spring boot 2. #Bean method invoked before injecting #Autowired dependency - spring

Question

This is just curiosity.
In example below #Autowired EntityManagerFactory and #Autowired ApplicationContext are injected before #Bean entityManager() method.
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
#Configuration
public class Config {
#Autowired
private EntityManagerFactory entityManagerFactory;
#Autowired
private ApplicationContext context;
#Bean
public EntityManager entityManager() {
EntityManager entityManager = entityManagerFactory.createEntityManager();
return entityManager;
}
}
But when i change EntityManager bean type to SessionFactory then sessionFactory() method is invoked before autowiring EntityManagerFactory and ApplicationContext beans causing NullPointerException when unwrapping SessionFactory. Code snippet below
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
#Configuration
public class Config {
#Autowired
private EntityManagerFactory entityManagerFactory;
#Autowired
private ApplicationContext context;
#Bean
public SessionFactory sessionFactory() {
EntityManager entityManager = entityManagerFactory.createEntityManager();
return entityManager.unwrap(SessionFactory.class);
}
}
And my question is: Why is this happening?

Answer 1

As of Hibernate 5.2 the SessionFactory is also an EntityManagerFactory as it now extends said interface. Prior to this the SessionFactory was wrapping an EntityManagerFactory.
Due to this the EntityManagerFactory cannot be injected because the SessionFactory is the actual bean implementing that interface.

Answer 2

As far as i remember there are two ways to obtain the SessionFactory:
From EntityManagerFactory
return entityManagerFactory.unwrap(SessionFactory.class)
//or -> if you have entitymanager
return em.getEntityManagerFactory().unwrap(SessionFactory.class);
From Session
Session session = entityManager.unwrap(Session.class);
return session.getSessionFactory();
And the reasons you are curious like as you said
sessionFactory() method is invoked before autowiring EntityManagerFactory and ApplicationContext beans causing NullPointerException
This is not the case