Note-序列化时readObjectNoData的使用

今天在sf上看到关于java序列化的一个方法,作用问题。
readObjectNoData>>问题链接

不明所以然，于是google了下。
后来题主给了我一个链接才看懂。于是自己试了一下，这里做一下记录。

这里有stackoverflown的一个相关问题，不过都是英文，但是其中一个回答，在我看了上面一个链接用例之后，结合这个就看懂了。

"Extendable" means "can have a subclass".

readObjectNoData is used in an unusual case where the serializer (writer) is working with a version of a class with no base class, whereas the deserializer (reader) of the class has a version of the class that IS based on a subclass. The subclass can say "it's ok if my base class isn't in the serialized data - just make an empty one" by implementing readObjectNoData. See theserelease notes.

还是修改后的代码：

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
public class SerializeTest {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
         Persons p = new Persons(); 
         p.setAge(10);             
         ObjectOutputStream oos;
        try {
        //先对旧的类对象进行序列化
        oos = new ObjectOutputStream(new FileOutputStream("./person.ser"));
            oos.writeObject(p);            
            oos.flush();             
            oos.close();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }             
    }
}
class Persons implements Serializable { 
        private int age;                
        public Persons() {}              
        public void setAge(int age){
            this.age = age;
        }
        public int getAge(){
            return this.age;
        }
}

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class SerializeTest {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
         Persons p = new Persons();             
         p.setAge(10);             
         ObjectOutputStream oos;
        try {
        //用新的类规范来反序列化
         ObjectInputStream ois = new ObjectInputStream(new FileInputStream("./person.ser"));       
              Persons sp = (Persons) ois.readObject();       
              System.out.println(sp.getName());
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }             
    }
}
//新的类继承了animals，这是已经序列化的旧对象里面所没有的内容，
//所以实现readObjectNoData，可以弥补这种因临时扩展而无法兼容反序列化的缺陷
 class Persons extends Animals  implements Serializable {
                private int age; 
                public Persons() {  } 
                public void setAge(int age){
                    this.age = age;
                }
                public int getAge(){
                    return this.age;
                }
            }

class Animals implements Serializable {  
            private String name; 
            public Animals() {  } 
            public void setName(String name){
                this.name = name;
            }          
            public String getName(){
                return this.name;
            }
            private void readObjectNoData() {
                this.name = "zhangsan";                 
            }          
}