Question

can you get 2 singleton instances of the same underlying type?

this is obviously trivial in spring as it is based on named instances to which you attach a scope but I can’t see the equivalent in guice which is about binding types to implementation classes. Note that I don’t want to have to bind to the instance as the instances in question are injected with other dependencies by guice.

Answer 1

It’s easy in Guice too! Create two biding annotations, say @One and @Two and then

bind(MySingleton.class).annotatedWith(One.class).toInstance(new MySingleton());
bind(MySingleton.class).annotatedWith(Two.class).toInstance(new MySingleton());

and then

@Inject
public SomethingThatDependsOnSingletons(@One MySingleton s1,
    @Two MySingleton t2) { ... }