EL 3 is one the APIs that has gone through a major overhaul in Java EE 7. In fact, EL is now finally a specification on its own right after long being an important API for JSTL, JSP, JSF and CDI. Most folks in the ecosystem are just beginning to realize the full significance of this. EL 3 opens up the possibility of using the power of a standard expression language in new and innovative ways in frameworks and applications much like the way Bean Validation 1.1 now utilizes EL. Just some of the changes in EL 3 includes a stand-alone API, powerful new operators, static field and method references, lambda support (essentially ahead of Java SE 8) and much, much more. Servlet 3.1 specification lead Shing Wai Chan handily demonstrates how some of the EL 3 features fit together in an excellent blog post. The code example calculates a standard deviation three different ways using various EL 3 features inside a Servlet. The blog post is really a great place to get started with learning EL 3. You can also check out Ed Burns and Kin-man Chung's JavaOne 2013 session on EL 3 via Parleys:
The slide deck for the session is available on the JavaOne content builder. It may be particularly interesting to relate the content of the slide deck back to Shing Wai Chan's blog entry.