Redefined - "Redefining the Service Layer with Groovy Categories"

Service.groovy

class LocalPaymentService implements PaymentService {
  	static {
		use (PaymentTypeHandlerRegistrationCategory) {
			CreditCardPaymentType.register(CreditCardPaymentProcessor)
			GiftCardPaymentType.register(GiftCardPaymentProcessor)
			EmployeePaymentType.register(EmployeePaymentProcessor)
			CheckPaymentType.register(CheckPaymentProcessor)
		}
	}

	public String process(PaymentType paymentType) {
		def processorCategory
		use (PaymentTypeHandlerRegistrationCategory) {
			processorCategory = paymentType.class.getHandler()
		}

		// No processor for the payment type
		if (!processorCategory) throw new RuntimeException("No handler registered for ${paymentType.class}")

		use (processorCategory) {
			paymentType.process()
		}
	}
}