persistence.xml defines one or more persistence units. The following is an example persistence.xml file.
<persistence> <persistence-unit name="OrderManagement"> <description>This unit manages orders and customers. It does not rely on any vendor-specific features and can therefore be deployed to any persistence provider. </description> <jta-data-source>jdbc/MyOrderDB</jta-data-source> <jar-file>MyOrderApp.jar</jar-file> <class>com.widgets.Order</class> <class>com.widgets.Customer</class> </persistence-unit> </persistence>
This file defines a persistence unit named OrderManagement, which uses a JTA-aware data source jdbc/MyOrderDB. The jar-file and class elements specify managed persistence classes: entity classes, embeddable classes, and mapped superclasses. The jar-file element specifies JAR files that are visible to the packaged persistence unit that contain managed persistence classes, while the class element explicitly names managed persistence classes.
The jta-data-source (for JTA-aware data sources) and non-jta-data-source (non-JTA-aware data sources) elements specify the global JNDI name of the data source to be used by the container.