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How to Serialize an Object in Java ?.

Updated on September 17, 2014

Introduction

In this tutorial, you will learn how Serialization process work in Java. Serialization is one of the most important aspect in dealing with Java Web Applications. So, what do we mean by Serialization in Java ?.

Serialization is a process of saving state of an Java object to a sequence of bytes. These sequence of bytes can be sent over a network, stored in a database or stored in a file. Writing an Java object to a file, database or sent over a network is called as Serialization. The process of reading back a Java object from file, database or network is called as De-serialization.

Conditions for Serialization in Java

  1. The class instance which we want to serialize must implement an interface by name Serializable. This interface is in the Java package java.io. It is a marker interface and does not contain any method to implement. It only signifies that whichever class implements it can be serialized to a file, database, memory or network.
  2. All of the fields or properties in a class must implement serializable interface. If not, that field has to be made transient.

Serialization process in Java

De-Serialization process in Java

What is Serialization in Java ?.

Reading and Writing a Java object to a file

Employee object to serialize

import java.io.Serializable;

// Create a class Employee, whose objects we want to 
// serialize. 
// Employee class must implement Serializable interface.
// It is a marker interface with no methods. It only provides 
// information that Employee objects can be serialized.
public class Employee implements Serializable {

	// Create two properties say, name and age.
	// These properties will be saved to a file.
	private String name;
	private int age;
	
	// Create getters and setters of name and age.
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}	
}

Java code - Serialization Demo

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;

// Create a Java class to demonstrate process of Serialization
public class SerializationDemo {
	
	// Create a main method in which steps for serializing an object
	// will be followed.
	public static void main(String[] args) {
 
		// Create an instance of Employee class which we want to serialize.		
		Employee employee = new Employee();
		
		// Set name and age of Employee instance as "Dinesh Varyani" and 
		// 27. These values will be saved to a file to demonstrate serialization process.
		employee.setName("Dinesh Varyani");
		employee.setAge(27);
				
		try {
			
			// In order to serialize Employee instance created above to a file. We have
			// to provide location to a file and attach a file output stream which will help in 
			// serializing object to the file. The file along with location is used as "/employee.ser"
			FileOutputStream fos = new FileOutputStream("/employee.ser");
			
			// In order to serialize an object we have to create an instance of Object Output
			// Stream. This Object Output Stream will be taking in help of File Output Stream 
			// instance to serialize a Java object.
			ObjectOutputStream oos = new ObjectOutputStream(fos); 
		    
			// Object Output Stream has a method by name writeObject. This method takes in 
			// a object of Employee which we want to serialize. writeObject method takes in help
			// File Output Stream and saves values of Employee such as name and age to 
			// employee.ser file.
			oos.writeObject(employee);
			
			// close Object Output Stream.
		    oos.close();
		    
		    // close File Output Stream.
		    fos.close();
		} catch (IOException e) {			
			e.printStackTrace();
		}		
	}
}

Java code - Deserialization Demo

import java.io.FileInputStream;
import java.io.IOException;
import java.io.ObjectInputStream;

// Create a Java class to demonstrate process of DeSerialization.
public class DeserializationDemo {

	// Create a main method in which steps for de-serializing an object
	// will be followed.
	public static void main(String[] args) {

		try {

			// In order to de-serialize an Employee instance serialized to a file in above class. We have
			// to provide location to a file and attach a file input stream which will help in 
			// de-serializing object from the file. The file along with location is used as "/employee.ser"
			FileInputStream fis = new FileInputStream("/employee.ser");

			// In order to de-serialize an object we have to create an instance of Object Input
			// Stream. This Object Input Stream will be taking in help of File Input Stream 
			// instance to de-serialize a Java object.
			ObjectInputStream ois = new ObjectInputStream(fis);

			// Object Input Stream has a method by name readObject. This method reads back a 
			// serialized object from file. readObject method takes in help File Input Stream and 
			// reads values of Employee such as name and age from employee.ser file.
			// It returns back an instance of Object class which we have to typecast back to 
			// Employee class.
			Employee employee = (Employee) ois.readObject();
			
			// close Object Input Stream.			
			ois.close();
			
			// close File Input Stream
			fis.close();
			
			// Print the information of the de-serialized object on the Java console.
			System.out.println("Employee Name: " + employee.getName());
			System.out.println("Employee Age: " + employee.getAge());
			
		} catch(Exception e) {
			e.printStackTrace();
		}
	}
}


Output of the Deserialization Demo class

On running SerializationDemo class, code saves properties of Employee instance such as

  • name - Dinesh Varyani
  • age - 27

to employee.ser file. On running DeserializationDemo class it reads back the properties values from employee.ser file and prints output on the Java console as shown in above image.

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