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.
I don't know much about struts 1.x, but the documentation says that if you return false from the requestPreprocess method, then the request processing will halt. So your class looks fine to me. I found two ways of configuring custom controller
the one that you are using.
The only point that might you maybe doing wrong is where you are declaring that element. I found that it must be declared after all action elements (usually deployment fails if there is anything wrong with xml configuration files like order of elements so I'm not sure if that's the cause)...