Using an exposed domain model - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 300

model services that are called by the presentation tier. The interceptor begins a
transaction when a domain model service is invoked and commits the transaction
when it returns. The interceptor might also roll back a transaction if an exception
is thrown. Figure 8.6 shows how the various classes collaborate in a design that
uses this approach.
The sequence of events is as follows:

The web container invokes the connection filter. 1

The connection filter calls the persistence framework to open the connec-
tion.

2

The filter calls the servlet.

3

The servlet invokes the PlaceOrderService . 4

The TransactionInterceptor begins the transaction.

5

The PlaceOrderService is invoked and updates the PendingOrder . 6

The TransactionInterceptor commits the transaction.

7

The servlet forwards the request to the JSP page. 8

The JSP uses the domain objects such as the PendingOrder to generate the
response.

9

The filter calls the persistence framework to close the connection.

10

Persistence
Tier

Presentation Tier Business Tier

:W e b
Container
doFilter()

: Transaction
Interceptor

: P l a c e O r d e r
Service

: Connection
Filter

:Persistence
Framework

:JSP

:Servlet :PendingOrder

open()

service()

updateDeliveryInfo()

beginTxn ()

serviceMethod()

commitTxn()

<<forward>>

getDeliveryAddress()

close()

Figure 8.6 Managing transactions with an AOP interceptor around the domain model services