title: protobuf serialization of language specific data structures
body: <p>Using google's <a href="http://code.google.com/p/protobuf/" rel="nofollow noreferrer">Protocul Buffers</a>, I have a service already written in Java which has its own data structures already. I'd like to use pb to delivering messages and I'm looking for a way to serialize the existing data structures that I have in Java to pb.
  I can start by defining all the data structures in pb from scratch, which is probably the right way to go but I'm too lazy.
  So, say I have a Person class in Java (or other supported languages) or a Plane class which has tens of attributes in it, is there a way to serialize that class to pb? Can I have a pb attribute of type Plane? (when Plane is not a pb, it's a Java class)</p>