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Bean-managed transactions
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// Perform transacted tasks. userTransaction.commit();
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On a related but relevant note, you cannot use the EJBContext getRollbackOnly and setRollbackOnly methods in BMT, and the container will throw an IllegalStateException if accessed. Next, let s see how the obtained UserTransaction interface is actually used.
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6.3.3 Using UserTransaction
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You ve already seen the UserTransaction interface s most frequently used methods: begin, commit, and rollback. The UserTransaction interface has a few other useful methods we should take a look at as well. The definition of the entire interface looks like this:
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public interface UserTransaction { void begin() throws NotSupportedException, SystemException; void commit() throws RollbackException, HeuristicMixedException, HeuristicRollbackException, SecurityException, IllegalStateException, SystemException; void rollback() throws IllegalStateException, SecurityException, SystemException; void setRollbackOnly() throws IllegalStateException, SystemException; int getStatus() throws SystemException; void setTransactionTimeout(int seconds) throws SystemException; }
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The begin method creates a new low-level transaction behind the scenes and associates it with the current thread. You might be wondering what would happen if you called the begin method twice before calling rollback or commit. You might think this is possible if you want to create a nested transaction, a paradigm supported by some transactional systems. In reality, the second invocation of begin would throw a NotSupportedException since Java EE doesn t support nested transactions. The commit and rollback methods, on the other hand, remove the transaction attached to the current thread by using the begin method. While commit sends a success signal to the underlying transaction manager, rollback abandons the current transaction. The setRollbackOnly method on this interface might be slightly counterintuitive as well. After all, why bother marking a transaction as rolled back when you can roll it back yourself
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Transactions and security
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To understand why, consider the fact that we could call a CMT method from our BMT bean that contains a lengthy calculation and checks the transactional flag before proceeding (like our Power Seller credit validation example in section 6.2.4). Since our BMT transaction would be propagated to the CMT method, it might be programmatically simpler, especially in a long method, to mark the transaction rolled back using the setRollbackOnly method instead of writing an involved if-else block avoiding such conditions. The getStatus method is a more robust version of getRollbackOnly in the CMT world. Instead of returning a boolean, this method returns an integer-based status of the current transactions, indicating a more fine-tuned set of states a transaction could possibly be in. The javax.transaction.Status interface defines exactly what these states are, and we list them in table 6.3. The setTransactionTimeout method specifies the time, in seconds, in which a transaction must finish. The default transaction timeout value is set to different values for different application servers. For example, JBoss has a default
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Table 6.3 The possible values of the javax.transaction.Status interface. These are the status values returned by the UserTransaction.getStatus method. Status STATUS_ACTIVE STATUS_MARKED_ROLLBACK Description The associated transaction is in an active state. The associated transaction is marked for rollback, possibly due to invocation of the setRollbackOnly method. The associated transaction is in the prepared state because all resources have agreed to commit (refer to the two-phase commit discussion in section 6.1.4). The associated transaction has been committed. The associated transaction has been rolled back. The status for associated transaction is not known (very clever, don t you agree ). There is no associated transaction in the current thread. The associated transaction is preparing to be committed and awaiting response from subordinate resources (refer to the two-phase commit discussion in section 6.1.4). The transaction is in the process of committing. The transaction is in the process of rolling back.
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STATUS_PREPARED
STATUS_COMMITTED STATUS_ROLLEDBACK STATUS_UNKNOWN
STATUS_NO_TRANSACTION STATUS_PREPARING
STATUS_COMMITTING STATUS_ROLLING_BACK
Bean-managed transactions
transaction timeout value of 300 seconds whereas Oracle Application Server 10g has a default transaction timeout value of 30 seconds. You might want to use this method if you re using a very long-running transaction. Typically, it is better to simply set the application server-wide defaults using vendor-specific interfaces, however. At this point, you are probably wondering how to set a transaction timeout when using CMT instead. This is only supported by containers using either an attribute in the vendor-specific deployment descriptor or vendor-specific annotations. Comparing listings 6.1 and 6.3, you might ask if the additional complexity and verbosity associated with BMT is really worth it. Let s explore this issue in detail next.
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