There is no explicit abstraction of the protocol under struts. Hence you have to specify explicit URLs in your config and a JSP files to change between protocols or manage this stuff your self.
<forward name="http-destination"
path="http://site:port/blah/blah.jsp"/>
<forward name="https-destination"
path="https://site:port/blah/blah.jsp"/>
Then in your form handler use something like:
return mapping.findForward(secureMode ? "https-destination" :
"http-destination");
Sadly you will probably have to change all the URLs when you move
between development, staging and production.