Guice: One “Provider” for multiple implementations

Question

I have an interface that has 20 or so annotated implementations. I can inject the correct one if I know which I need at compile time, but I now need to dynamically inject on

Answer 1

Inject a MapBinder.

In your module, load the bindings into the MapBinder, then make your runtime parameters injectable as well. This example is based on the one in the documentation:

public class SnacksModule extends AbstractModule {
  protected void configure() {
    MapBinder mapbinder
           = MapBinder.newMapBinder(binder(), String.class, Snack.class);
    mapbinder.addBinding("twix").to(Twix.class);
    mapbinder.addBinding("snickers").to(Snickers.class);
    mapbinder.addBinding("skittles").to(Skittles.class);
  }
}

Then, in your object, inject the Map and the parameter. For this example I will assume you've bound a java.util.Properties for your runtime parameters:

@Inject
public MyObject(Map> snackProviderMap, Properties properties) {
  String snackType = (String) properties.get("snackType");
  Provider = snackProviderMap.get(property);
  
  // etc.
}

Note, with the same MapBinder you can inject either a simple Map or a Map>; Guice binds both.