The example below demonstrates the Persistence class in
action. You will typically execute code like this on application startup, then
cache the resulting factory for future use. This bootstrapping code is only
necessary in non-EE environments; in an EE environment
EntityManagerFactories are typically injected.
Example 6.2. Obtaining an EntityManagerFactory
// if your persistence.xml file does not contain all settings already, you
// can add vendor settings to a map
Properties props = new Properties();
...
// create the factory defined by the "openjpa" entity-manager entry
EntityManagerFactory emf = Persistence.createEntityManagerFactory("openjpa", props);