How do I load configuration file on startup - scala

Question

I have application.conf file for my Scala program in main/resources. I load the configuration file using Config.load(). It is all working. But my config loading code is inside my service class. I want something like when program starts then first thing it doing is loading configuration. Then I want to use DI to pass this around.
This is easy in Scala Play because I just write Module class and specify in config file. Play then loads my config at start up. But how can I do this with non-Play project - just plain scala program.

Answer 1

Play uses Guice out-of-the-box for dependency injection, so you could consider using the same.
Here is an example of how guice can be used to inject configuration into services:
package example
import com.google.inject.{AbstractModule, Guice, Inject, Injector, Provides, Singleton}
import com.typesafe.config.ConfigFactory
import scala.jdk.CollectionConverters._
case class Config(foo: String, bar: String)
class Module extends AbstractModule {
#Provides
#Singleton
def getConfig: Config = {
val conf = ConfigFactory.load()
Config(
conf.getString("foo"),
conf.getString("bar")
)
}
}
class QuxService #Inject()(config: Config) {
println(config)
}
object ConfigInjectionExample extends App {
val injector: Injector = Guice.createInjector(List(new Module).asJava)
injector.getInstance(classOf[QuxService])
}
which outputs
Config(hello,world)
given the following resources/application.conf
foo="hello"
bar="world"
and the following dependencies
libraryDependencies += "net.codingwell" %% "scala-guice" % "4.2.6",
libraryDependencies += "com.typesafe" % "config" % "1.3.4"