Lesson 45: Object Serialization and Deserialization

Serialization is the process of converting an object's state into a sequence of bytes (a stream). This stream can then be saved to a file or transmitted across a network.

Deserialization is the reverse process: reconstructing the object from the stream of bytes.

1. Making a Class Serializable

For an object to be serializable, its class must implement the marker interface java.io.Serializable.

java import java.io.Serializable;

public class Employee implements Serializable { // Fields must also be serializable, or marked 'transient' private String name; private int id;

// transient fields are ignored during serialization
private transient String password; 

// Best practice: add a unique ID for version control
private static final long serialVersionUID = 1L;

}

2. Serialization (Writing the Object)

We use ObjectOutputStream, which must wrap a byte stream (like FileOutputStream).

java // Output Stream try (FileOutputStream fileOut = new FileOutputStream("employee.ser"); ObjectOutputStream objOut = new ObjectOutputStream(fileOut)) {

Employee emp = new Employee("John", 101);
objOut.writeObject(emp); // Write the entire object to the stream
System.out.println("Employee object serialized.");

} catch (IOException i) { i.printStackTrace(); }

3. Deserialization (Reading the Object)

We use ObjectInputStream and must cast the read Object back to the specific class type.

java // Input Stream try (FileInputStream fileIn = new FileInputStream("employee.ser"); ObjectInputStream objIn = new ObjectInputStream(fileIn)) {

Employee e = (Employee) objIn.readObject(); // Read and cast
System.out.println("Employee deserialized: " + e.getName());

} catch (IOException | ClassNotFoundException e) { e.printStackTrace(); }