Obtaining an EntityManager
Now that you have packaged and deployed your persistence units,
you need to obtain access to an EntityManager so that you can persist, update,
remove, and query your entity beans within your databases. In Java SE,
entity managers are created using a javax.persistence.EntityManagerFactory. Although
you can use the factory interface in Java EE, the platform provides some
additional features that make it easier and less verbose to manage entity
manager instances.
EntityManagerFactory
EntityManagers may be created or obtained from an EntityManagerFactory. In a Java SE
application, you must use an EntityManagerFactory to create instances of an
EntityManager. Using
the factory isn’t a requirement in Java EE, and we recommend
that you don’t use it directly from application code.
package javax.persistence;
import java.util.Map;
import javax.persistence.metamodel.Metamodel;
import javax.persistence.criteria.CriteriaBuilder;
public interface EntityManagerFactory
{
public EntityManager createEntityManager();
public EntityManager createEntityManager(Map map);
public CriteriaBuilder getCriteriaBuilder();
public Metamodel getMetamodel();
public boolean isOpen();
public void close();
public Map<String, Object> getProperties();
public Cache getCache();
public PersistenceUnitUtil getPersistenceUnitUtil();
}The createEntityManager() methods return EntityManager instances that manage a distinct
extended persistence context. You can pass in a java.util.Map parameter to override ...