Action的mapping.findFoward(forwardName)必须要在struts-config.xml中的对应的action节点配置一个forward节点

比如说你有个SampleAction，在execute(ActionMapping mapping, ...)中写了句

return mapping.findForward("some_page");

那么你相应的在struts-config.xml中就必须有类似如下的配置：

<action ... type="org.someone.struts.action.SampleAction">

　　<forward name="some_page" path="/samplepages/some_page.jsp"></forward>

</action>