java Externalizable interface demo

ExternalizableDemo.java

import java.io.*;

/**
 * reference link
 * https://mp.weixin.qq.com/s/QS9e_lVxr5vuphql5O3xhA
 * https://www.cnblogs.com/chenfei0801/archive/2013/04/06/3002146.html
 * 对一个实现了Externalizable接口的类进行序列化及反序列化
 */
public class ExternalizableDemo1 {

    public static void main(String[] args) {
        //Write Obj to file
        User1 user = new User1();
        user.setName("hollis");
        user.setAge(23);
        try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("tempFile"))) {
            oos.writeObject(user);
        } catch (IOException e) {
            e.printStackTrace();
        }

        //Read Obj from file
        File file = new File("tempFile");
        try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file))) {
            User1 newInstance = (User1) ois.readObject();
            //output
            System.out.println(newInstance);
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}
//OutPut:
//User{name='null', age=0}

//在writeExternal readExternal 写入相关代码后发现有值了
//我觉得write 和 read 必须按顺序来，什么顺序write 就什么顺序 read
//Externalizable这个可以控制某些字段序列化时不输入值，或者某些字段可以输出值，也可以使用 transient 关键字来实现
//Externalizable 相比 Serializable接口更加的可控，更加的灵活


class User1 implements Externalizable {

    private String name;
    private int age;

    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 void writeExternal(ObjectOutput out) throws IOException {
        System.out.println("invoke writeExtenal???");
        out.writeObject(name);//原本是不输入值的，加了这个之后读时就会读出来，
        out.writeInt(age);
    }

    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        System.out.println("invoke readExtenal???");
        name = (String) in.readObject();// 原本是不输出值的，现在有值了
        age = in.readInt();
    }

    public User1() {
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}