在模块中定义自定义绑定

依赖注入的基本用法是通过注释完成的。当你需要稍微调整一下时，你需要自定义代码来进一步指定你希望如何实例化和注入某些类。这段代码放在所谓的模块中。

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()
  }

}