Enterprise Bean (EJB) programming tutorials

Enterprise Beans Tutorial

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Enterprise Beans Tutorial

24 commit and rollback methods of the Connection interface. To demarcate JTA transactions, you invoke
the begin, commit, and rollback methods of the UserTransaction interface. · In a session bean with bean-managed transactions, it is possible to mix JDBC and JTA transactions.
This practice is not recommended, however, because it could make your code difficult to debug and
maintain. · If you're unsure about how to set up transactions in an enterprise bean, here's a tip: In the deployment
descriptor specify container-managed transactions. Then, set the Required transaction attribute for the
entire bean. This approach will work most of the time. FIGURE ; Options in Specifying Transactions Transaction Timeouts · For container-managed transactions, you control the transaction timeout interval by setting the value of
the transaction.timeout property in the config/default.properties file. For example, you would set the
timeout value to 5 seconds as follows: transaction.timeout=5 With this setting, if the transaction has
not completed within 5 seconds, the EJB container manager rolls it back. · When J2EE is first installed, the timeout value is set to 0: transaction.timeout=0
If the value is 0, the transaction will not time out. · Only enterprise beans with container-managed transactions are affected by the transaction.timeout
property. For enterprise beans with bean-managed, JTA transactions, you invoke the
setTransactionTimeout method of the UserTransaction interface. Isolation Levels · Transactions not only ensure the full completion (or rollback) of the statements that they enclose, they
also isolate the data modified by the statements. · The isolation level describes the degree to which the data being updated is visible to other transactions. · If the transaction allows other programs to read uncommitted data, performance may improve because
the other programs don't have to wait until the transaction ends. But there's a tradeoff-- if the transaction
rolls back, another program might read the wrong data. · You cannot modify the isolation level of a entity beans with container-managed persistence. These
beans use the default isolation level of the DBMS, which is usually READ_COMMITTED. · For entity beans with bean-managed persistence and for all session beans, you can set the isolation level
programmatically with the API provided by the underlying DBMS. A DBMS, for example, might allow