code: public void sendError(int code,String message) 
          throws IOException
      {        
          setStatus(code,message);
          
          // Generate normal error page.
          HttpRequest request=getHttpRequest();
          
          // If we are allowed to have a body 
          if (code!=__204_No_Content &&
              code!=__304_Not_Modified &&
              code!=__206_Partial_Content &&
              code>=200)
          {
              if (getHttpContext()!=null)
              {   
                  Object o=
                      getHttpContext().getAttribute(HttpContext.__ErrorHandler);
                  if (o!=null && o instanceof HttpHandler)
                      ((HttpHandler)o).handle(request.getPath(), null, request, this);
              }
          }
          else if (code!=__206_Partial_Content) 
          {
              _header.remove(HttpFields.__ContentType);
              _header.remove(HttpFields.__ContentLength);
              _characterEncoding=null;
              _mimeType=null;
          }
          
          commit();
      }
docs: Send Error Response.