public class SampleServlet extends HttpServlet {
      public void doPost(HttpServletRequest req, HttpServletResponse res)throws ServletException, IOException {
        ServletActions.valueOf("action1").execute(params);  //Invoking respective action
}
}

public enum ServletActions {

   ACTION_1 {
      //Do some actions
      //Notify `a` regarding the actions
      //Notify `b` regarding the action performed
      //Construct response json
   },

   ACTION_2 {
      //Do some actions
      //Notify `d` regarding the actions
      //Notify `e` regarding the action performed
      //Construct response json
   },

   ACTION_3 {
      //Do some actions
      //Notify `d` regarding the actions
      //Notify `b` regarding the action performed
      //Construct response json
   },

   ACTION_4 {
   },

   ACTION_5 {
   },

   ACTION_6 {
   },

   ACTION_7 {
   };
}

public enum ServletActionsNotifier {

       ACTION_1_NOTIFIER {
          public void sendNotification() {
               //Send agent notification
               //Send progress notification
          }
       },

       ACTION_2_NOTIFIER {
         public void sendNotification() {
               //Send task notification
               //Send progress notification
         }
       },

       ACTION_3_NOTIFIER {
          public void sendNotification() {
               //Send feed notification
               //Send success notification
         }
       },

       ACTION_4_NOTIFIER {
       },

       ACTION_5_NOTIFIER {
       },

       ACTION_6_NOTIFIER {
       },

       ACTION_7_NOTIFIER {
       };
      abstract void sendNotification();
    }