精通Struts基于MVC的Java Web设计与开发试验的一个小问题？

现在提示这个错误？
HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception javax.servlet.ServletException: Cannot retrieve mapping for action /HelloWord
org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:825)
org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:758)
org.apache.jsp.hello_jsp._jspService(hello_jsp.java:101)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause javax.servlet.jsp.JspException: Cannot retrieve mapping for action /HelloWord
org.apache.struts.taglib.html.FormTag.lookup(FormTag.java:810)
org.apache.struts.taglib.html.FormTag.doStartTag(FormTag.java:506)
org.apache.jsp.hello_jsp._jspx_meth_html_form_0(hello_jsp.java:308)
org.apache.jsp.hello_jsp._jspx_meth_html_html_0(hello_jsp.java:148)
org.apache.jsp.hello_jsp._jspService(hello_jsp.java:94)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)