CODEWITHSUNDEEP
scalaplayframeworkplayframework-2.0guice
Gleeb
Gleeb

Reputation: 11289

Guice and Play2 Singleton from trait

I am using Play with Scala and I am trying to create a singleton, and i want to inject it from its trait and not directly.

for example:

@ImplementedBy(classOf[S3RepositoryImpl])
trait S3Repository {
}
@Singleton
class S3RepositoryImpl extends S3Repository {
}

But this fails with error:

trait Singleton is abstract; cannot be instantiated

I have tried several combinations and they all produce the same.

I come from Spring background and its very natural there? am i missing something about how Guice handles this type of Injection?

Thanks.

Upvotes: 11

Views: 6921

Answers (4)

swapnil shashank
swapnil shashank

Reputation: 997

Import both Inject and Singleton.

import javax.inject.{Inject, Singleton}

Refrain from using:

import com.google.inject.{Inject, Singleton}

as play framework requires the javax import

Upvotes: 2

Ashish Pushp
Ashish Pushp

Reputation: 238

Use below import, instead of import javax.inject.Singleton

import com.google.inject.{Inject, Singleton}

Upvotes: 4

Chris Beach
Chris Beach

Reputation: 4392

As pointed out by @Tavian-Barnes, the solution is to ensure you have the following import:

import javax.inject.Singleton

Upvotes: 41

insan-e
insan-e

Reputation: 3921

I have here a "complete" working example, just hope that I'm not stating the obvious...

package controllers

import play.api._
import play.api.mvc._
import com.google.inject._

class Application @Inject() (s3: S3Repository) extends Controller {
  def index = Action {
    println(s3.get)
    Ok
  }
}

@ImplementedBy(classOf[S3RepositoryImpl])
trait S3Repository {
  def get: String
}

@Singleton
class S3RepositoryImpl extends S3Repository {
  def get: String = "bla"
}

Whenever you mark a class' constructor with @Inject the Guice will manage the injection of the instance itself. So, if you marked your class as @Singleton, Guice will create and will always give you just that one instance. Nobody can stop you from manually instantiating a class in your code... You can explore it in detail at Play.

Upvotes: 6

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