Guice generics - how can I make it less ugly?

Question

I have an interface Producer<T> and a concrete FooProducer that implements Producer<Foo>. Binding this in guice looks ugly as sin:

bind(new TypeLiteral<Producer<Foo>>() {}).to(FooProducer.class);

I have lots of these such bindings. I have tried the following:

static <T> TypeLiteral<Producer<T>> producer() {
    return new TypeLiteral<Producer<T>>(){};
}

With calls made in this way:

bind(ContainingClass.<Foo>producer()).to(FooProducer.class);

But it gives an error along the lines of Producer<T> is not specific enough....

Am I going about this in the wrong way?

Answer 1

I believe that due to how TypeLiterals work, you have to actually write new TypeLiteral<Producer<Foo>>(){} or the necessary type information will not be available. They utilize the fact that a class that has fully specified its generic types can have information on those types retrieved. When you write new TypeLiteral<Producer<T>>(){}, you aren't specifying what T is, so that information isn't available.

It's subjective, but I don't think creating a type literal looks too ugly, considering what it does.

As an aside, I don't know what your Producer interface does, but if it is just used for producing instances of T (with a method that takes no arguments), you could use Guice's Provider interface instead. Then you just have to do:

bind(Foo.class).toProvider(FooProvider.class);

And you can inject a Foo or a Provider<Foo> anywhere.

Answer 2

You can save 8 characters by typing new Key<Producer<Foo>>(){} rather than new TypeLiteral<Producer<Foo>>(){}. Or by using the equivalent @Provides method:

@Provides
public Producer<Foo> provideFooProducer(FooProducer fooProducer) {
  return fooProducer;
}

Answer 3

Instead of

bind(new TypeLiteral<Producer<Foo>>() {}).to(FooProducer.class);

try a convenience method like

static <T> Key<Producer<T>> producerOf(Class<T> type) {
  return (Key<Producer<T>>)Key.get(Types.newParameterizedType(Producer.class,type));
}

and then in your module

bind(producerOf(Foo.class)).to(FooProducer.class);

That unchecked cast should be safe. Key is com.google.inject.Key and Types is com.google.inject.util.Types.

good luck