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5. Embedding Play

§Embedding a Netty server in your application

While Play apps are most commonly used as their own container, you can also embed a Play server into your own existing application. This can be used in conjunction with the Twirl template compiler and Play routes compiler, but these are of course not necessary, a common use case for embedding a Play application will be because you only have a few very simple routes.

The simplest way to start an embedded Play server is to use the NettyServer factory methods. If all you need to do is provide some straightforward routes, you may decide to use the String Interpolating Routing DSL in combination with the fromRouterWithComponents method:

import play.core.server._
import play.api.routing.sird._
import play.api.mvc._

val server = NettyServer.fromRouter() {
  case GET(p"/hello/$to") => Action {
    Results.Ok(s"Hello $to")
  }
}

By default, this will start a server on port 9000 in prod mode. You can configure the server by passing in a ServerConfig:

import play.core.server._
import play.api.routing.sird._
import play.api.mvc._

val server = NettyServer.fromRouter(ServerConfig(
  port = Some(19000),
  address = "127.0.0.1"
)) {
  case GET(p"/hello/$to") => Action {
    Results.Ok(s"Hello $to")
  }
}

You may want to customise some of the components that Play provides, for example, the HTTP error handler. A simple way of doing this is by using Play’s components traits, the NettyServerComponents trait is provided for this purpose, and can be conveniently combined with BuiltInComponents to build the application that it requires:

import play.core.server._
import play.api.routing.Router
import play.api.routing.sird._
import play.api.mvc._
import play.api.BuiltInComponents
import play.api.http.DefaultHttpErrorHandler
import scala.concurrent.Future

val components = new NettyServerComponents with BuiltInComponents with NoHttpFiltersComponents {

  lazy val router = Router.from {
    case GET(p"/hello/$to") => Action {
      Results.Ok(s"Hello $to")
    }
  }

  override lazy val httpErrorHandler = new DefaultHttpErrorHandler(environment,
    configuration, sourceMapper, Some(router)) {

    override protected def onNotFound(request: RequestHeader, message: String) = {
      Future.successful(Results.NotFound("Nothing was found!"))
    }
  }
}
val server = components.server

In this case, the server configuration can be overridden by overriding the serverConfig property.

To stop the server once you’ve started it, simply call the stop method:

server.stop()

Note: Play requires an application secret to be configured in order to start. This can be configured by providing an application.conf file in your application, or using the play.http.secret.key system property.

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