Redefining - "Redefining the Service Layer with Groovy Categories"

Processor.groovy

class CreditCardPaymentProcessor {
        static {
            CreditCardPaymentProcessor.metaClass.static.methodMissing = { String name, args ->
                if (name.startsWith("getGatewayFor")) {
                    def state = name.replaceAll("getGatewayFor","")?.toLowerCase()
                    switch (state) {
                        case "ca":
                            return new CheckPaymentProcessor()
                        default:
                            return new CreditCardPaymentProcessor()
                    }
                }
            }
        }

  	static String process(PaymentType paymentType) {
		def gateway = "getGatewayFor${paymentType.payee.billingAddress.state}"()
		process gateway, paymentType
	}

	static String process(CheckPaymentGateway paymentGateway, PaymentType paymentType) {
		// ...
	}

	static String process(CreditCardPaymentGateway paymentGateway, PaymentType paymentType) {
		// …
	}
}