Question

My question is what is a good way to implement upgrading outdated objects?

For example say you have a class like this:

public class Foo() implements Serializable {
    int a;
    String b;
}

and then you serialize this object. Then later on you add more functionality to your class by say adding:

...
int c;
...

You still want to retain the information that is in the serialized object but I know that if you try to deserialize it there will be conflicts. So is there a way (maybe by checking serialVersionUID) to set a value for int c knowing that it won’t exist?

Thanks

Answer 1

You would need to add a private method:

    private void readObject(ObjectInputStream ois) {
      // compare serialVersionUID and determine which fields to expect
      // read the expected fields for that version
      // initialize the new fields.
    }

For more information, read the serialization specs