If you are looking for improving upon basics on networking it would be better if you look at books which cover basics of networking. Once you are comfortable with the basics of networking you can start with the networking section in Java tutorial and explore the appropriate Java libraries. Networking is an area of its own whose understanding is independent of any programming language.
That said, some of the networking books which I have found helpful are :
Internetworking with TCP/IP, Vol 1
by Douglas Comer
TCP/IP Illustrated Vol.1
by W.Richard Stevens
Computer Networks
by Andrew.S.Tanenbaum
