playframework Dependency Injection - Scala Defining custom bindings in a Module

Example

Basic usage of dependency injection is done by the annotations. When you need to tweak things a little bit, you need custom code to further specify how you want some classes to be instantiated and injected. This code goes in what is called a Module.

import com.google.inject.AbstractModule
// Play will automatically use any class called `Module` that is in the root package
class Module extends AbstractModule {

  override def configure() = {
    // Here you can put your customisation code.
    // The annotations are still used, but you can override or complete them.
    
    // Bind a class to a manual instantiation of it
    // i.e. the FunkService needs not to have any annotation, but can still
    // be injected in other classes
    bind(classOf[FunkService]).toInstance(new FunkService)

    // Bind an interface to a class implementing it
    // i.e. the DiscoService interface can be injected into another class
    // the DiscoServiceImplementation is the concrete class that will
    // be actually injected.
    bind(classOf[DiscoService]).to(classOf[DiscoServiceImplementation])

    // Bind a class to itself, but instantiates it when the application starts
    // Useful to executes code on startup
    bind(classOf[HouseMusicService]).asEagerSingleton()
  }

}