CUSTOMIZED SERIALIZATION IN JAVA

Transient keyword – Transient keyword is applicable only for variables. At the time of serialization if we don’t want to save the original value of a particular variable to meet the security constraints, such type of variables should be declared with transient keyword. At the time of serialization jvm ignores the original value of transient variable and saves default values. Hence transient means not to serialize.

Transient v/s Static – static variable aren’t part of object state. Hence they don’t participate in serialization. Declaring static variable as transient has no impact. Example – transient static int i=10; Output - i=10.

But transient int i=10; Output – i=0;

Transient v/s final – Final variables will participate in serialization directly by their values. Hence declaring the final variable as transient has no impact (because every final variable is replaced by value at the time of compilation only). Example – transient final int j=10; Output – j=10;

Customized Serialization – During default Serialization there may be a chance of loss of information due to transient keyword.

Example – To implement loss of object data into 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;

class Example implements java.io.Serializable{

          private String uname;

          private transient String upwd;

          public String getUname() {

                   return uname;

          }

          public void setUname(String uname) {

                   this.uname = uname;

          }

          public String getUpwd() {

                   return upwd;

          }

          public void setUpwd(String upwd) {

                   this.upwd = upwd;

          }

}

public class TransientImple {

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

                   Example e1 = new Example();

                   e1.setUname("rakesh");

                   e1.setUpwd("pw1234");

                   ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("xyz.txt"));

                   oos.writeObject(e1);

                   ObjectInputStream ois = new ObjectInputStream(new FileInputStream("xyz.txt"));

                   Example e2 = (Example)ois.readObject();

                   System.out.println(e2.getUname());

                   System.out.println(e2.getUpwd());

          }

}

Output –

rakesh

null

Explanation – In the above program before performing serialization Example object can provide proper username and password but after Deserialization Example object can provide only username but not password. This is due to transient keyword. Hence during default serialization there may be a chance of loss of information due to transient keyword. We can recover this loss of information by using atomized serialization. We can implement customized serialization by using the following two methods –

1. private void writeObject(ObjectOutputStream os) throws Exception – This method will be executed automatically at the time of serialization, if we want to perform any extra work we have to define that inside this method only.

2. private void readObject(ObjectInputStream is) throws Exception – This method will be executed automatically at the time of Deserialization. Hence, at the time of Deserialization we want to perform any extra work. We have to define that inside method only.

Example – To implement loosing the value of object and recovering that object and to store in a 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; 

class Example1 implements java.io.Serializable{

          private String uname;

          private transient String upwd;

          public String getUname() {

                   return uname;

          }

          public void setUname(String uname) {

                   this.uname = uname;

          }

          public String getUpwd() {

                   return upwd;

          }

          public void setUpwd(String upwd) {

                   this.upwd = upwd;

          }

          private void writeObject(ObjectOutputStream os)throws Exception

          {

                   os.defaultWriteObject();

                   String epass="e123"+upwd;

                   os.writeObject(epass);

          }

          private void readObject(ObjectInputStream is)throws Exception

          {

                   is.defaultReadObject();

                   String epass=(String)is.readObject();

                   upwd=epass.substring(4);

          }

}

public class Trans2 {

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

                   Example1 e1 = new Example1();

                   e1.setUname("rakesh");

                   e1.setUpwd("pw1234");

                   ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("lmn.txt"));

                   oos.writeObject(e1);

                   ObjectInputStream ois = new ObjectInputStream(new FileInputStream("lmn.txt"));

                   Example1 e2 = (Example1)ois.readObject();

                   System.out.println(e2.getUname());

                   System.out.println(e2.getUpwd());

          }

}

Output –

rakesh

pw1234

Explanation – In the above example Example1 class the writeObject() and readObject() methods will be executed automatically by the jvm. Hence these are callback methods.