This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
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Where did you find this example? It's sure looks wrong. The struts.xml file should be under the WEB-INF directory. Your helloworld.class file should be under classes, not lib. The path is case-sensitive, so I think CLASSES is wrong as well.
If you want a good example, several come with the Struts distribution, including a blank application that you can extend with your own code.