Why Can't show the errors generated by a ActionForm's validate method

[艳龙 周]

hi, I'm new to struts and I really can't find a way to solve the proplem.
plese help me. thank you so much.
Here is the proplem. I have a input.jsp,a ActionForm and a Action
public class HelloForm extends ActionForm
{
    private String name=null;
    
   public ActionErrors validate(ActionMapping map,HttpServletRequest req)
    {
        ActionErrors err=new ActionErrors();
        if(name.length()<1||name==null)
            err.add("nouser" ,new ActionMessage("jsp.no.user"));
      
        return err;
    }
when name!=null &&name.lengh>1 ,everything is normal ,the Action goto the jsp 
page I expect
but  when (name.length()<1|| name==null) is true,I think it should go to the 
input.jsp,and use <html:errors> to display the AcionMessage("jsp.no.user") 
..But the proplem comes out:

java.lang.ClassCastException    
org.apache.struts.taglib.html.ErrorsTag.doStartTag(ErrorsTag.java:215)  
org.apache.jsp.input_jsp._jspx_meth_html_errors_0(input_jsp.java:349)   
org.apache.jsp.input_jsp._jspx_meth_html_html_0(input_jsp.java:133)     
org.apache.jsp.input_jsp._jspService(input_jsp.java:87) 
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)    
org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1069) 
org.apache.struts.action.RequestProcessor.internalModuleRelativeForward(RequestProcessor.java:1012)
     
org.apache.struts.action.RequestProcessor.processValidate(RequestProcessor.java:980)
        
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:255)    
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482) 
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)   
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)    
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)please help me~






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