HK2 IterableProvider named method not finding Implementation

问题

I have a problem trying to inject a contract with two services bound to it.

I'm using Jersey, and extending ResourceConfig to configure my app, where I'm binding two different implementations (classes FooImpl1 and FooImpl2) to a same contract (interface Foo), ranking them differently. Each of these implementations is annotated with @Named and its name.

In one of my controllers I want to have access to both implementations, so I inject an IterableProvider<Foo> fooProvider.

If I do not specify anything, the implementation with the highest rank is injected always, which is what I want.

The problem appears when I want a concrete implementation, one of them. When I call fooProvider.named( nameOfTheClass ).get(), is returning me null, but if I iterate over the fooProvider, I can have access to both implementations, so they are injected.

Anybody has an idea of what could I be missing?

Thanks a lot for your help.

回答1:

Yeah so I'm not sure why it doesn't work with the @Named annotation value, as that's what's stated int the javadoc, but without the need for any annotations, we can configure the name when we do our bindings. We can do so with the named method.

register(new AbstractBinder(){
    @Override
    public void configure() {
        bind(Foo1Impl.class).named("foo1").to(Foo.class);
        bind(Foo2Impl.class).named("foo2").to(Foo.class);
    }
});

UPDATE

So the above solution has been tested. If you are having problems still, post a complete runnable example that demonstrates it not working, like below (which is working)

Interface and Implementations

public interface Greeter {
    String getGreeting(String name);
}

public class EnglishGreeter implements Greeter {
    @Override
    public String getGreeting(String name) {
        return "Hello " + name + "!";
    }
}

public class SpanishGreeter implements Greeter {
    @Override
    public String getGreeting(String name) {
        return "Hola " + name + "!";
    }
}

Resource

@Path("greeting")
public class GreetingResource {

    @Inject
    private IterableProvider<Greeter> greeters;

    @GET
    public Response getResponse(@QueryParam("lang") String lang,
                                @QueryParam("name") String name) throws Exception {

        Greeter greeter = greeters.named(lang).get();
        String message = greeter.getGreeting(name);
        return Response.ok(message).build();
    }
}

Binding. I did it in a Feature, but in a ResourceConfig, it's all the same.

@Provider
public class GreetingFeature implements Feature {
    @Override
    public boolean configure(FeatureContext context) {
        context.register(new AbstractBinder(){
            @Override
            public void configure() {
                bind(EnglishGreeter.class).named("english")
                        .to(Greeter.class).in(Singleton.class);
                bind(SpanishGreeter.class).named("spanish")
                        .to(Greeter.class).in(Singleton.class);
            }
        });
        return true;
    }  
}

Result

来源：https://stackoverflow.com/questions/29283176/hk2-iterableprovider-named-method-not-finding-implementation

标签

java

dependency-injection

jersey

jersey-2.0

hk2