public ActionErrors validate(ActionMapping mapping,HttpServletRequest request){
        ActionErrors errors=new ActionErrors();
        if(username.equals("")||username==null){
            errors.add("username",new ActionMessage("username"));
        }
        if(password.equals("")||password==null){
            errors.add("password",new ActionMessage("password"));
        }
        return errors;
    }

------解决方案--------------------
如果给你例子的话太长了
给你一个网站吧
http://www.blogjava.net/max

------解决方案--------------------
    @Override
    public void validate()  {
       System.out.println( " Calling validate() " );
        if ( ! (loc.equals(Locale.US) || loc.equals(Locale.CHINA)))  {
                   addFieldError( " loc " , getText( " validation.loc " ));
       }  
   }