Articles and Books:

Courtois, T. (1998) Java Networking and Communications, Prentice Hall , Palo Alto, CA.
(Order from amazon , order from Barnes and Noble , compare at bigwords , compare at CampusBooks4Less , order from Chegg , or search eFollett )

Harold, E.R. (1998) Java Network Programming, O'Reilly and Associates , Sebastopol, CA.
(Order from amazon , order from Barnes and Noble , compare at bigwords , compare at CampusBooks4Less , order from Chegg , or search eFollett )

McCarty, B. and L. Cassady-Dorion (1999) Java Distributed Objects, SAMS , Indianapolis, IN.
(Order from amazon , order from Barnes and Noble , compare at bigwords , compare at CampusBooks4Less , order from Chegg , or search eFollett )

WWW Pages: There are many good WWW pages devoted to Java network programming, including the following:

Java Tutorial

RMI
TCP

UDP
URLs&HTTP