Strict Service Locator

gistfile1.txt

public class ServiceLocator {

	//
	// instance fields
	//
	private final static Map<Class, Object> _Services;
	

	//
	// constructors
	//

	static {
		_Services = new HashMap<Class, Object>();
	}


	//
	// operations
	//
	
	public static void registerLocationService( LocationService locationService ){
		registerSingletonService( locationService );
	}
	public static LocationService resolveLocationService() {
		return resolveSingletonService( LocationService.class );
	}
	

	//
	// private methods
	//

	private static <TService> void registerSingletonService( TService service ){
		Preconditions.shouldNotBeNull( service, "service" );

		// ensure service is not already registered
		final Class<?> serviceClass = service.getClass();
		if( _Services.get( serviceClass ) != null )
			throw new IllegalStateException( String.format( "Service %s is already registered", service ));

		_Services.put( serviceClass, service );
	}


	private static <TService> TService resolveSingletonService( Class serviceClass ){
		Preconditions.shouldNotBeNull( serviceClass, "serviceClass" );

		// ensure service is registered
		if( !_Services.containsKey( serviceClass ))
			throw new IllegalStateException( String.format( "No %s service registered", serviceClass.getSimpleName() ));

		return (TService)_Services.get( serviceClass );
	}
	
}