Guice and Play2 Singleton from trait

Question

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.

Answer 1

正如@Tavian-Barnes 所指出的，解决方案是确保您具有以下导入：

import javax.inject.Singleton

Answer 2

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 .

Answer 3

使用下面的导入，而不是import javax.inject.Singleton

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

Answer 4

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