Create Guice dependency injection binding in Scala function - scala

Question

I want to bind a certain class, lets call it injected either to its real implementation real or to its mock.
Also side effects should happen and therefor a function would be preferable to encapsulate this work.
Doing that outside of a function is known. But that also requires the side effects to be coded multiple times
The functionality iam looking for could be outlined as this (none working approach!)
private def bindMocksOptional(configSettingKey: String, injected: Class[_], real: Class[_] , mock: Class[_]) {
configuration.getOptional[Boolean](configSettingKey) match {
case Some(true) => {
bind(injected).to(mock)
val message = s"Using a mock (${mock.getCanonicalName})for ${injected.getCanonicalName}"
Logger.warn(message)
println(Console.MAGENTA + message)
}
case _ => bind(injected).to(real)
}
}
The function should take the outlined types as parameters, look up some config settings and based on those bind either to mock or real implementation.

Answer 1

You can use Provider:
import com.google.inject.{AbstractModule, Guice, Inject, Provider}
class Configuration {
def getOptional[T](key: String): Option[T] = None
}
trait DatabaseClient
class DatabaseClientMock extends DatabaseClient
class DatabaseClientReal extends DatabaseClient
// ---
// 1. Define Guice Provider:
class DatabaseClientGuiceProvide #Inject()(configuration: Configuration)
extends Provider[DatabaseClient] {
override def get(): DatabaseClient = {
configuration.getOptional[Boolean]("mock") match {
case Some(true) =>
println("used mock")
new DatabaseClientMock
case _ =>
println("used real")
new DatabaseClientReal
}
}
}
class MainModule extends AbstractModule {
override def configure(): Unit = {
// 2. Bind dependencies of provider
bind(classOf[Configuration]).toInstance(new Configuration)
// 3. Bind provider
bind(classOf[DatabaseClient])
.toProvider(classOf[DatabaseClientGuiceProvide])
}
}
// 4. Test it:
object GuiceMain extends App {
val module = Guice.createInjector(new MainModule)
println(module.getInstance(classOf[DatabaseClient]))
}