How to write a object in file (Serialization) (Java)

How to write a object in file (Serialization) (Java):

  -> Sending an object to a stream, to some file or somewhere on network.

  -> Object know how to read/write themselves to streams.

Serialization is also called as flattening, Streaming, Dehydrate (rehydrate = read), Archiving.

Serializable Interface:

              By implementing this interface a class declares that is willing to  be read/written by automatic serializable machinery. import java.io.*; for using serialization.

 Automatic Writing:

     System knows how to recursively write out the state of an object to stream.

     Recursively follows references and writes out those objects too!

 Automatic Reading: 

     System knows how to read the data from Stream and re-create object in memory

     Downcasting is required

Code

 

Creating an Employee class which contains id, name , default and parameterized constructor and one method print(). To serialize an object class have to implement Serializable interface.

import java.io.*;

public class Employee implements Serializable {

    private int id;

             

    private String name;

       

  // Default Constructor

     public Employee() {

             

              this.id = 0;

              this.name = "Anonymous";

    }

      

  // Parametrized Constructor

    public Employee(int i , String n) {

             

              this.id = i;

              this.name = n;

    }

  

    public void print() {

             

              System.out.println("Id Is : " + this.id +

                                  "\n Name Is : " + this.name );

   }

}

DRIVER CLASS FOR EXECUTING PROGRAM:

public class Driver {

  public static void main(String[] args) {

      

      try {

              

SERIALIZING A SINGLE OBJECT:

 

Creating an Employee class object:

         

        Employee emp = new Employee(1, "osama");

For writing aan object to file create FileOutputStream object and pass the path of file as argument:

        

        FileOutputStream fos = new FileOutputStream("D:\\a.ser");

        

Now, create ObjectOutputStream object and in its constructor pass FileOutputStream object as argument:

         

        ObjectOutputStream oos = new ObjectOutputStream(fos);

  

.writeObject() is the method ObjectOutputStream class which takes one argument the object that is to be serialized, here that object is of Employee class:

       oos.writeObject(emp);

             

 

       } catch (Exception e) {

             e.printStackTrace();

       }

      } 
}      

SERIALIZING THE WHOLE ARRAYLIST OF EMPLOYEE OBJECTS:

import java.io.*;

import java.util.*;

public class Driver {

  public static void main(String[] args) {

      

       try {

             

           

Creating ArrayList which can hold Employee class objects:

        

          ArrayList<Employee> listEmployee = new ArrayList<Employee>();

Adding Employee objects in ArrayList:

          listEmployee.add(new Employee(1, "osama"));

          listEmployee.add(new Employee(2, "saad"));

          listEmployee.add(new Employee(3, "bilal"));

          listEmployee.add(new Employee(4, "shizzi"));

          listEmployee.add(new Employee(5, "hamza"));

For writing an object to file create FileOutputStream object and pass the path of file as argument:

          FileOutputStream fos = new FileOutputStream("D:\\a.ser");

Now, create ObjectOutputStream object and in its constructor pass FileOutputStream object as argument:

 

          ObjectOutputStream oos = new ObjectOutputStream(fos);

Here, writing / serializing a ArrayList object to file, in this way you can do it or the other way is, you can run loop and add the Employee objects in file one by one:

          oos.writeObject(listEmployee);

          } catch (Exception e) {

               e.printStackTrace();

         }

           

    }                   

}

 
WRITING OBJECTS IN FILE ONE BY ONE:

    for (int i = 0 ; i < listEmployee.size() ; i++) {

              

Getting each object from listEmployee and cast to Employee:

           Employee emp = (Employee)listEmployee.get(i);

And write the object in file:

           oos.writeObject(emp);

    }