title: display an error message on a jsp using controller
body: <p>hi i have to display an error message on a jsp using a controller</p>
  
  <p>this is the code of the controller</p>
  
  <pre><code>@RequestMapping(value = "/addUrl", method = RequestMethod.POST)
  public String addUrl(WebRequest request) {
  
      logger.info("Calling Add Filters in POST mode");
  
      String serverUrl = request.getParameter("serverUrl");
      logger.info("ServerUrl" + serverUrl);
  
      if(serverUrl!=null)
      {
          mongoService.setServerUrl(serverUrl);
      }
      else
      {
          //show message on UI if serverUrl is null
  
      }
  
      return "redirect:config.do";
  }
  </code></pre>
  
  <p>sorry to say but i am completely new to spring so dont know to do it??.thanks in advance</p>