Overview

Java serialization is a process of writing the state of the object into a writable byte stream. Serializable classes can be written to a file on your computer. The reverse process of serialization is called de-serialization. i.e restoring the state of the object from the byte stream.

 

Serialization and De-serialization

Serializabilition of a class is enabled by the class implementing the java.io.Serializable interface. Classes that do not implement this interface will not have any of their state serialized or deserialized. Let’s understand the concept with an example.

Serialization of book object to stream:

objectOutputStream.writeObject(book1);

De-serialization of book object from the stream:

objectInputStream.readObject();

The writeObject() method is responsible for writing the state of the object for its particular class so that the corresponding readObject() method can restore it.

Consider the following Java class Book with the following instance variables.

 

Book Class

import java.io.Serializable;

public class Book implements Serializable {

    private static final long serialVersionUID = 1L;
    //Instance variables of the class
    private String title;
    private String publication;
    double price;

    // Constructor
    public Book(String title, String publication,double price) {
        this.title=title;
        this.publication=publication;
        this.price=price;
    }

    //tostring method
    public String toString() {
        return "Book Title:" + title + "\n"
        + "Publication:" + publication + "\n"
        + "Price: $" + price;
    }

}

 

Driver Class

Driver class is used to demonstrate the serialization and de-serialization process of the Book class.

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

 public class Driver {

 public static void main(String[] args) {
 Driver driver= new Driver();
  FileOutputStream fileOuputStream = null;
  ObjectOutputStream objectOutputStream = null;

  FileInputStream fileInputStream = null;
  ObjectInputStream objectInputStream = null;
  String filename = "bookObjects.data";
  // Instantiate objects
  Book book1=new Book("Java Made Easy","XYZ Publication",23.95);
  Book book2=new Book("Testing Made Easy","ABC Publication",95.0);

  try {
      fileOuputStream = new FileOutputStream(filename);
      objectOutputStream = new ObjectOutputStream(fileOuputStream);
      objectOutputStream.writeObject(book1);
      objectOutputStream.writeObject(book2);

       } catch (Exception ex) {
         ex.printStackTrace();
        } finally {
       if (fileOuputStream != null) {
          try {
           fileOuputStream.close();
            } catch (IOException e) {
              e.printStackTrace();
              }
                    }

       if (objectOutputStream != null) {
           try {
               objectOutputStream.close();
           } catch (IOException e) {
               e.printStackTrace();
           }
       }

  }
  try {
      fileInputStream = new FileInputStream(new File(filename));
      objectInputStream  = new ObjectInputStream(fileInputStream);

      // Read objects
      Book b1 = (Book) objectInputStream.readObject();
      Book b2 = (Book) objectInputStream.readObject();

      System.out.println("Books read from file:");
      System.out.println(b1.toString());
      System.out.println(b2.toString());


  } catch (Exception ex) {
      ex.printStackTrace();

  } finally {

      if (fileInputStream != null) {
          try {
              fileInputStream.close();
          } catch (IOException e) {
              e.printStackTrace();
          }
      }

      if (objectInputStream != null) {
          try {
              objectInputStream.close();
          } catch (IOException e) {
              e.printStackTrace();
          }
      }

  }
   }
 }

 

Program Output

Books read from file:
Book Title:Java Made Easy
Publication:XYZ Publication
Price: $23.95
Book Title:Testing Made Easy
Publication:ABC Publication
Price: $95.0