谁帮我看看这个500错误是怎么回事？
用DAO模式struts+hibernate做的一个用户登陆 结果出了这个500错误 



HTTP Status 500 - 

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type Exception report 

message 

description The server encountered an internal error () that prevented it from fulfilling this request. 

exception 

org.apache.jasper.JasperException: Exception in JSP: /login.jsp:28 

25: </logic:equal> 
26: </logic:present> 
27: <br> 
28: <html:form action="login.do" method="post"> 
29: 用户ID：<html:text property="id"/><br> 
30: 密 码：<html:password property="password"/><br> 
31: <input type="hidden" name="status" value="login"> 


Stacktrace: 
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:506) 
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377) 
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314) 
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:802) 


root cause 

javax.servlet.ServletException: Cannot retrieve mapping for action /login 
org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:843) 
org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:776) 
org.apache.jsp.login_jsp._jspService(login_jsp.java:90) 
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:802) 
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:334) 
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314) 
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:802) 


root cause 

javax.servlet.jsp.JspException: Cannot retrieve mapping for action /login 
org.apache.struts.taglib.html.FormTag.lookup(FormTag.java:753) 
org.apache.struts.taglib.html.FormTag.doStartTag(FormTag.java:443) 
org.apache.jsp.login_jsp._jspx_meth_html_form_0(login_jsp.java:272) 
org.apache.jsp.login_jsp._jspx_meth_html_html_0(login_jsp.java:129) 
org.apache.jsp.login_jsp._jspService(login_jsp.java:81) 
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:802) 
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:334) 
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314) 
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:802) 


note The full stack trace of the root cause is available in the Apache Tomcat/5.5.20 logs. 


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Apa