Failed startup of context com.google.appengine.tools.development.DevAppEngineWebAppContext

I am using Spring MVC,google app engine, admin sdk, cloud sql. I want to access (preferncesDao) dao class into Filter. Below is my filter

public class NameSpaceGoogleSecurityFilter implements Filter
{
    @Autowired
    IPreferencesDao preferncesDao;

    public void init( FilterConfig filterConfig ) throws ServletException{
          SpringUtils.init(filterConfig.getServletContext());
          preferncesDao = SpringUtils.getPreferncesDao();
   }
}

Below is my SpringUtils class.

public class SpringUtils {

   private static ApplicationContext appContext;

   private static IPreferencesDao preferncesDao = null;

   public static void init(final ServletConfig config) {
       init(config.getServletContext());
   }
   public static void init(final ServletContext context) {
      if(appContext==null){
        appContext =
            (ApplicationContext) context.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
      }
   }

   public static IPreferencesDao getPreferncesDao() {
      if(preferncesDao==null){
        preferncesDao=(IPreferencesDao) appContext.getBean("preferncesDao");
      }
     return preferncesDao;
   }

   protected SpringUtils() {
        throw new UnsupportedOperationException();
   }
}

When I start build process, It is throwing below exception

Failed startup of context com.google.appengine.tools.development.DevAppEngineWebAppContext
  java.lang.NullPointerException.  
  Nullpointer at line  preferncesDao=(IPreferencesDao) appContext.getBean("preferncesDao");

How can i resolve above error ? is it right way to get dao object into filter ? if not what is correct way.?