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Declarative transaction management in Enterprise JavaBeans
Figure 19.2
Example of 2PC usage
Example 2PC usage with MDBs
At some point in time, an asynchronous message is delivered to OrderCompletionMDB by
invoking its onMessage() method, which has a REQUIRED transaction attribute. The
container starts a transaction using ITS and then invokes the onMessage() method. In
the body of the method, the bean updates the database to indicate order delivery. It is
important to note that there are 2 resources involved. The first one is the JMS
resource, which is associated with the MDB instances that got the message, and the
second is the database that the MDB instance updated. This scenario is similar to the
example diagram above.
Note ejb.transactionManagerInstanceName is also supported for MDBs. See Chapter 20,
“Message-Driven Beans and JMS” for more information.
Declarative transaction management in Enterprise JavaBeans
Transaction management for Enterprise JavaBeans (EJBs) is handled by the EJB
Container and the EJBs. Enterprise JavaBeans make it possible for applications to
update data in multiple databases within a single transaction.
EJBs utilize a declarative style of transaction management that differs from the
traditional transaction management style. With declarative management, the EJB
declares its transaction attributes at deployment time. The transaction attributes
indicate whether the EJB container manages the bean's transactions or whether the
bean itself manages its own transactions, and, if so, to what extent it does its own
transaction management.
Traditionally, the application was responsible for managing all aspects of a transaction.
This entailed such operations as:
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Creating the transaction object.
Explicitly starting the transaction.
Registering resources involved in the transaction.
Keeping track of the transaction context.
Committing the transaction when all updates completed.
It requires a developer with extensive transaction processing expertise to write an
application that is responsible for managing a transaction from start to finish. The code
for such an application is more complex and difficult to write, and it is easy for “pilot
error” to occur.
174 BES Developer’s Guide