How to reconstruct an object from byte[] not created from ObjectOutputStream?

But this method is tedious and I was wondering if there is an easy way out?

Not that I'm aware of. But if you find yourself writing the same code multiple times, you may well find that if you extract some helper methods it actually becomes pretty simple. Yes, you'll need to call a method to read each field value... but the code should end up being easy to read and understand, and not rely on anything magical.

You could do all of this with reflection, possibly using annotations to specify the order in which fields have been serialized etc. But that's likely to be a lot of code to write - unless you've got a lot of different types to deserialize, it will probably be more code - and more complicated code - than the "dumb but straightforward" approach.

I hope the format of the bytes from the C side of things is well-specified though: if it's basically just dumping the in-memory representation, that can end up being pretty fragile in the face of change.