Java Serializable example

15 January 2013
By Gonçalo Marques
In this tutorial you will learn how to serialize a Java object to the file system and read it afterwards.

Introduction

This tutorial will demonstrate how to serialize a Java object to the file system. After serialization we will read it again into memory.

Environment:

  1. Ubuntu 12.04
  2. JDK 1.7.0.09

A simple class

Let's define a simple class to use in this example:

User class

package com.byteslounge.serialization;

import java.io.Serializable;

public class User implements Serializable {

  private static final long serialVersionUID = -388040256197985515L;
  
  private int id;
  private String username;
  private String email;
  
  public User(int id, String username, String email) {
    this.id = id;
    this.username = username;
    this.email = email;
  }

  public int getId() {
    return id;
  }

  public String getUsername() {
    return username;
  }

  public String getEmail() {
    return email;
  }
  
}

Note that we are implementing the Serializable interface. This is required to make User class serializable.

Serializing

Serializing a User instance to the file system:

Serializing

User userWrite = new User(1, "johndoe", "John Doe");
FileOutputStream fos = new FileOutputStream("testfile");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(userWrite);
oos.flush();
oos.close();

Deserializing

Deserializing a User instance from the file system:

Deserializing

User userRead;
FileInputStream fis = new FileInputStream("testfile");
ObjectInputStream ois = new ObjectInputStream(fis);
userRead = (User)ois.readObject();
ois.close();

Testing

Let's create a simple test class:

Main.java

package com.byteslounge.serialization;

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

public class Main {

  public static void main(String[] args) 
    throws Exception {
    
    User userWrite = new User(1, "johndoe", "John Doe");
    FileOutputStream fos = new FileOutputStream("testfile");
    ObjectOutputStream oos = new ObjectOutputStream(fos);
    oos.writeObject(userWrite);
    oos.flush();
    oos.close();

    User userRead;
    FileInputStream fis = new FileInputStream("testfile");
    ObjectInputStream ois = new ObjectInputStream(fis);
    userRead = (User)ois.readObject();
    ois.close();
    
    System.out.println("username: " + userRead.getUsername());

  }

}

When we run the test the following output is generated:

username: johndoe

The example source code is available at the end of this page.

Download source code from this article

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About the author
Gonçalo Marques is a Software Engineer with several years of experience in software development and architecture definition. During this period his main focus was delivering software solutions in banking, telecommunications and governmental areas. He created the Bytes Lounge website with one ultimate goal: share his knowledge with the software development community. His main area of expertise is Java and open source.

GitHub profile: http://github.com/gonmarques

He is also the author of the WiFi File Browser Android application: