Servlet 3.1 is a relatively minor release included in Java EE 7. However, the Java EE foundational API still contains some very important changes. One such set of features are the security enhancements done in Servlet 3.1 such as the new deny-uncovered-http-methods option.
Servlet 3.1 co-spec lead Shing Wai Chan outlines the use case for the feature and shows you how to use it in a recent code example driven post. You can also check out the official specification yourself or try things out with the newly released Java EE 7 SDK.