Service Provider Framework Sketch

// Service provider framework sketch

// Service interface
public interface Service {
    // Service-specific methods go here
}
 
// Service provider interface
public interface Provider {
    Service newService();
}
 
// Noninstantiable class for service registration and access
public class Services {
    private Services() { } // Prevents instantiation
    // Maps service names to services
    private static final Map<String, Provider> providers = new ConcurrentHashMap<String, Provider>();
    public static final String DEFAULT_PROVIDER_NAME = "<def>";
 
    // Provider registration API
    public static void registerDefaultProvider(Provider p) {
        registerProvider(DEFAULT_PROVIDER_NAME, p);
    }
    public static void registerProvider(String name, Provider p){
        providers.put(name, p);
    }
 
    // Service access API
    public static Service newInstance() {
        return newInstance(DEFAULT_PROVIDER_NAME);
    }
    public static Service newInstance(String name) {
        Provider p = providers.get(name);
        if (p == null)
            throw new IllegalArgumentException("No provider registered with name: " + name);
    return p.newService();
    }
}