Is it safe to assume Spring ApplicationContext is initialized only once?

We have built a messaging server using PubNub which listens for chat messages from Android device. For this, our J2EE based spring, we have created a Pubnub listener (which is basically a listening socket) as follows. Since this needs to be created only once and at a application startup, we are using ContextRefreshedEvent for the same.

I am particularly doubtful about the use isContextLoaded variable since we are observing WTF: Not initialising incoming listener logs in our server randomly which I believe should not be there since context is initialised only once.

public class IncomingListener implements ApplicationListener < ContextRefreshedEvent > {     

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {

        private static volatile boolean isContextLoaded = false;

        @Autowired
        ServletContext application;

        synchronized(IncomingListener.class) {

            if (isContextLoaded) {
                System.out.println("WTF: Not initializing incoming listener");
                return;
            }
            try {
                initialiseIncomingListener();
                isContextLoaded = true;
            } catch (JSONException e) {
                e.printStackTrace();
            } catch (AkoshaException e) {
                e.printStackTrace();
            }

        }
    }

    private void initialiseIncomingListener()
    {
            // Initialize our Pubnub Listener

        pubnub.subscribe(serverchannel, new Callback() {

            // Subscribe to pubnub
                });
    }
}