16.4. Deserialization

Deserialization is the process of converting a byte stream back into a copy of the original object.

Deserialization is essentially the reverse of serialization. When an object is serialized, it is converted into a byte stream to be saved or transmitted. Deserialization takes that byte stream and reconstructs the original object. This process allows for the retrieval of the object's state, meaning the values of its fields are restored to what they were at the time of serialization.

You can think of deserialization like reassembling a jigsaw puzzle. When you serialize an object, it's like taking a picture of a completed puzzle – you can share or store the picture, but the pieces are scattered. Deserialization is akin to putting the puzzle back together using the pieces from the picture, bringing back the whole image.

To deserialize an object, you can read it from a file using a FileInputStream and ObjectInputStream to retrieve it.

The code provided demonstrates how to read a serialized object from a file. First, you create a FileInputStream to open the file that contains the serialized object. Then, an ObjectInputStream is created, which allows you to read Java objects from the byte stream. When you call readObject(), it converts the byte stream back into the original object type, which in this case is Student. Closing the streams is essential afterward to free up system resources.

Imagine you stored a secret recipe in a vault (the file). To retrieve the recipe, you need to open the vault and pull out the recipe page. The FileInputStream is like the key to the vault, while the ObjectInputStream is the process of reading the recipe once you've accessed it.

Here’s a simple Java code example for deserialization:

import java.io.*;
public class DeserializeDemo {
    public static void main(String[] args) throws Exception {
        FileInputStream fis = new FileInputStream("student.ser");
        ObjectInputStream ois = new ObjectInputStream(fis);
        Student s = (Student) ois.readObject();
        ois.close();
        fis.close();
        System.out.println("Deserialized Student: " + s.getName());
    }
}

This code example shows how to deserialize a Student object from a file named student.ser. After setting up the FileInputStream and ObjectInputStream, it reads the serialized object using readObject() and casts it back to the Student type. Finally, it prints the name of the deserialized student. This process emphasizes how the original details of the object can be restored from the byte stream.

Think of this process like retrieving a saved game. When you read the game file, the computer reconstructs the exact state of your character, including health, items, and level. Just like the game remembers your progress, deserialization recreates the original object with all its information intact.

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