Learning
Struts is non-trivial because it draws on a bunch of different technologies. First and foremost, use the
Java Tutorial. You said you had been through the "first cup" section. Don't miss Learning the Java Language and Essential Java Classes trails. Those trails give you a good cross-section of the Java API. You can skip the GUI-oriented trails since you are doing server-side programming. Next, consult the
Java 2 Enterprise Edition Tutorial for the web-specific technologies. There's a lot on web services (don't bother right now) and XML (get the basics of what XML is so you can work with Struts config files). Chapter 11 is where things get relevant.
Servlets and
JSP's are what Struts is made of.
You should be done around chapter 16 unless you are doing internationalization or serious
EJB programming. Next you can get to what you want to know, how to use Struts to get things done. I worked with Struts over the summer and the on-line documentation was scant, so get the Oreilly "Programming Jakarta Struts" book by Cavaness. It has a lot of good background information on how all these technologies work together.
Good luck.