Binding generics with wildcard in Guice

Question

I'm trying to bind a Class<? extends SuperClass> to SubClass.class, but I cannot find anything proper.

Actually my binding needs to be in a Set<Class<? extends SuperClass>>, so I've tested both the normal binding and the multibinding, but I can't have any of them working properly. I think I correctly followed this question: Using Guice, how can I inject a bounded-wildcard class? But I'm not really sure since my test doesn't pass.

import static java.util.Collections.*;
import static org.junit.Assert.*;
import java.util.Set;
import org.junit.Test;
import com.google.inject.*;
import com.google.inject.multibindings.Multibinder;

public class GuiceWildcardTest {

    @Test public void binderShouldBindClassWithWildcard() {
        Guice.createInjector(new AbstractModule() {
            @Override protected void configure() {
                bind(new TypeLiteral<Class<? extends SuperClass>>() {}).toInstance(SubClass.class);
                ClassHolder holder = new ClassHolder();
                requestInjection(holder);
                assertEquals(SubClass.class, holder.type);
            }
        });
    }

    @Test public void multibinderShouldBindSetOfClassesWithWildcard() {
        Guice.createInjector(new AbstractModule() {
            @Override protected void configure() {
                Multibinder.newSetBinder(binder(), new TypeLiteral<Class<? extends SuperClass>>() {}).addBinding().toInstance(SubClass.class);
                SetHolder holder = new SetHolder();
                requestInjection(holder);
                assertEquals(singleton(SubClass.class), holder.types);
            }
        });
    }

    static class SuperClass {}

    static class SubClass extends SuperClass {}

    static class ClassHolder {
        @Inject Class<? extends SuperClass> type;
    }

    static class SetHolder {
        @Inject Set<Class<? extends SuperClass>> types;
    }
}

I don't _think_ you mean `TypeLiteral>`, but instead `TypeLiteral extends Superclass>`. — Louis Wasserman, Jul 31 '12 at 21:19
I don't know: I want a set of classes, defined just like in the class SetHolder of my example. I don't want a set of instances. — Olivier Grégoire, Jul 31 '12 at 21:50
Okay, I get it. If I wait fully for the injector to be created, it's okay. But if I `requestInjection(a)` my object and directly check for the injectee, then it fails. — Olivier Grégoire, Aug 01 '12 at 10:08

score 1 · Accepted Answer · answered Aug 01 '12 at 10:13

My problem was that I didn't wait for the injector to be complete. requestInjection() does the trick, but after the Injector is created, so not immediately after the call to requestInjection().

This code works:

import static java.util.Collections.*;
import static org.junit.Assert.*;

import java.util.Set;

import org.junit.Test;

import com.google.inject.AbstractModule;
import com.google.inject.Guice;
import com.google.inject.Inject;
import com.google.inject.TypeLiteral;
import com.google.inject.multibindings.Multibinder;

public class GuiceWildcardTest {

    @Test public void binderShouldBindClassWithWildcard() {
        final ClassHolder holder = new ClassHolder();
        Guice.createInjector(new AbstractModule() {
            @Override protected void configure() {
                bind(new TypeLiteral<Class<? extends SuperClass>>() {}).toInstance(SubClass.class);
                requestInjection(holder);
            }
        });
        assertEquals(SubClass.class, holder.type);
    }

    @Test public void multibinderShouldBindSetOfClassesWithWildcard() {
        final SetHolder holder = new SetHolder();
        Guice.createInjector(new AbstractModule() {
            @Override protected void configure() {
                Multibinder.newSetBinder(binder(), new TypeLiteral<Class<? extends SuperClass>>() {}).addBinding().toInstance(SubClass.class);
                requestInjection(holder);
            }
        });
        assertEquals(singleton(SubClass.class), holder.types);
    }

    static class SuperClass {}

    static class SubClass extends SuperClass {}

    static class ClassHolder {
        @Inject Class<? extends SuperClass> type;
    }

    static class SetHolder {
        @Inject Set<Class<? extends SuperClass>> types;
    }
}

Binding generics with wildcard in Guice

1 Answers1