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Integration with Java EE services
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The Java Transaction API (JTA) is the standardized service interface for transaction control in Java enterprise applications. It exposes several interfaces, such as the UserTransaction API for transaction demarcation and the TransactionManager API for participation in the transaction lifecycle. The transaction manager can coordinate a transaction that spans several resources imagine working in two Hibernate Sessions on two databases in a single transaction. A JTA transaction service is provided by all Java EE application servers. However, many Java EE services are usable stand-alone, and you can deploy a JTA provider along with your application, such as JBoss Transactions or ObjectWeb JOTM. We won t have much to say about this part of your configuration but focus on the integration of Hibernate with a JTA service, which is the same in full application servers or with stand-alone JTA providers. Look at figure 2.6. You use the Hibernate Session interface to access your database(s), and it s Hibernate s responsibility to integrate with the Java EE services of the managed environment.
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In such a managed environment, Hibernate no longer creates and maintains a JDBC connection pool Hibernate obtains database connections by looking up a Datasource object in the JNDI registry. Hence, your Hibernate configuration needs a reference to the JNDI name where managed connections can be obtained.
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<hibernate-configuration> <session-factory> <property name="hibernate.connection.datasource"> java:/MyDatasource
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</property> <property name="hibernate.dialect"> org.hibernate.dialect.HSQLDialect </property> ... </session-factory> </hibernate-configuration>
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With this configuration file, Hibernate looks up database connections in JNDI using the name java:/MyDatasource. When you configure your application server and deploy your application, or when you configure your stand-alone JTA provider, this is the name to which you should bind the managed datasource. Note that a dialect setting is still required for Hibernate to produce the correct SQL.
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Hibernate with Tomcat Tomcat isn t a Java EE application server; it s just a servlet container, albeit a servlet container with some features usually found only in application servers. One of these features may be used with Hibernate: the Tomcat connection pool. Tomcat uses the DBCP connection pool internally but exposes it as a JNDI datasource, just like a real application server. To configure the Tomcat datasource, you need to edit server.xml, according to instructions in the Tomcat JNDI/JDBC documentation. Hibernate can be configured to use this datasource by setting hibernate.connection.datasource. Keep in mind that Tomcat doesn t ship with a transaction manager, so you still have plain JDBC transaction semantics, which Hibernate can hide with its optional Transaction API. Alternatively, you can deploy a JTA-compatible standalone transaction manager along with your web application, which you should consider to get the standardized UserTransaction API. On the other hand, a regular application server (especially if it s modular like JBoss AS) may be easier to configure than Tomcat plus DBCP plus JTA, and it provides better services.
To fully integrate Hibernate with JTA, you need to tell Hibernate a bit more about your transaction manager. Hibernate has to hook into the transaction lifecycle, for example, to manage its caches. First, you need to tell Hibernate what transaction manager you re using:
<hibernate-configuration> <session-factory> <property name="hibernate.connection.datasource"> java:/MyDatasource </property>
Integration with Java EE services
<property name="hibernate.dialect"> org.hibernate.dialect.HSQLDialect </property> <property name="hibernate.transaction.manager_lookup_class"> org.hibernate.transaction.JBossTransactionManagerLookup </property> <property name="hibernate.transaction.factory_class"> org.hibernate.transaction.JTATransactionFactory </property> ... </session-factory> </hibernate-configuration>
You need to pick the appropriate lookup class for your application server, as you did in the preceding code Hibernate comes bundled with classes for the most popular JTA providers and application servers. Finally, you tell Hibernate that you want to use the JTA transaction interfaces in the application to set transaction boundaries. The JTATransactionFactory does several things:
It enables correct Session scoping and propagation for JTA if you decide to use the SessionFactory.getCurrentSession() method instead of opening and closing every Session manually. We discuss this feature in more detail in chapter 11, section 11.1, Propagating the Hibernate session. It tells Hibernate that you re planning to call the JTA UserTransaction interface in your application to start, commit, or roll back system transactions. It also switches the Hibernate Transaction API to JTA, in case you don t want to work with the standardized UserTransaction. If you now begin a transaction with the Hibernate API, it checks whether an ongoing JTA transaction is in progress and, if possible, joins this transaction. If no JTA transaction is in progress, a new transaction is started. If you commit or roll back with the Hibernate API, it either ignores the call (if Hibernate joined an existing transaction) or sets the system transaction to commit or roll back. We don t recommend using the Hibernate Transaction API if you deploy in an environment that supports JTA. However, this setting keeps existing code portable between managed and nonmanaged environments, albeit with possibly different transactional behavior.
There are other built-in TransactionFactory options, and you can write your own by implementing this interface. The JDBCTransactionFactory is the default in a nonmanaged environment, and you have used it throughout this chapter in
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