public static <T> PRedicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {    Map<Object, Boolean> seen = new ConcurrentHashMap<>();    return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;}
deviceRecords.stream().filter(distinctByKey(deviceRecord -> deviceRecord.getDeviceMac())).forEach(deviceRecord -> {    System.out.println(deviceRecord.getDeviceMac());});