When should EntityManagerFactory instance be created/opened?

As per documentation : EntityManagerFactory instances are heavyweight objects. Each factory might maintain a metadata cache, object state cache, EntityManager pool, connection pool, and more. If your application no longer needs an EntityManagerFactory, you should close it to free these resources.

When an EntityManagerFactory closes, all EntityManagers from that factory, and by extension all entities managed by those EntityManagers, become invalid. It is much better to keep a factory open for a long period of time than to repeatedly create and close new factories. Thus, most applications will never close the factory, or only close it when the application is exiting.

Only applications that require multiple factories with different configurations have an obvious reason to create and close multiple EntityManagerFactory instances. Only one EntityManagerFactory is permitted to be created for each deployed persistence unit configuration. Any number of EntityManager instances may be created from a given factory.

More than one entity manager factory instance may be available simultaneously in the JVM. Methods of the EntityManagerFactory interface are threadsafe.

Thx for the tip! – masato-san Dec 28 '10 at 8:42.

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