to describe Struts parts within your UML models you should use a UML Profile (extension mechanism). The best way is to use an "agnostic" profile that is not strictly dedicated to Struts. The ideal profile is one that manages the underlying concepts of what you need to describe. The mapping between your model and Struts files can be done by a generator.
An example of such profile and generator is provide by Mia-Software
and can be found here :http://www.mia-software.com/index.php?lang=en&theme=sol-boosters-j2ee-struts