As far as I'm aware, there are no taglibs for mathematical operations in the Struts framework. You'll have to perform the operation between scriptlet tags, or (the better solution) is perform anything you need within the action that's the predecessor for your jsp page. You jsp should, in theory, not need to perform such calculations, merely present the results.
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com