When you say J2EE, which technologies in particular are you referring too? I ask the question because the spec actually includes JSP, Servlets, JMS, EJB and probably other things I'm leaving out. People tend to mean different things when they talk about J2EE apps. For example, a number of people I know equate it to EJB stuff only.
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Struts is an application development framework that conforms to the Model View Controller architecture. It uses custom tags, a validation framework, global exception handling, etc. So, if you're writing apps and you want a ready made framework, it may or may not be to your liking. I can't say that I've done much with it. I only know this much because I've come across it in reading, most recently in the book "Head First Servlets and JSP".