This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
A ServletConfig object is used to serve initialization info to the Servlet. A ServletContext object is the one that's used by the Servlet at runtime to dynamically get handle to other context resources/objects. Both serve two different purposes.
You can theorotically, get a RD object from config too (see below), though it would actually access the context object for this