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Performance improvement techniques in Serialization


This topic illustrates the performance improvement techniques in Serialization with the following sections:

Overview of Serialization

Serialization is the process of writing complete state of java object into output stream, that stream can be file or byte array or stream associated with TCP/IP socket.

Deserialization is the process of reading back that serialized java object stream from input stream.

A java object is serializeable and deserializeable if that class follows the following rules

A) The java class must implement interface or interface or inherit that implementation from any one of it's super class implementation.

B) All instance variables of that class must implement Serializable interface or Externalizable interface or inherit from one of it's super class.

All primitive data types and some of standard java API classes are serializable. You need not explicitly implement Serializable or Externalizable interfaces for those classes. Serialization process ignores class (static) variables.

Externalizable interface allow to do your own custom implementation of serialization. In this section,  focus is only on Serializable interface.

We will talk initially about Serializable interface. This is a marker interface and does not have any methods. All major java technologies like RMI, EJB are based on serialization process to pass the objects through network. These technologies implicitly do all the serialization work for you. You need to simply implement the interface, but If you want to do your own serialization, that is reading from or writing to streams, ObjectInputStream and ObjectOutputStream  can be used.

These methods help to write into stream and read from stream

ObjectInputStream.readObject();                    // to read object

ObjectInputStream.writeObject(Object obj);  // to write object

Initially, We need to understand the default mechanism of serialization process in order to improve performance

The default mechanism:

When you write or read an object to a file or network or other stream using serialization process, It writes/reads the complete object state that means it writes the object, it's instance variables, and  super class instance variables except transient variables and class (static) variables. Look at this object hierarchy.



In this class hierarchy, when I write CorporateEmployee object into file and and read from that file, Initially Address is called, second HomeAddress is called, third Employee is called and finally CorporateEmployee is called. So Total object hierarchy will be written into file except transient and class (static) variables. Initially super class will be called and so on till end of heirarchy. You need to keep an eye on this mechanism and act up on that, otherwise you will end up with writing everything. The next section explains how to avoid unnecessary data in to streams and improve performance.

This section examples are tested on Windows millennium, 320mb RAM and JDK 1.3.

Note: This section assumes that reader has some basic knowledge of Java.

Optimization with 'transient'

Variables that have access modifier  'transient'  will not be read from or written into streams. It gives facility to avoid writing unnecessary data into streams. In other words, it boosts the performance by avoiding writing unnecessary data into streams.

Here is the code snippet to show the Serialization process with transient and non transient variation bench marks


package com.performance.serialization;

import java.util.Vector;


public class SerializationTest


             static long start,end;

             OutputStream out = null;

             InputStream in = null;

             OutputStream outBuffer = null;

             InputStream inBuffer = null;

             ObjectOutputStream objectOut = null;

             ObjectInputStream objectIn = null;

public Person getObject(){

              Person p = new Person("SID","austin");

              Vector v = new Vector();

              for(int i=0;i<7000;i++){




              return p;


public static void main(String[] args){

             SerializationTest st = new SerializationTest();

             start = System.currentTimeMillis();



             end = System.currentTimeMillis();

             System.out.println("Time taken for writing and reading :"+ (end-start) + "milli seconds");


public void readObject(){


                             in = new FileInputStream("c:/temp/test.txt");

                             inBuffer = new BufferedInputStream(in);

                             objectIn = new ObjectInputStream(inBuffer);


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


                             if(objectIn != null)

                             try{ objectIn.close();}catch(IOException e){e.printStackTrace();}



public void writeObject(){


                             out = new FileOutputStream("c:/temp/test.txt");

                             outBuffer = new BufferedOutputStream(out);

                             objectOut = new ObjectOutputStream(outBuffer);


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


                             if(objectOut != null)

                             try{ objectOut.close();}catch(IOException e){e.printStackTrace();}




 class Person implements


             private String name;

             private Vector data;

             private String address;

             public Person(String name,String address){

                    = name;

                             this.address = address;


             public String getAddress(){

                             return address;


             public Vector getData(){

                             return data;  


             public String getName(){

                             return name;


             public void setData(Vector data){

                    = data;




It writes the Person Object into file and reads from that file.

The output is

Time taken for writing and reading : 390 milli seconds

If I use 'transient' modifier for the Vector in the Person Object, then the output is

Time taken for writing and reading : 110 milli seconds

It almost increases the speed more than 3 times.

You need to use 'transient' keyword for unnecessary variables to increase performance.


Key Points

  1. Use 'transient' key word for unnecessary variables that need not be read from/written into streams.
  2. When you write RMI, EJB or any other technologies that uses built in Serialization to pass objects through network, use 'transient' key word for unnescessary variables.
  3. Class (static) variables ignores by Serialization process like 'transient' variables.

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