Guice injecting Generic type

Question

I'am trying to Inject generic type with Guice. I have Repository< T > which is located in the Cursor class.

public class Cursor<T> {

    @Inject
    protected Repository<T> repository;

So when I create Cursor< User >, I also want the Guice to inject my repository to Repository< User >. Is there a way to do this?

I do have one, but I have no idea how to inject it to generic, because there are some more repositories. — petomalina, Jul 09 '14 at 15:06

score 32 · Accepted Answer · edited Feb 03 '17 at 00:05

32

You have to use a TypeLiteral:

import com.google.inject.AbstractModule;
import com.google.inject.TypeLiteral;

public class MyModule extends AbstractModule {

  @Override
  protected void configure() {
    bind(new TypeLiteral<Repository<User>>() {}).to(UserRepository.class);
  }
}

To get an instance of Cursor<T>, an Injector is required:

import com.google.inject.Guice;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.TypeLiteral;

public class Main {

  public static void main(String[] args) {
    Injector injector = Guice.createInjector(new MyModule());
    Cursor<User> instance = 
        injector.getInstance(Key.get(new TypeLiteral<Cursor<User>>() {}));
    System.err.println(instance.repository);
  }
}

More details in the FAQ.

edited Feb 03 '17 at 00:05

dimo414

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answered Jul 09 '14 at 15:12

gontard

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I thought the same, but did you try that out? I got `Repository cannot be used as a key; It is not fully specified`. – steffen Jul 09 '14 at 15:17
I often use this kind of configuration without any problem. And i provide some links to the guice documentation – gontard Jul 09 '14 at 15:18
The thing is, I need the constructor to the UserRepository to be injected. So there's no way to call Guice.createInjector – petomalina Jul 09 '14 at 15:22
The entry point of guice is the injector. How do you want to use guice without it ? – gontard Jul 09 '14 at 15:23
The difference between the examples in the guice documentation and the problem here is (guice documentation) `Collection` vs. (here) `Collection`. While the former can be injected, the latter gives the error message above. So did you try it out with something like `Collection`? – steffen Jul 09 '14 at 15:25
@steffen In this case, @Gelidus needs to bind a `Repository` to a `UserRepository`. There is no need to bind a `Repository`. If you want to bind a `Collection` to an `ArrayList`, you could simply do `bind(Collection.class).to(ArrayList.class)`. – gontard Jul 09 '14 at 15:28
You're right, in my test scenario was a circular reference :-/ – steffen Jul 09 '14 at 15:34
i know this is old, but i have what really feels like the same problem here: http://stackoverflow.com/questions/40646780/dependency-injection-using-guice-with-the-dao-pattern and i'm struggling to figure it out. can anyone provide guidance? – Justin Nov 18 '16 at 02:49
What if I do not have an interface and implementation scenario? I just have one class, `Repository` and I need it to be injected in another class `Cursor`? I have bind them both like this: `bind(new TypeLiteral>() {});` `bind(new TypeLiteral>() {});` But I still get the `cannot be used as a key; It is not fully specified.` error – rrrocky Apr 04 '18 at 11:22
new to guice, if I bind Repository to Repository.class, then what would I do if I need to provide another type such as Repository, what should I bind to ? – user2386301 Aug 22 '20 at 21:12
My generic type is comes from a package-private class and is therefore invisible to the module. Anyway to bind this? – Cardinal System Mar 24 '23 at 13:45

Guice injecting Generic type

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