Both java and c# support regex. The first time I learned regex, was through perl, but that was a while back; Nowadays, regex is commonly supported in lots of languages.

To answer your question, I think it doesn't matter whether you use web site, or book. My suggestion is to learn it in a more systematic way initially (book or web site) - that probably will take you couple of hours or longer depending on your learning style. After that mainly rely on web sites and manuals.