how to know that an app was launch from a click to a notification in the system tray?

I sent an alert notification, the app was not running or in background, so the alert terminate in the system tray. Then later the user click on this notification and my app is launched. How from my app know that it's was launched from a click on a notification alert in the开发者_JAVA技巧 system tray and how to retrieve the informations regarding this notification? Also I m using Firebase cloud messaging.