TCP/IP stack implemented with Java

I just wonder if anyone in this world has ever inplemented the TCP/IP stack with Java. Maybe that's too slow compared with C.
And I really find the TCP/IP related Java classes have much fewer arguments than the corresponding C methods, thus much simpler and lacking full functions.
Is it possible to implement TCP/IP stack in a way that you can dynamically configure proper parameters, such as TIME_WAIT, sendbuffer, recvbuffer, according to the network conditions (eg. too congested at the moment).
Anyone has ever heard about that??
I'm thinking about that seriously now.