No session to write JSON lazy load - spring

Question

I'm just starting with spring and hibernate. I'm trying to create some basic service using DAO.
Here is one of it:
#SuppressWarnings("unchecked")
#Override
public Users findByUserId(int id) {
List<Users> users = new ArrayList<Users>();
if(getSessionFactory() != null) {
try {
session = getSessionFactory().getCurrentSession();
users = session
.createQuery("from Users where id=?")
.setParameter(0, id)
.list();
} catch (HibernateException e) {
LOGGER.error("HibernateException: " + e);
}
}
if (!users.isEmpty()) {
return users.get(0);
} else {
return null;
}
}
And I called this service from a controller:
#RestController
public class JSONController {
#Autowired
private UserDao userDao;
#RequestMapping(value = "/rest/userbyid/{id}",
method = RequestMethod.GET,
headers = "Accept=application/json")
public Users getUserById(#PathVariable("id") int id) {
return userDao.findByUserId(id);
}
}
I understand that the session had been closed when the process come to controller. I can solve this by using openSession() method.
I just want to know is there any better way to handle this? Better still using getCurrentSession() (or any).

Answer 1

It's not good to return Entity to be serialized in controller. Imagine serializer which invokes all methods and even lazy collections.
For User instance it calls let's say getProjects() lazy method, then for each Project returned it agains call getUser() and so on.
Good practice is to define Service layer and return DTO (Data Transfer Object) which contains only necessary fields.
There is alternative approach to unproxy entities before return defining depth.
#SuppressWarnings("unchecked")
protected T unproxy(T entity){
if (entity == null) {
return null;
}
if (entity instanceof HibernateProxy) {
try {
Hibernate.initialize(entity);
} catch (ObjectNotFoundException e) {
return null;
}
entity = (T) ((HibernateProxy) entity).getHibernateLazyInitializer().getImplementation();
}
return entity;
}
From
https://gist.github.com/maikelsperandio/6889130