code: protected String getFieldKey(Field field, Class<? extends ActionBean> actionBeanClass) {
          // Use key attribute if it is defined.
          String sessionKey = ((Session)field.getAnnotation(Session.class)).key();
          if (sessionKey != null && !"".equals(sessionKey)) {
              return sessionKey;
          }
          else {
              // Use default key since no custom key is defined.
              return actionBeanClass + "#" + field.getName();
          }
      }
docs: Returns session key under which field should be saved or read.
  @param field Field.
  @param actionBeanClass Action bean class.
  @return Session key under which field should be saved or read.