I don't know how close java gets to the real meat and bones with TCP. I
have a sneaking suspicion that Java has to hold your hand to make sure
you do it all right.

Also I don't know exactly what you are trying to do in this whole
concept of "Anti-DoS" systems. Hiding the transmitting IP in a TCP
transmittion is realy only going to do two things.

One: Send harmless replys to a third party.
Two: Send not-so harmless messages to people.

If you want to know how to ninja the IP packet  have a look at the open
source routing protocols for Unix.