This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Knowing Struts will probably help a little, because Struts covers a lot of the same ground that Stripes covers. So you'd be familiar with what such a framework can do for you, even if Struts goes about it in a different way. It's not required in any way, though.