Encapsulating the business logic with a POJO façade - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 259

A value of PROPAGATION_REQUIRED indicates this method must be executed in a
transaction. The TransactionInterceptor will start a transaction if one is not
already in progress.
The -net.chrisrichardson.bankingExample.facade.MoneyTransferException
entry is an example of a Spring rollback rule and tells the TransactionInterceptor
to roll back the transaction if the MoneyTransferException is thrown. By default,
Spring behaves like EJB and only rolls back a transaction if an unchecked excep-
tion is thrown, but you can override this behavior by configuring rollback rules.
This example uses a rollback rule that tells the TransactionInterceptor to roll
back when a checked exception is thrown, but you can also write rollback rules that
commit transactions when unchecked exceptions are thrown. An important bene-
fit of rollback rules is that they enable the application to roll back a transaction
without calling a Spring API . This is yet another example of how Spring does not
intrude on your application's code.
The transaction attributes for the getBalance() method, which matches the
get* wildcard, are
PROPAGATION_SUPPORTS, readOnly
The PROPAGATION_SUPPORTS value indicates that this method can be executed in a
transaction but does not require one. The readOnly value indicates that this
method does not update the database, which allows some database systems, to
optimize the transaction.
In addition to specifying the transaction attributes of each method, you must
specify the PlatformTransactionManager used by the TransactionInterceptor .
The PlatformTransactionManager is a Strategy (as in the Strategy pattern) that is
used by the TransactionInterceptor to begin, commit, and roll back transac-
tions. Figure 7.2 shows some of the different implementations of PlatformTrans-
actionManager .
The PlatformTransactionManager interface specifies three methods: get-
Transaction() , which begins a transaction; commit() , which commits a transaction;
and rollback() , which roll backs a transaction. Which kind of Platform-
TransactionManager you use depends on whether you are using local transactions
or JTA transactions. All of the examples in this topic use local transactions but can
easily be enhanced to use JTA transactions by simply reconfiguring the Trans-
actionInterceptor .