Java Serializable example

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

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

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 a User instance to the file system:

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 a User instance from the file system:

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

Let's create a simple test class:

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:

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

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