This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
I did a quick search of Struts 2.2.1 source and couldn't find any reference to a class named ClassPool.
If you just want to resolve the dependency, the class appears to originate here, but you should probably figure out where that dependency is coming from.