Encapsulating the business logic with a POJO façade - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 261

An application can use local transactions if it only updates a single database via
JDBC , JDO , or Hibernate. However, applications that update multiple databases or
update a database and use JMS must use JTA .

Using JTA transactions
A JTA (or global) transaction is a transaction that involves multiple databases
and/or resources such as a JMS . An application uses JTA transaction either by
using the JTA API s directly or by using EJB container-managed transactions that
call the JTA API s internally. The JTA API s call the transaction manager (not to be
confused with the Spring PlatformTransactionManager interface), which is typi-
cally provided by the application server. The transaction manager coordinates the
atomic commit and rollback of the multiple resources.
To use a JTA transaction in a Spring application, you simply configure the
TransactionInterceptor with a JtaTransactionManager , which is a PlatformTrans-
actionManager that manages the transaction using the JTA API s. However, one
important difference between the JtaTransactionManager and the PlatformTrans-
actionManager s that manage local transactions is that it does not manage a persis-
tence framework connection. You can either let the ORM template class open the
connection, or you can use a persistence framework-specific interceptor. For exam-
ple, a HibernateInterceptor binds a Hibernate Session to the thread and a Jdo-
Interceptor binds a JDO PersistenceManager to the thread.

7.2.5 Implementing security

In the film The Lord of the Rings , the town of Bree has a gatekeeper who decides
who can enter the town. At night, when the gate is closed he looks through a
peephole to make sure that the visitor is not an enemy of the town. A façade that
encapsulates the business logic often plays the role of gatekeeper. It verifies that
the caller has permission to invoke a particular façade method. Hopefully, the
façades in your application will fare better than Bree's gatekeeper. Shortly after he
let in Frodo and his companions, the Black Riders sent the town's gate crashing
down on top of him.
An EJB can use the declarative security mechanism provided by the EJB con-
tainer, which verifies that the user has permission to execute a business method. It
also can call the EJBContext to get the identity of the caller and determine
whether the caller is in a particular role. A POJO façade does not use the EJB con-
tainer and so must adopt a different approach to security. It can either rely on the
presentation tier to provide security or, if the POJO façade must enforce security, it
can use a framework such as Acegi Security.