Question

I have an UI component that will be used in several UI module in an application.

I would like to annotate the UI component that to be injected into several other classes in one UI module to be a singleton, but not a singleton across the whole application. So that for each UI module use the UI component, one and only one of the UI component instance is used.

I couldn’t find a straight solution for this from the Guice document. So i think maybe I can use annotation to distinguish those instance?
Say in Module A, I annotate all the injection of the UI component with Named("ModuleA"); and in Module B, with Named("ModulaB"). and in the configuration, i tried to use something like:

this.bind(UIComponentA.class)
    .annotatedWith(Names.named("ModulaA"))
    .to(UIComponentAImpl.class).in(Singleton.class);

this.bind(UIComponentA.class)
    .annotatedWith(Names.named("ModulaB"))
    .to(UIComponentAImpl.class).in(Singleton.class);

Because UICompoenetAImpl also need to be injected, so I couldn’t simply create the instance there. Totally not sure if this works.

And I’m wondering what’s the standard way to accomplish this?

Answer 1

One other option might be to use a child injector for each module.

This would allow you to bind a difference instance of UIComponentA in each module. Bind them in the child injector rather than the parent. You would then need to make sure that all of your module’s dependencies are built from the right child injector, probably by making sure the root of each module is loaded from the right place.