Java.Serialization.What are the ways to control the values ​​of the deserialized object

🔧 1. Use a Custom readObject() Method

This is the standard way to hook into deserialization:

private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
    in.defaultReadObject(); // Restore default values

    // 💡 Customize here
    if (age < 0) age = 0; // Validation
    if (nickname == null) nickname = "Anonymous";
}

🔍 What this gives you:

• Access to the object’s fields right after they’re deserialized
• The ability to change, correct, or fill in missing/transient data

🔐 2. Use readResolve() to Replace the Object

This is great for:

• Singletons
• Immutable instances
• Object deduplication

private Object readResolve() throws ObjectStreamException {
    // Replace the deserialized object with a canonical one
    return MyObjectRegistry.getInstanceById(this.id);
}

➕ Bonus:

• You can return a completely different object than the one Java just built

🧪 3. Use transient + Reinitialization Logic

Fields marked as transient are skipped during serialization. You can:

• Add default values in readObject()
• Recalculate them using other deserialized fields

transient String cache;

private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
    in.defaultReadObject();
    this.cache = this.name.toUpperCase(); // Restore derived field
}

🛡 4. Validate Object with ObjectInputValidation (less common)

This is a special hook for post-processing:

in.registerValidation(obj -> {
    if (obj.age < 0) throw new InvalidObjectException("Invalid age!");
}, 0);

✅ Used for deep validation or dependency-based checks.

⚠️ 5. Constructor Does Not Run During Deserialization!

Remember:

• Java bypasses constructors during deserialization using ReflectionFactory
• So if you rely on constructor logic (e.g., init defaults), you need to repeat it in readObject()

🧵 TL;DR — How to Control Values on Deserialization

Method	What It Controls	When to Use
readObject()	Modify, validate, reinitialize fields	Most flexible and common
readResolve()	Replace the whole object	For Singletons, canonical forms
transient + reinit	Skip field + restore manually	Derived/cached/volatile data
ObjectInputValidation	Validate after full object graph is read	Advanced validation logic