Using offline locking patterns - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 502

Because the business logic in this use case is simple, there isn't a separate POJO
façade and the AcknowledgeOrderService is called by directly by the presentation
tier. A Spring TransactionInterceptor ensures that each call to AcknowledgeOr-
derService executes within its own transaction. The same design works with both
Hibernate and JDO detached objects because the different API s for detaching and
attach objects are encapsulated behind the OrderAttachmentManager inter-
face.The responsibilities of each class are as follows:
■ AcknowledgeOrderService defines the public interface that encapsulates the
business logic.
■ AcknowledgeOrderServiceImpl implements the business logic.
■ Order is the domain object.
■ OrderRepository is used by the AcknowledgeOrderService to find the order.
■ OrderAttachmentManager encapsulates the mechanism for attaching and
detaching orders.
■ AcknowledgeOrderResult is returned by the service and contains a status
code and a detached order.

In this design, the presentation tier calls AcknowledgeOrderService.getOrder-
ToAcknowledge() , which returns the detached order, including its line items and
restaurants. The presentation tier displays the order to the user and stores it in
the HttpSession . When the user saves their changes, the presentation tier updates
the order by calling Order.accept() or Order.reject() , and then passes it to
AcknowledgeOrderService.acknowledgeOrder() . This method reattaches the
order, which updates the database with the changes. If the order has changed in
the database, the persistence framework throws an exception.

13.4.1 Implementing the domain service

Most of the business logic for this use case is implemented by AcknowledgeOrder-
ServiceImpl , which is shown in listing 13.1. It defines a getOrderToAcknowledge()
method, which returns the detached order, and an acknowledgeOrder() method,
which reattaches the updated order. AcknowledgeOrderServiceImpl uses an
OrderRepository to retrieve the order and an OrderAttachmentManager to detach
and attach the Order .

Listing 13.1 AcknowledgeOrderServiceImpl

public class AcknowledgeOrderServiceImpl implements
AcknowledgeOrderService {