Guice module with type parameters

Question

I spent some time wondering if it is possible to write a guice module which itself is parametrized with type T and uses its type parameter to specify bindings.

Like in this (not working) example:

interface A<T> {} 
class AImpl<T> implements A<T>{} 
interface B<T> {} 
class BImpl<T> implements B<T> {} 

class MyModule<T> extends AbstractModule { 
    @Override 
    protected void configure() { 
        bind(new TypeLiteral<A<T>>(){}).to(new TypeLiteral<AImpl<T>>(){});
        bind(new TypeLiteral<B<T>>(){}).to(new TypeLiteral<BImpl<T>>(){}); 
    } 
} 

I tried different approaches passing trying to pass T to MyModule as instance of Class/TypeLiteral but none of them worked. Help appreciated.

Regards, Łukasz Osipiuk

Answer 1

For that you will have to build each TypeLiteral from scratch, using com.google.inject.util.Types. You could do something like that:

class MyModule<T> extends AbstractModule {
    public MyModule(TypeLiteral<T> type) {
        _type = type;
    }

    @Override protected void configure() {
        TypeLiteral<A<T>> a = newGenericType(A.class);
        TypeLiteral<AImpl<T>> aimpl = newGenericType(AImpl.class);
        bind(a).to(aimpl);
        TypeLiteral<B<T>> b = newGenericType(B.class);
        TypeLiteral<BImpl<T>> bimpl = newGenericType(BImpl.class);
        bind(b).to(bimpl);
    }

    @SuppressWarnings("unchecked")
    private <V> TypeLiteral<V> newGenericType(Class<?> base) {
        Type newType = Types.newParameterizedType(base, _type.getType());
        return (TypeLiteral<V>) TypeLiteral.get(newType);
    }

    final private TypeLiteral<T> _type;
}

Please note that the private method newGenericType() will perform no control on types, it is your responsibility, in configure(), to make sure that generic types can be correctly built with that method.