Write object with transient attributes to stream (Java)

Question

I want to write an object into a stream (or byte array) with its transient attributes to be able to reconstruct it in another VM. I don't want to modify its attributes because that object is a part of legacy application.

Standard Java serialization mechanism doesn't help. What other options do I have?

Update: The reason I'm asking the question is that I want to modify an existing Spring application. It called a bean's method in-process earlier but now I want to move the bean on a separate machine and use Spring remoting through HTTP invoker. And I have a problem with parameters that have transient fields that need to be passed to this method but not needed to be serialized in other parts of the app.

Answer 1

transient variables are supposed to be those that aren't serializable or are easily recalculated.

My first suggestion is to look for methods on this object to recalculate the transient fields.

Answer 2

I assume you cannot change the legacy code. In this case I think you will have to resort to going over the object fields with reflection and DataOutputStream.

Answer 3

Hmm - if an attribute is marked as transient, that means exactly that it's not mean to be considered part of the object's persistent state, e.g. for serialization. The fact that you want to do this at all is a code smell, and the correct solution is to stop those fields being transient.

Let's say though that for whatever reason you can't modify the target classes themselves. My first thought was that you could customise the serialisation by implementing readObject() and writeObject() methods, but that would also require changes to the target class.

In that case, you'll need to work with some kind of reflection-based or metadata-based API in order to do this. There are many libraries that will convert objects to and from XML or JSON or DB rows, etc. Your best bet would be to use one of these to convert the object to and from "hydrated" form (and likely you'll need to customise them, as any sane serialiser will ignore transient fields). Which one to pick depends on your current software stack, and your precise requirements.