String 转 List<Long>
String string = "1, 2, 3, 4";
List<Long> list = Arrays.asList(string.split(",")).stream().map(s -> Long.parseLong(s.trim())).collect(Collectors.toList());
List<Long> 转 String
String str = Arrays.toString(listIds.toArray()); //[1,2,3,3,4]