Serialization and Deserialization in java.

Serialization is the process of converting the state of an object into byte stream. De-serialization allow you to restore the serialized state into another instance of the same type. As you know, only the state of an object can serialized. Behavior is run-time phenomenon and it can’t be converted to a stream. Classes java.io.ObjectOutputStream and java.io.ObjectInputStream are provide necessary APIs to serialize and deserialize an object.

Serialization

In general, there are three steps involved in serializing a java object.

Marking the class as Serializable
Create an instance of ObjectOutputStream
Use writeObject method of ObjectOutputStream to write the object into stream

Marking the class as Serializable

It just informs the compiler that this java class may be serialized. java.io.Serializable is a marker interface.

class Laptop implements java.io.Serializable{}

1	class Laptop implements java.io.Serializable{}

Create an instance of java.io.ObjectOutputStream

ObjectOutputStream objectStream = new ObjectOutputStream(new FileOutputStream(
new File(<<file_name>>)));

1 2	ObjectOutputStream objectStream = new ObjectOutputStream(new FileOutputStream( new File(<<file_name>>)));

Write object to underlying output stream

ObjectOutputStream objectStream = new ObjectOutputStream(new FileOutputStream(
new File(<<file_name>>)));
objectStream.writeObject(object);

ObjectOutputStream objectStream = new ObjectOutputStream(new FileOutputStream(

new File(<<file_name>>)));

objectStream.writeObject(object);

Important API to serialize an object

Class Name : java.io.ObjectOutputStream
Method Name : public final void writeObject(Object x) throws IOException

1 2	Class Name : java.io.ObjectOutputStream Method Name : public final void writeObject(Object x) throws IOException

Deserialization

Deserialization is process of restoring the serialized state of an object. In general, there are three steps involved in deserialization.

Load the serialized state as stream
Create an object of the java.io.ObjectInputStream with stream loaded in step one
Read the object and cast to correct type

Load the serialized state as stream

final FileInputStream inputStream = new FileInputStream(new File(<<file_name>>));

1	final FileInputStream inputStream = new FileInputStream(new File(<<file_name>>));

Create an object of the ObjectInputStream with stream loaded in step one

final ObjectInputStream objectStream = new ObjectInputStream(inputStream);

1	final ObjectInputStream objectStream = new ObjectInputStream(inputStream);

Read the object and cast to correct type

final ObjectInputStream objectStream = new ObjectInputStream(inputStream);
final Laptop laptop = (Laptop)objectStream.readObject();

1 2	final ObjectInputStream objectStream = new ObjectInputStream(inputStream); final Laptop laptop = (Laptop)objectStream.readObject();

Important API to Deserialize an object

Class Name : java.io.ObjectInputStream
Method Name : public final Object readObject() throws IOException

1 2	Class Name : java.io.ObjectInputStream Method Name : public final Object readObject() throws IOException

Complete Example Code

package com.ourownjava.corejava.io;
import static org.junit.Assert.assertEquals;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import org.junit.Before;
import org.junit.Test;
/**
*
* @author ourownjava.com
*
* Example program for java serialization and de-serialization
*
*/
public class SerializationBehavior {
private File file;
private Laptop laptop;
@Before
public void setUp(){
file = new File("/home/thosan/java/testfiles/laptop");
laptop = new Laptop();
laptop.setMake("Dell");
laptop.setPrice(1000.10);
laptop.setPrimaryMemorySize(4056);
}
@Test
public void shouldSerializeLaptopObject() throws FileNotFoundException, IOException{
file.delete();
file.createNewFile();
assertEquals(0, file.length());
final ObjectOutputStream objectInputStream = new ObjectOutputStream(new FileOutputStream(file));
objectInputStream.writeObject(laptop);
assertEquals(129, file.length());
objectInputStream.close();
}
@Test
public void shouldDeserializeLaptopObject() throws FileNotFoundException, IOException, ClassNotFoundException{
final ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(file));
Laptop laptop = (Laptop) objectInputStream.readObject();
assertEquals("Dell", laptop.getMake());
assertEquals(Double.valueOf(1000.10), Double.valueOf(laptop.getPrice()));
assertEquals(4056, laptop.getPrimaryMemorySize());
objectInputStream.close();
}
}

package com.ourownjava.corejava.io;

import static org.junit.Assert.assertEquals;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

import org.junit.Before;

import org.junit.Test;

/**

* @author ourownjava.com

* Example program for java serialization and de-serialization

public class SerializationBehavior {

private File file;

private Laptop laptop;

@Before

public void setUp(){

file = new File("/home/thosan/java/testfiles/laptop");

laptop = new Laptop();

laptop.setMake("Dell");

laptop.setPrice(1000.10);

laptop.setPrimaryMemorySize(4056);

}

@Test

public void shouldSerializeLaptopObject() throws FileNotFoundException, IOException{

file.delete();

file.createNewFile();

assertEquals(0, file.length());

final ObjectOutputStream objectInputStream = new ObjectOutputStream(new FileOutputStream(file));

objectInputStream.writeObject(laptop);

assertEquals(129, file.length());

objectInputStream.close();

}

@Test

public void shouldDeserializeLaptopObject() throws FileNotFoundException, IOException, ClassNotFoundException{

final ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(file));

Laptop laptop = (Laptop) objectInputStream.readObject();

assertEquals("Dell", laptop.getMake());

assertEquals(Double.valueOf(1000.10), Double.valueOf(laptop.getPrice()));

assertEquals(4056, laptop.getPrimaryMemorySize());

objectInputStream.close();

}

package com.ourownjava.corejava.io;
import java.io.Serializable;
/**
*
* @author ourownjava.com
*
*/
public class Laptop implements Serializable{
private static final long serialVersionUID = -1;
private String make;
private int primaryMemorySize;
private double price;
public String getMake() {
return make;
}
public void setMake(String make) {
this.make = make;
}
public int getPrimaryMemorySize() {
return primaryMemorySize;
}
public void setPrimaryMemorySize(int primaryMemorySize) {
this.primaryMemorySize = primaryMemorySize;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
}

package com.ourownjava.corejava.io;

import java.io.Serializable;

/**

* @author ourownjava.com

public class Laptop implements Serializable{

private static final long serialVersionUID = -1;

private String make;

private int primaryMemorySize;

private double price;

public String getMake() {

return make;

}

public void setMake(String make) {

this.make = make;

}

public int getPrimaryMemorySize() {

return primaryMemorySize;

}

public void setPrimaryMemorySize(int primaryMemorySize) {

this.primaryMemorySize = primaryMemorySize;

}

public double getPrice() {

return price;

}

public void setPrice(double price) {

this.price = price;

}