4.1.6. Running Code on Startup
Sometimes you need to run some code on the application startup, at the moment when all application functionality is already initialized and ready to work. For this, you can use AppContext.Listener.
In this section we demonstrate how to dynamically register an entity listener on application startup. Consider the following task: a project has an
Employee entity that is linked one-to-one to the platform’s
name attribute of the
User entity is changed, for example, through a standard user management screen, the
name attribute of the related
Employee should change as well. This is a common task for "denormalized" data, which is typically solved using entity listeners. Our case is more complicated, since we need to track changes of the platform’s
User entity, and thus we cannot add an entity listener using the @Listeners annotation. So we will add a listener dynamically using the
EntityListenerManager bean on application start.
As a result, the
applicationStarted() method of the
AppLifecycle bean will be invoked on the middleware block startup. This method registers the
sample_UserEntityListener bean as an entity listener for the
onBeforeUpdate() method of the
UserEntityListener class will be invoked every time before the changes in the
User instances are saved to the database. The method checks if the
name attribute exists among the updated attributes. If yes, a related
Employee instance is loaded and its
name is updated with the new value.