How to handle datagrampackets on receiving side

I am trying to develop a Java networking application (using UDP) in which different types of data (different object types) need to be send, as datagrampackets, from the client to the server. I am wondering how I should handle these objects at the receiving side. How can I determine the object type at the receiving side just by the bytes that are received. Are there any design patterns which I should look for when implementing a packet handler?

Regards