Java8排重

List<CfUserContactDO> userContacts = new ArrayList<>();
...
//(oldValue, newValue) -> oldValue)
Map<Long, CfUserContactDO> dataMap = userContacts.stream().collect(Collectors.toMap(user -> user.getId(),
                                                                                    user -> user,
                                                                                    (user1, user2) -> user1));