I don't know of a good java-centric book that is a well rounded networking book.
TCP/IP Sockets in Java by Calvert/Donahoo is a decent starter book. It covers basic java networking libraries, along with IO, threads and parsing and framing. But it lacks a serious discussion on the topic and has a little info on the underlying protocols. It is small, easy to read and cheap(<$20 US). A book like this might be a good starting point.
Probably the best introductory book is Unix Network Programming. It is a very solid computer science book, but is not overly difficult to read. It does require a working knowledge of C. The book covers the Berkley Sockets API which is used on most non-MS operating systems, and Windows API's are based on it. The book covers a good deal but doesn't get into more advanced topics.
"Should array indices start at 0 or 1? My compromise of 0.5 was rejected without, I thought, proper consideration."- Stan Kelly-Bootle