：
There is no Action mapped for namespace / and action name HelloWorld. - [unknown location]
com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:186)
org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:41)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:494)
org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:419)
：
struts.xml /WEB-INF/classes ， 。
struts.xml ：<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd"> 。