How can I have more flexible serialization and deserialization in Java?

Question

If I serialize an object in Java, and then later add an extra field to the java class, I can't deserialize the object into the modified class.

Is there a serialization library or some way that I can have deserialization be less strict, like if there is an extra field added to the class then it just fills that with null upon deserialization of the old version of the class?

Answer 1

You need to keep a serialVersionUID on your class. Check out the section "Version Control" in this article by Sun.

Answer 2

You've got lots of potential options.

You could use a graph serialisation library to define and manage your format e.g. Google's protocol buffers or Kryo. I believe both of these have built-in support for versioning.

You can write your own custom serialisation code and handle the versions explicitly - e.g. serializing to a flexible format like XML. When reading the XML you can configure it to use default values if a particular field isn't specified.

Or you could design your class in a "flexible" way, e.g. have all the fields stored in a HashMap and indexed by Strings. Depending on what you are trying to do, this may be a convenient option.