Guice - Dynamically selecting provider based on external parameter - groovy

Question

In guice, Is there a way to select particular implementation for binding based on some external parameter
Eg:
public interface Service {
void sendMessage()
}
class EmailService implements Service {
public EmailService() { }
#Override
void sendMessage() {
println "Sending email..."
}
}
class SMSService implements Service {
public EmailService() { }
#Override
void sendMessage() {
println "Sending sms..."
}
}
class Client {
private Service service
#Inject
Client(Service service) {
this.service = service
}
public void send() {
service.sendMessage()
}
}
public class ServiceProvider implements Provider<Service> {
Service get() {
return new SMSService() //Select implementation here?
}
}
public class MyModule extends AbstractModule {
#Override
protected void configure() {
bind(Service.class).toProvider(ServiceProvider.class).in(Scopes.SINGLETON)
}
}
public static void main(String...args) {
Injector injector = Guice.createInjector(new MyModule())
Client c = injector.getInstance(Client.class)
c.send()
}
In the above example, I'm forced to select which provider to use in Provider get() method. If I want to make this more dynamic, say for example, based on user preference, is there a way to wait select the provider at runtime and have guice inject it?

Answer 1

For these kind of problems, guice offers the MapBinder:
public class SnacksModule extends AbstractModule {
protected void configure() {
MapBinder<String, Snack> mapbinder
= MapBinder.newMapBinder(binder(), String.class, Snack.class);
mapbinder.addBinding("twix").toInstance(new Twix());
mapbinder.addBinding("snickers").toProvider(SnickersProvider.class);
mapbinder.addBinding("skittles").to(Skittles.class);
}
}
With this binding, a Map can now be injected:
class SnackMachine {
#Inject
public SnackMachine(Map<String, Snack> snacks) { ... }
}
You can define all your services in advance, and than pick the concrete instance (or provider) from the map byconfigured value.