Serialization in java

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Serialization in java

Posted by Unknown Friday 22 November 2013 0 comments

I will explain you what is java serialization, then provide you with a sample for serialization. Finally most importantly, lets explore what is inside a serialized object and what it means. That is internals of java serialization and how does it works. If you want to have your own implementation of java serialization, this article will provide you good knowledge on Serialization concept.

Java Serialization?

Primary purpose of java serialization is to write an object into a stream, so that it can be transported through a network and that object can be rebuilt again. When there are two different parties involved, you need a protocol to rebuild the exact same object again. Java serialization API just provides you that. Other ways you can leverage the feature of serialization is, you can use it to perform a deep copy.
Why I used ‘primary purpose’ in the above definition is, sometimes people use java serialization as a replacement for database. Just a placeholder where you can persist an object across sessions. This is not the primary purpose of java serialization. Sometimes, when I interview candidates for Java I hear them saying java serialization is used for storing (to preserve the state) an object and retrieving it. They use it synonymously with database. This is a wrong perception for serialization.

How do you serialize?

When you want to serialize an object, that respective class should implement the marker interface serializable. It just informs the compiler that this java class can be serialized. You can tag properties that should not be serialized as transient. You open a stream and write the object into it. Java API takes care of the serialization protocol and persists the java object in a file in conformance with the protocol. De-serialization is the process of getting the object back from the file to its original form.
Here protocol means, understanding between serializing person and de-serializing person. What will be the contents of file containing the serialized object? This serves as a guideline to de-serialize.

package com.serial.sample;

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 java.io.Serializable;

class SerializationEx implements Serializable {

  private byte serializableProp = 10;

  public byte getSerializableProp() {

    return serializableProp;

  }

}

public class SerializationSample {

  public static void main(String args[]) throws IOException,

      FileNotFoundException, ClassNotFoundException {

    SerializationEx serialB = new SerializationEx();

    serialize("serial.out", serialB);

    SerializationEx sb = (SerializationEx) deSerialize("serial.out");

    System.out.println(sb.getSerializableProp());

  }

  public static void serialize(String outFile, Object serializableObject)

      throws IOException {

    FileOutputStream fos = new FileOutputStream(outFile);

    ObjectOutputStream oos = new ObjectOutputStream(fos);

    oos.writeObject(serializableObject);

  }

  public static Object deSerialize(String serilizedObject)

      throws FileNotFoundException, IOException, ClassNotFoundException {

    FileInputStream fis = new FileInputStream(serilizedObject);

    ObjectInputStream ois = new ObjectInputStream(fis);

    return ois.readObject();

  }

}

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