How to add 'init' and 'destroy' like methods in scala play webapp? - scala

Question

I am very new to Play, I am writing a webapp using scala, in which I wish to implement the following functionality (Play version - 2.3.9):
When the application runs for the first time, five separate variables are to be read from a file (or a DB - this is yet to be decided).
These variables can be globally interfered with and updated while the app runs.
When the app shuts down, the file (or DB) is to be saved with the latest values for these variables.
I need to define sort of java servlet-like init and destroy functionalities to achieve this task. Could somebody guide me on how to achieve this?

Answer 1

Based on play 2.3.9 documentation you should define your hooks via the GlobalSettings:
import play.api._
object Global extends GlobalSettings {
override def onStart(app: Application) {
Logger.info("Application has started")
}
override def onStop(app: Application) {
Logger.info("Application shutdown...")
}
}
But I recommend to move to a newer version >= 2.4, there the GlobalSetting was deprecated, and so the way to add start and end hooks was changed.
In order to define a "start hook" you can add your own Guice module to the application configuration, there you can write what ever you need to heppen when the application starts.
And in order to add a "stop hook" you should use ApplicationLifecycle, see here more.
import scala.concurrent.Future
import javax.inject._
import play.api.inject.ApplicationLifecycle
#Singleton
class MessageQueueConnection #Inject() (lifecycle: ApplicationLifecycle) {
val connection = connectToMessageQueue()
lifecycle.addStopHook { () =>
Future.successful(connection.stop())
}
//...
}