Apache Struts 2 Documentation
Why does FreeMarker complain that there's an error in my user-directive when I used JSP Tag
To use JSP Tags with our FreeMarker templates, the jspSupportServlet needs to be loaded through the web.xml.
web.xml
The servlet element registers the JspSupportServlet and loads it on startup. FreeMarker obtains the information it needs to render JSP tags from the servlet instance.