Reading data from a Database in a thread-safe manner

Question

In my app I have a "Manager" class that has a reference to a DAO class which loads data from DB and populate a HashMap as a cache solution.

Here is a snippet

class UserManager {
   private final UserDAO userDAO;

   private final Map<Long, User> users;
   private final StampedLock lock = new StampedLock();

   public UserManager() {
     loadUsersFromDB();
   }

   // 99% of the times this method is called
   public getUserById(long id) {
      long stamp = lock.readLock();
       try {
         return users.get(id);
       } finally {
         lock.unlock(stamp);
       }
   }
 
   // This is done once when CTOR calls it and from time to time
   // by explicitly calling it from outside.
   public void loadUsersFromDB() {
 
      Map<Long, User> loadedUsers = userDAO.loadUsers();       

      long stamp = lock.writeLock();
      try {
        this.users = loadedUsers;
        
      } finally {
        lock.unlock(stamp);
      }
   }
}

This code work in a multithreaded environment, and the concern here is the use of StampedLock in this situation is an OVERKILL since most of the time it does READ operations and once in a while a simple load from DB and assignment to a class member.

I'm thinking to remove the StampedLock and instead use a simple AtomicReference<Map<Long, User>>, this way most of the time it's going to be a simple get and once in a while a set.

What do you think??