Spring MVC 4显示错误消息

Question

我正在尝试显示和错误消息，如果登录时出错，我无法弄清楚如何做到这一点。这是控制器：

parentalControlInteractor.isPinSet()
            .subscribeOn(Schedulers.io())
            .delay(10000,TimeUnit.MILLISECONDS)
            .repeat()
            .doOnError(throwable -> {
                Timber.e(throwable,"Error getting if Pin is set");
                throwable.printStackTrace();
            })
            .subscribe(isPinSet -> {
                this.isPinSet = isPinSet;
                Timber.d("Pin is set = " + isPinSet.toString());
                });

jsp中的errorMessage为null。任何帮助将不胜感激。