The notions of "themes" and "templates" are at the core of the HTML Struts Tags provided by the framework.
A bit of code, usually written in FreeMarker, that can be rendered by certain tags (HTML tags)
A collection of templates packaged together to provide common functionality
See Struts Tags for more about the HTML and other tags provided by the framework.
How templates are loaded
How the template directories are loaded
How you can pick a theme when writing your results
How to create your own themes based on existing themes
More About Themes
A minimal theme with no "bells and whistles"
The default theme that uses common HTML practices
The xhtml theme re-implemented using strictly CSS for layout
A theme based on the xhtml theme that provides advanced AJAX features