender Phone No.: 12345678901

Object 的 clone()方法的复制是采用逐字节的方式从内存复制数据，复制了对象属性的引用，而属性所指的对象本身没有复制，因此所复制的引用指向了相同的对象。用这种方式复制对象是浅拷贝，不是深拷贝。

注：本文大部分内容点来自刘济华的《漫谈设计模式》