The Java EE 5 Tutorial

The TxControllerBean Session Bean

The TxControllerBean session bean handles bank transactions. In addition to its get methods, getTxsOfAccount and getDetails, the TxControllerBean bean has several methods that change the balances of the bank accounts:

These methods access an Account entity to verify the account type and to set the new balance. The withdraw and deposit methods are for standard accounts, whereas the makeCharge and makePayment methods are for accounts that include a line of credit. If the type method argument does not match the account, these methods throw an IllegalAccountTypeException. If a withdrawal were to result in a negative balance, the withdraw method throws an InsufficientFundsException. If a credit charge attempts to exceed the account’s credit line, the makeCharge method throws an InsufficientCreditException.

The transferFunds method also checks the account type and new balance; if necessary, it throws the same exceptions as the withdraw and makeCharge methods. The transferFunds method subtracts from the balance of one Account instance and adds the same amount to another instance. Both of these steps must complete to ensure data integrity. If either step fails, the entire operation is rolled back and the balances remain unchanged. The transferFunds method, like all methods in session beans that use container-managed transaction demarcation, has an implicit Required transaction attribute. That is, you don’t need to explicitly decorate the method with a @TransactionAttribute annotation.