play.api.inject

ApplicationLifecycle

Related Doc: package inject

trait ApplicationLifecycle extends AnyRef

Application lifecycle register.

This is used to hook into Play lifecycle events, specifically, when Play is stopped. The reason Play only provides lifecycle callbacks for stopping is that constructors are considered the application start callback. This has several advantages:

- It simplifies implementation, if you want to start something, just do it in the constructor. - It simplifies state, there's no transitional state where an object has been created but not started yet. Hence, as long as you have a reference to something, it's safe to use it. - It solves startup dependencies in a type safe manner - the order that components must be started is enforced by the order that they must be instantiated due to the component graph.

Stop hooks are executed when the application is shutdown, in reverse from when they were registered. Due to this reverse ordering, a component can know that it is safe to use the components it depends on as long as it hasn't received a shutdown event.

To use this, declare a dependency on ApplicationLifecycle, and then register the stop hook when the component is started. For example:

import play.api.inject.ApplicationLifecycle
import javax.inject.Inject

class SomeDatabase @Inject() (applicationLifecycle: ApplicationLifecycle) {

  private val connectionPool = new SomeConnectionPool()
  applicationLifecycle.addStopHook { () =>
    connectionPool.shutdown()
  }

  ...
}
Source
ApplicationLifecycle.scala
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Abstract Value Members

  1. abstract def addStopHook(hook: () ⇒ Future[Unit]): Unit

    Add a stop hook to be called when the application stops.

    Add a stop hook to be called when the application stops.

    The stop hook should redeem the returned future when it is finished shutting down. It is acceptable to stop immediately and return a successful future.

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  4. def addStopHook(hook: Callable[Promise[Void]]): Unit

    Add a stop hook to be called when the application stops.

    Add a stop hook to be called when the application stops.

    The stop hook should redeem the returned future when it is finished shutting down. It is acceptable to stop immediately and return a successful future.

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