java - Dependency injection into scala objects (not classes)

Question

I have an import "import play.api.libs.ws.WSClient" which i want to use within my object

Object X {
...

}

But this doesn't seem to be available inside my object. I see that dependency injection is only available for classes. How do i get this to work?

Answer 1

Injecting a dependency into an object is impossible.

You have two options:

Ugly and deprecated: Access the injector via the global application:

val wsClient = Play.current.injector.instanceOf[WSClient]

Way to go if your code needs to live in an object: Pass the dependency in as a parameter. However this just defers the problem to the caller.

def myMethod(wsClient: WSClient) = // foo

If youre working with a legacy application where you have objects and need an injected dependency, I think one way to "improve" the situation and make a step into the right direction is to provide access to an injected class like so:

object MyObject {
  private def instance = Play.current.injector.instanceOf[MyObject]
  def myMethod(param: String): String =
    instance.myMethod(param)
}

class MyObject @Inject() (wsClient: WSClient) {
  def myMethod(param: String): String = 
   // foo
}

This allows legacy code to access the methods via object, while new code can inject the dependency. You may also annotate the method on the object as deprecated so that users know.