I\'m getting a little bit frustrated since I can\'t find out which variables I can access with the ${...}
syntax in a Struts tag, placed in a JSP page.
It should be placed in any of the page, request, session or application scopes using respectively JspContext#setAttribute(), ServletRequest#setAttribute(), HttpSession#setAttribute() or ServletContext#setAttribute(). You normally do that either directly or indirectly inside a Servlet. MVC frameworks do that indirectly, usually configureable by giving the model object a "request", "session" or "application" scope.
The Expression Language (EL) will access them using JspContext#findAttribute().
This all is by the way unrelated to Struts. It's just a legacy MVC framework which is built on top of the JSP/Servlet API. The <c:set>
is not a Struts tag as well, it's a JSTL tag.