Spring JpaRepository - Detach and Attach entity

entityManager.clear() will disconnect all the JPA objects, so that might not be an appropriate solution in all the cases, if you have other objects you do plan to keep connected.

clear

/**
 * Clear the persistence context, causing all managed
 * entities to become detached. Changes made to entities that
 * have not been flushed to the database will not be
 * persisted.
 */
public void clear();

entityManager.detach(entity); Remove the given entity from the persistence context

detach

/**
 * Remove the given entity from the persistence context, causing
 * a managed entity to become detached.  Unflushed changes made
 * to the entity if any (including removal of the entity),
 * will not be synchronized to the database.  Entities which
 * previously referenced the detached entity will continue to
 * reference it.
 * @param entity  entity instance
 * @throws IllegalArgumentException if the instance is not an
 *         entity
 * @since Java Persistence 2.0
 */
public void detach(Object entity);

If you are using JPA 2.0, you can use EntityManager#detach() to detach a single entity from persistence context. Also, Hibernate has a Session#evict() which serves the same purpose.

Since JpaRepository doesn't provide this functionality itself, you can add a custom implementation to it, something like this

public interface UserRepositoryCustom {
    ...
   void detachUser(User u);
    ...
}

public interface UserRepository extends JpaRepository<User, Long>, UserRepositoryCustom {
    ...
}

@Repository
public class UserRepositoryCustomImpl implements UserRepositoryCustom {
    ...
    @PersistenceContext
    private EntityManager entityManager;

    @Override
    public void detachUser(User u) {
        entityManager.detach(u);
    }
    ...
}

I haven't tried this code, but you should be able to make it work. You might even try to get a hold on EntityManager in your service class (where updateUser() is) with @PersistenceContext, and avoid the hustle of adding custom implementation to repository.