Hibernate sessions in multi-threading

Question

I am currently trying to learn about the hibernate sessions. So, I am trying to process run some processes using CompletableFuture in java. The function inside the supplyAsync() has some DB processes to run. Earlier, I was running into no session currently bound to execution context even when I added @UnitOfWork to my resource.

In order to solve the issue, now I am currently opening and closing the session within the DAO's method findAll(). Since, the codebase is very big, I am going to only add a file which can illustrate the concern.

Main.java

import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

public class Supply {

    public static void main(String... args) throws ExecutionException, InterruptedException {
      final CompletableFuture<Integer> future = CompletableFuture
          .supplyAsync(() -> doSomethingAndReturnA())
          .thenApply(a -> convertToB(a));

      System.out.println(future.get());
    }

    private static int convertToB(final String a) {
      System.out.println("convertToB: " + Thread.currentThread().getName());
      return Integer.parseInt(a);
    }

    private static String doSomethingAndReturnA() {
      System.out.println("doSomethingAndReturnA: " + Thread.currentThread().getName());
      try {
        // some DB processes
        List<String> list = someDAO.findAll(); // opening and closing session in findAll()
        Thread.sleep(1000);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }

      return "1";
    }
}

public List<String> findAll() throws Exception{
        List<String> temp = null;
        Session session = sessionFactory.openSession();
        LOGGER.debug("Opened the session");
        try {
            ManagedSessionContext.bind(session);
            Transaction transaction = session.beginTransaction();
                try {
                    temp = list((Query<String>) namedQuery("something.findAll"));
                    transaction.commit();
                }
                catch (Exception e) {
                    transaction.rollback();
                    throw new Exception(e.getMessage());
                }
        } finally {
            session.close();
            ManagedSessionContext.unbind(sessionFactory);
        }
        return temp;
    }

1. Since, I added @UnitOfWork in my resource file where I am calling my doSomethingAndReturnA() directly, do I need to worry about separate sessions which are going to be opened in findAll().

2. I also read that I can access getCurrentSession() which will only create a session if it doesn't exists but for that I need a hibernate.cfg.xml and add current_session_context_class. Is there a way to write that file?

Of the two methods getCurrentSession() vs opening and closing sessions, which is more efficient and scalable.