I am now working on a legacy application that is written with Struts 1.1. I first worked with Struts back in early 2002 while I was a junior developer at Iowa Foundation for Medical Care (now called Telligen). At the time we were JSP code with lots a scriplets calling stored procedures on the database. A co-worker Bryan Seaton started playing with Struts and then we integrated into the application we were working on at the time. The Struts Framework: Practical Guide for Java Programmers is a great starting guide. It is not too thick and weighty like many software books.
The Struts Framework is a Model View Controller pattern framework. The idea with this pattern design is to break up all the work. The view or in this case the JSP will not have any business logic. We were putting everything in our JSPs back at IFMC. Breaking this all out made sense but, took some time to get used to as any change does. The Model is where you move your business logic or in Struts terms these are called the Action classes. When you separate these into there respective classes you achieve what we call in the software world loose coupling.
I remember reading this book and a few others back when I first encountered Struts. The author Sue Spielman describes this book as focused on getting you working quickly. She did a good job of eschewing the normal bloat in many software books that cover a lot but don’t do many of those items justice.