What is the use of EntityManager?
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Also, what is an EntityManager?
Entity manager. The EntityManager is an API that manages the lifecycle of entity instances. An EntityManager object manages a set of entities that are defined by a persistence unit. Each EntityManager instance is associated with a persistence context.
Subsequently, question is, do I need to close EntityManager? The EntityManager. close method closes an entity manager to release its persistence context and other resources. After calling close, the application must not invoke any further methods on the EntityManager instance except for getTransaction and isOpen , or the IllegalStateException will be thrown.
Also to know is, what is the use of @PersistenceContext?
You can use the @PersistenceContext annotation to inject an EntityManager in an EJB 3.0 client (such as a stateful or stateless session bean, message-driven bean, or servlet). You can use @PersistenceContext without specifying a unitName attribute to use the OC4J default persistence unit, as Example 29-12 shows.
What is the difference between session and EntityManager?
Session is a hibernate-specific API, EntityManager is a standardized API for JPA. You can think of the EntityManager as an adapter class that wraps Session (you can even get the Session object from an EntityManager object via the getDelegate() function).