Scala Play Framework - controller as class or singleton

Question

I'm trying Play 2.4.2 for Scala and I'm not clear whether controllers should be defined as classes or singletons. The docs state:

A Controller is nothing more than a singleton object that generates Action values.

However the code sample shows:

class Application extends Controller { ... }

To further complicate things, intellij gives me a warning if I define a class:

intellij warning

However I get a compilation error (but no warning) if I use a singleton:

package controllers

import play.api._
import play.api.mvc._

object Application extends Controller { ... }

Error:(6, -1) Play 2 Compiler: /Users/Toby/IdeaProjects/play-scala/conf/routes:6: type Application is not a member of package controllers

Which approach is correct?

First check the controller is in the required package, then either define it as singleton object Application extends Controller, or as class if you need Dependency Injection. — cchantep

dwickern dwickern · Accepted Answer · 2015-07-11T15:20:34

Your controllers should be objects if you use the static router. The static is the default router in Play 2.4 and has the same behavior from Play 2.3 and before.

You can convert your controllers to classes if you use the injected router which is new in Play 2.4. You need to enable the injected router in your build.sbt:

routesGenerator := InjectedRoutesGenerator

Update: the injected router is now the default in Play 2.5

Scala Play Framework - controller as class or singleton

1 Answers