Guice bind a class and its adapter - scala

Question

I would like implement a Guice module which binds an adapter to a named argument, but to create this adapter, it needs to instantiate another class, which also need injected arguments.
Here is the example in Scala:
trait Service
class UserService #Inject()(#Named(value = "foo") foo: String) extends Service
trait Adapter
class AdapterImpl(service: Service) extends Adapter
class AdapterRef(val adapter: Adapter)
class Module extends AbstractModule {
override def configure(): Unit = {
val fooValue = "bar"
bind(classOf[String])
.annotatedWith(Names.named("foo"))
.toInstance(fooValue)
val userService = new UserService(fooValue) //It should be instantiated by Guice somehow
bind(classOf[AdapterRef])
.annotatedWith(Names.named("userService"))
.toInstance(new AdapterRef(new AdapterImpl(userService))) //Thats kinda ok
}
}
Can someone point me to the right direction?
Thank you,
Gabor

Answer 1

You can use a Provides method within your module, which lets you remove the binding. This is my best effort at Scala so if the syntax is incorrect let me know.
#Provides() #Singleton() def provideAdapterRef(service: Service): AdapterRef = {
return new AdapterRef(new AdapterImpl(service))
}
Note the use of Singleton to imitate your examples use of toInstance. If you don't need it to always provide the same instance I would recommend removing the scope and letting it create a new one every time.
An alternative solution is to use a Provider. This requires you to keep a modified version of the binding in your module and create an extra class, but it can be a cleaner solution if your Provider is more complex.
//Can inject UserService as well, or provide annotations to configure which
//implementation of Service you get if you have more than one.
class UserServiceProvider #Inject()(service: Service) extends Provider[AdapterRef] {
override def get(): AdapterRef {
return new AdapterRef(new AdapterImpl(service))
}
}
Then you can change your binding in the module to
bind(classOf[AdapterRef])
.annotatedWith(Names.named("userService"))
.toProvider(classOf[UserServiceProvider])
.in(classOf[Singleton])
Here note the use of in(Singleton) to replicate your toInstance behavior.