ridepublic void addApplicationListener(ApplicationListener<?> listener) { ? ?synchronized (this.retrievalMutex) { ? ? ? ?// Explicitly remove target for a proxy, if registered already, ? ? ? ?// in order to avoid double invocations of the same listener. ? ? ? ?Object singletonTarget = AopProxyUtils.getSingletonTarget(listener); ? ? ? ?if (singletonTarget instanceof ApplicationListener) { ? ? ? ? ? ?this.defaultRetriever.applicationListeners.remove(singletonTarget);