The EntityManager API is great, but how does the server/ application know which database it is supposed to save / update / query the entity objects?
How do we configure the underlying object-relational-mapping engine and cache for better performance and trouble shooting? The persistence.xml file gives you complete flexibility to configure the EntityManager.
- The persistence.xml file is a standard configuration file in JPA.
- It has to be included in the META-INF directory inside the JAR file that contains the entity beans.
- The persistence.xml file must define a persistence-unit with a unique name in the current scoped classloader.
- The provider attribute specifies the underlying implementation of the JPA EntityManager.
- In JBoss AS, the default and only supported / recommended JPA provider is Hibernate.
- The jta-data-source points to the JNDI name of the database this persistence unit maps to e.g. java:/DefaultDS.
