Custom Serialization: writeObject and readObject

By implementing the Serializable interface we can use Java default serializable.

However we can customize the serialization process by implementing writeObject() and/or readObject() methods.

These methods are not overridden Because we are actually not overriding anything: The JVM checks and calls these methods by the means of reflection.

import java.io.IOException;

import java.io.InvalidObjectException;

import java.io.ObjectInputValidation;

import java.io.ObjectStreamException;

import java.io.Serializable;

public class Pojo implements Serializable, ObjectInputValidation {

       public Pojo(String msg) {

              this.msg = msg;

       }

       private String msg;

       private void writeObject(java.io.ObjectOutputStream out)

                     throws IOException {

              System.out.println("writeObject");

              out.defaultWriteObject();

       }

       private Object writeReplace() throws ObjectStreamException {

              System.out.println("writeReplace");

              return this;

       }

       private void readObject(java.io.ObjectInputStream in)

                     throws IOException, ClassNotFoundException {

              System.out.println("readObject");

              in.registerValidation(this, 0);

              in.defaultReadObject();

       }

       @Override

       public void validateObject() throws InvalidObjectException {

              System.out.println("validateObject");

       }

       private Object readResolve() throws ObjectStreamException {

              System.out.println("readResolve");

              return this;

       }

       public String getMsg() {

              return msg;

       }

}

import java.io.ByteArrayInputStream;

import java.io.ByteArrayOutputStream;

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

import java.io.ObjectOutputStream;

public class CustomSerialiazation {

       public static void main(String[] args) throws Exception {

              Pojo pojo = new Pojo("Hello world");

              byte[] bytes = serialize(pojo); // Serialization       

              Pojo p = (Pojo) deserialize(bytes); // De-serialization

              System.out.println(p.getMsg());

       }

       private static byte[] serialize(Object o) throws IOException {

              ByteArrayOutputStream baos = new ByteArrayOutputStream();

              ObjectOutputStream oos = new ObjectOutputStream(baos);

              oos.writeObject(o);

              oos.flush();

              oos.close();

              return baos.toByteArray();

       }

       private static Object deserialize(byte[] bytes)

                     throws ClassNotFoundException, IOException {

             ByteArrayInputStream bais = new ByteArrayInputStream(bytes);

              ObjectInputStream ois = new ObjectInputStream(bais);

              Object o = ois.readObject();

              ois.close();

              return o;

       }

}