Java Externalizable Example

Main.java

package com.hascode.sample;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.time.ZonedDateTime;

public class Main {

  public static void main(String[] args) throws Exception {
    User user = new User("Fred", ZonedDateTime.now());

    // serializing
    try (FileOutputStream fos = new FileOutputStream(
        "user.ser"); ObjectOutputStream outStream = new ObjectOutputStream(fos)) {
      System.out.printf("serializing user: %s\n", user);
      outStream.writeObject(user);
    }

    // deserializing
    try (FileInputStream fis = new FileInputStream(
        "user.ser"); ObjectInputStream in = new ObjectInputStream(fis)) {
      User user1 = (User) in.readObject();
      System.out.printf("deserialized user: %s\n", user1);
    }
  }
}

User.java

package com.hascode.sample;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.time.ZonedDateTime;

public class User implements Externalizable {

  private String name;
  private ZonedDateTime birthday;

  public User(){}
  public User(String name, ZonedDateTime birthday) {
    this.name = name;
    this.birthday = birthday;
  }

  public String getName() {
    return name;
  }

  public ZonedDateTime getBirthday() {
    return birthday;
  }

  @Override
  public String toString() {
    final StringBuilder sb = new StringBuilder("User{");
    sb.append("name='").append(name).append('\'');
    sb.append(", birthday=").append(birthday);
    sb.append('}');
    return sb.toString();
  }

  @Override
  public void writeExternal(ObjectOutput out) throws IOException {
    out.writeUTF(name);
    out.writeObject(birthday);
  }

  @Override
  public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
    this.name = in.readUTF();
    this.birthday = (ZonedDateTime) in.readObject();
  }
}