Cocoon and Struts together? This idea is developed here.
My very humble opinion: Struts is very good for decision making inside the web application. Cocoon is good for internal data manipulation and output. The duo is simply great!
Cocoon Plugin for Struts 1.1+ is a project that embeds Cocoon into Struts as a plugin. After a request is processed by Struts, it can be forwarded to Cocoon to be displayed. The plugin allows regular Struts forwards and Cocoon forwards to live side-by-side. The latest version is based on Cocoon 2.1.