Serialization & De-serialization in Java

Serialization & De-serialization in Java
When you create a class, you may create an object for that particular class and once
we execute/terminate the program, the object is destroyed by itself (Garbage Collector
thread).
What happens if you want to call that class without re-creating the object. In those
cases what you do is that, we use the serialization concept by convert data into byte
stream.
Object Serialization is a process used to convert state of an object into byte stream
which can be persisted into disk/file or sent over network to any other running Java
virtual machine; and the reverse process of creating object from byte stream is called
deserialization in Java.The byte stream created is platform independent. So, the
object serialized on one platform can be deserialized on a different platform.
How to make a java class Serializable ?
Serializability can be enabled of your java class by implementing the
java.io.Serializable interface. It is a marker interface that means it contains no
methods or fields and only serves to identify the semantics of being serializable.
What if we are trying to serialize a non-serializable object?
We will get RuntimeException saying :
Exception in thread "main" java.io.NotSerializableException:
java.io.ObjectOutputStream.
What is serialVersionUID ?
SerialVersionUID is an ID which is stamped on object when it get serialized usually
hashcode of object. We can find serialVersionUID for the object by serialver tool of
java.

Syntax : serialver classname
SerialVersionUID is used for version control of object. Consequence of not specifying
serialVersionUID is that when you add or modify any field in class then already
serialized class will not be able to recover because serialVersionUID generated for
new class and for old serialized object will be different. Java serialization process
relies on correct serialVersionUID for recovering state of serialized object and throws
java.io.InvalidClassException in case of serialVersionUID mismatch.
transient keyword :
transient modifier/keyword applicable only for variables but not for methods and
classes.
At the time of serialization if we don't want to serialize the value of a particular
variable to meet security constraints then we should declare that variable as transient.
While performing serialization JVM ignores original value of transient variable and
save default value to the file.
Hence transient means not to serialize.
transient v/s static :
Static variable is not part of object state and hence it won't participate in serialization.
Due to this declaring static variable as transient, there is no use.
final v/s transient :
final variables will be participated in serialization directly by the value.Hence
declaring a final variable as transient , there is no impact.
Now, let us consider a program which shows Serialization & De-serialization in java :
This POJO class Employee implements Serializable interface :
package com.java.serialization;
import java.io.Serializable;
public class Employee implements Serializable {
private static final long serialVersionUID = 1L;

private String serializeValueName;
private transient int nonSerializeValueSalary;
public String getSerializeValueName() {
return serializeValueName;
}
public void setSerializeValueName(String serializeValueName) {
this.serializeValueName = serializeValueName;
}
public int getNonSerializeValueSalary() {
return nonSerializeValueSalary;
}
public void setNonSerializeValueSalary(int
nonSerializeValueSalary) {
this.nonSerializeValueSalary =
nonSerializeValueSalary;
}
@Override
public String toString() {
return "Employee [serializeValueName=" +
serializeValueName + "]";
}
}
The following SerializingObject program instantiates an Employee object and
serializes it to a file.

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
public class SerializingObject {
public static void main(String[] args) {
Employee employeeOutput = null;
FileOutputStream fos = null;
ObjectOutputStream oos = null;
employeeOutput = new Employee();
employeeOutput.setSerializeValueName("Aman");
employeeOutput.setNonSerializeValueSalary(50000);
try {
fos = new FileOutputStream("Employee.ser");
oos = new ObjectOutputStream(fos);
oos.writeObject(employeeOutput);
System.out.println("Serialized data is saved in
Employee.ser file");
oos.close();
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
OUTPUT :
Serialized data is saved in Employee.ser file.
The following DeSerializingObject program deserializes the Employee object created
in the SerializingObject program.
import java.io.FileInputStream;

import java.io.IOException;
import java.io.ObjectInputStream;
public class DeSerializingObject {
public static void main(String[] args) {
Employee employeeInput = null;
FileInputStream fis = null;
ObjectInputStream ois = null;
try {
fis = new FileInputStream("Employee.ser");
ois = new ObjectInputStream(fis);
employeeInput = (Employee)ois.readObject();
System.out.println("Serialized data is restored
from Employee.ser file");
ois.close();
fis.close();
} catch (IOException | ClassNotFoundException e) {
e.printStackTrace();
}
System.out.println("Name of employee is : " +
employeeInput.getSerializeValueName());
System.out.println("Salary of employee is : " +
employeeInput.getNonSerializeValueSalary());
}
}
OUTPUT :
Serialized data is restored from Employee.ser file
Name of employee is : Aman
Salary of employee is : 0

Serialization & De-serialization in Java

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Serialization & De-serialization in Java