Dependency Injection to Play Framework 2.5 modules

问题

I have a module class with the following signature:

class SilhouetteModule extends AbstractModule with ScalaModule {

I would like to inject configuration:

class SilhouetteModule @Inject() (configuration: Configuration) extends AbstractModule with ScalaModule {

But it fails with the following error.

No valid constructors
Module [modules.SilhouetteModule] cannot be instantiated.

The Play documentation mentions that

In most cases, if you need to access Configuration when you create a component, you should inject the Configuration object into the component itself or...

, but I can't figure out how to do it successfully. So the question is, how do I inject a dependency into a module class in Play 2.5?

回答1:

There are two solutions to solve your problem.

First one (and the more straight forward one): Do not extend the com.google.inject.AbstractModule. Instead use the play.api.inject.Module. Extending that forces you to override def bindings(environment: Environment, configuration: Configuration): Seq[Binding[_]]. Within that method you could do all your bindings and you get the configuration inserted as a method-parameter.

Second one (and the more flexible one): Depending on your needs of the components you want to inject, you could define a provider for the component you want to bind. In that provider you could inject whatever you want. E.g.

import com.google.inject.Provider

class MyComponentProvider @Inject()(configuration:Configuration) extends Provider[MyComponent] {
    override def get(): MyComponent = {
        //do what ever you like to do with the configuration
        // return an instance of MyComponent
    }
}

Then you could bind your component within your module:

class SilhouetteModule extends AbstractModule {
    override def configure(): Unit = {
        bind(classOf[MyComponent]).toProvider(classOf[MyComponentProvider])
    }
}

The advantage of the second version, is that you are able to inject what ever you like. In the first version you get "just" the configuration.

回答2:

Change your constructor signature from:

class SilhouetteModule @Inject() (configuration: Configuration) extends AbstractModule with ScalaModule

to:

class SilhouetteModule(env: Environment, configuration: Configuration) extends AbstractModule with ScalaModule

see here for more info: https://github.com/playframework/playframework/issues/8474

来源：https://stackoverflow.com/questions/39863190/dependency-injection-to-play-framework-2-5-modules

标签

scala

playframework

dependency-injection