TrxCodeFinal.java

@Transactional
public void updateAllFriends() {
    Batch<Collection<User>> usersBatch = loadAllUsersBatch();
    for (Collection<User> users : usersBatch) {
        for (User user : users) {
            Collection<User> friends = fetchFriends(user);
            TransactionUtils.requiresNewTransaction(() -> {
                User newUser = repo.findOne(user.getId())
                newUser.getFriends().addAll(friends);
                newUser.setLastUpdateTime(new Date());
            });
        }
    }
}