Java and Transaction processing

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A typical enterprise application accesses and stores information in one or more databases. This information must be accurate, current and reliable as it is critical for business operations. Data integrity would be lost if multiple programs were allowed to simultaneously update the same information. Also, it would be lost if a system that failed while processing a business transaction were to leave the affected data only partially updated. By preventing both of these scenarios, software transactions ensure data integrity. Transactions control the concurrent access of data by multiple programs. In the event of a system failure, transactions make sure that after recovery the data will be in a consistent state. Oracle9iAS provides a full support for transactions. There are two types of transactions:

• Container Managed Transactions
• Bean Managed Transactions

Container Managed Transactions

For an EJB with container-managed transactions, the container sets the boundaries of the transactions. Container-managed transactions can be used with any type of EJBs: session, entity or message-driven beans. Container-managed transactions simplify development because the EJB code does not explicitly mark the transaction's boundaries. The code does not include statements that begin and end the transaction.

Bean Managed Transactions

For an EJB with bean-managed transaction, the code in the session or message-driven bean explicitly marks the boundaries of the transaction. An entity bean may not have bean-managed transactions; it must use container-managed transactions instead. Although beans with container-managed transactions require less coding, they have one limitation: When a method is executing, it can be associated with either a single transaction or no transaction at all. If this limitation will make coding your bean difficult, you should consider using bean-managed transactions.

Demonstration

This sample (EJB Transaction Processing) assumes 2 different schemas for demonstrating transactions. The car information is contained in car_dealer table in a different database. A transaction is initiated before persisting the new reservation information in the hotel schema and the car booking information in a different schema. Only when both database operations succeed, the transaction is committed. The following figure shows the architecture of the EJB based implementation of the Hotel Reservation System.