code: public static String getToken(HttpServletRequest request, String action)
      {
          FlowController flowController = PageFlowUtils.getCurrentPageFlow(request);
  
          if (flowController != null) {
              MappingAndController mac = getActionMapping(request, flowController, action);
              if (mac != null) return getToken(request, mac.mapping);
          }
  
          return null;
      }
docs: Get or generate a token used to prevent double submits to an action.  The token is stored in the session,
  and checked (and removed) when processing an action with the <code>preventDoubleSubmit</code> attribute
  set to <code>true</code>.