In java, is it possible to add the Serializable interface to class that doesn't have it at runtime?

Question

There is a class I want to serialize, and it implements Serializable, but one of the objects it contains does not implement Serializable.

Is there a way to modify the class at runtime to make it implement the Serializable interface so I can serialize it? I can't change it at compile time because its a third party library.

Maybe I would have to use some sort of bytecode writer or something?

EDIT: Both the containing class and contained class are in the 3rd party library so I don't think i can mark something as transient. The containing class is marked as serializable, but it contains an object that is not.

I'm fine with writing a custom serialization method for the class, not sure how I would do this though, would I have to use reflection to get the values of the private variables?

Answer 1

Reading the javadoc for Serializable, I see:

Classes that require special handling during the serialization and deserialization process must implement special methods with these exact signatures:

private void writeObject(java.io.ObjectOutputStream out)
     throws IOException
 private void readObject(java.io.ObjectInputStream in)
     throws IOException, ClassNotFoundException;
 private void readObjectNoData() 
     throws ObjectStreamException;

which you could use to manually serialize the uncooperative fields. You could look into using ASM, but it seems hard to believe that it is a maintainable solution.

Answer 2

Fields can be skipped using the transient modifier. Additional data can be added to the stream by providing readObject and writeObject methods. Classes can be subclassed to make them serialisable (though you will need to manage the superclass data), or use a serial proxy (see Effective Java).