Blackcat

Lightweight dependency injection library for Java

Blackcat was developed while working on a 2D top-down game. Requirements were as follows:

• no external dependencies
• no component scanning
• no code generation, no byte code modification, no configuration files
• no black magic, simple to use and fast

It can do two things:

• annotation based field injections
• invoke post construction callbacks

To get the gist of this library, check out the unit tests.
Please note that cyclic dependencies are not resolved by design.

Simple example for building a band consisting of guitar and bass:

public class Band {
	@Inject
	private Guitar guitar;

	@Inject
	private Bass bass;

	public Band() {
	}
}

public class Guitar {
	public Guitar() {
	}
}

public class Bass {
	public Bass() {
	}
}

Injector injector = Injector.getInjector();

// declare DI components
injector.defineComponent(Band.class, Band::new);
injector.defineComponent(Guitar.class, Guitar::new);
injector.defineComponent(Bass.class, Guitar::new);

// get the band together
Band band = injector.getComponent(Band.class);

Basic component definition:

   defineComponent(Class<T> type, Provider<T> provider) 

A provider is as simple as this:

public interface Provider<T> {
	T provide();
}

It is up to you to create, handle or store component instances.

In case you need to do some post-constructor initialization, you can annotate a method with PostConstruct. This is typically necessary for init code that requires all injections to be available.

   @PostConstruct
   private void initializeMe() {
      // all injections have been set here
   }

To have multiple different components of the same class, components can be named.

public class Band {
   @Inject("stratocaster")
   private Guitar strat;

   @Inject("telecaster")
   private Guitar tele;
}

injector.defineComponent(Guitar.class, "stratocaster", Guitar::new);
injector.defineComponent(Guitar.class, "telecaster", Guitar::new);