code: public void notifyBeforeEvaluation(String expr) {
          if (getEvaluationListeners() == null)
              return;
          for (EvaluationListener listener: getEvaluationListeners()) {
              listener.beforeEvaluation(this, expr);
          }
      }
docs: Notifies the listeners before an EL expression is evaluated
  @param expr The EL expression string to be evaluated