ObjectOutputStream is used to serialize Java objects—convert them into a byte stream so they can be written to files or sent over a network. It’s the counterpart of ObjectInputStream, which performs deserialization.
Commonly Used Constructors and Methods
The object being written must implement
Serializableinterface, orNotSerializableExceptionis thrown.
Simple Program – Serializing a Single Object
Mahesh wants to store an Employee object with an ID and name into a file using ObjectOutputStream so that LotusJavaPrince can later retrieve it.
import java.io.*;
class Employee implements Serializable {
int id;
String name;
Employee(int id, String name) {
this.id = id;
this.name = name;
}
}
public class SimpleObjectOutputStreamExample {
public static void main(String[] args) {
try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("employee.ser"))) {
Employee emp = new Employee(101, "LotusJavaPrince");
oos.writeObject(emp);
System.out.println("Employee object serialized.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
Output:
Employee object serialized.
//File employee.ser now contains the binary-serialized form of the object.Code language: JavaScript (javascript)Problem Statement:
LotusJavaPrince is building a bank record system where customer account objects need to be stored in a file for persistent storage. Each account contains:
- Account Number (int)
- Account Holder Name (String)
- Account Balance (double)
Mahesh helps write multiple such objects to a file using ObjectOutputStream.
import java.io.*;
class BankAccount implements Serializable {
int accNo;
String accHolder;
double balance;
BankAccount(int accNo, String accHolder, double balance) {
this.accNo = accNo;
this.accHolder = accHolder;
this.balance = balance;
}
}
public class BankAccountWriter {
public static void main(String[] args) {
try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("accounts.ser"))) {
// Create and serialize multiple accounts
BankAccount acc1 = new BankAccount(1001, "Mahesh", 7500.25);
BankAccount acc2 = new BankAccount(1002, "LotusJavaPrince", 15000.00);
BankAccount acc3 = new BankAccount(1003, "Paani", 9200.00);
oos.writeObject(acc1);
oos.writeObject(acc2);
oos.writeObject(acc3);
System.out.println("Multiple bank account objects serialized.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
Output:
Multiple bank account objects serialized.
// File accounts.ser contains all the serialized BankAccount objects.Code language: JavaScript (javascript)Behind the Scenes
- When
writeObject()is called, Java performs deep serialization of the object. - Fields that are not serializable must be marked
transient. - Static fields are not serialized as they belong to the class, not the instance.
ObjectOutputStream is ideal for serializing full Java objects to a binary stream.
- It is commonly used with
FileOutputStream,Socket.getOutputStream(), orByteArrayOutputStream. - To deserialize the object, use
ObjectInputStream.