How to serialize a non-serializable in Java?

Question

How can I serialize an object that does not implement Serializable? I cannot mark it Serializable because the class is from a 3rd party library.

Answer 1

You can't serialise a class that doesn't implement Serializable, but you can wrap it in a class that does. To do this, you should implement readObject and writeObject on your wrapper class so you can serialise its objects in a custom way.

• First, make your non-serialisable field transient.
• In writeObject, first call defaultWriteObject on the stream to store all the non-transient fields, then call other methods to serialise the individual properties of your non-serialisable object.
• In readObject, first call defaultReadObject on the stream to read back all the non-transient fields, then call other methods (corresponding to the ones you added to writeObject) to deserialise your non-serialisable object.

I hope this makes sense. :-)

Answer 2

Wrap the non-serializable class in a class of your own that implements Serializable. In your class's writeObject method, do whatever's necessary to serialize sufficient information on the non-serializable object so that your class's readObject method can reconstruct it.

Alternatively, contact the developer of the non-serializable class and tell him to fix it. :-)

Answer 3

You can use Kryo. It works on non serialized classes but classes needs registered aforehand.

Answer 4

If your class already implements the Serializable interface (required for serializing), all you must do is to declare the field you don't want to serialize with transient:

    public transient String description;

Answer 5

If the class is not final, you can make your own class that extends it and implements Serializable. There are lots of other ways to serialize besides Java's built-in mechanism though.