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List<User> lists = 从某处得来的集合;
lists = lists.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<(Comparator.comparing(User::getXxx))), ArrayList::new));

针对于多个字段的去重，我们可以进行拼接去重:

List<Map<String, String>> arrayList = list.stream().
collect(Collectors.collectingAndThen(Collectors.toCollection(
() -> new TreeSet<>(Comparator.comparing(o -> o.get(“name”) + “:” + o.get(“address”) + “:” + o.get(“sex”)))), ArrayList::new));

从list集合中抽取getId转为新的集合：

List<NatCustomers> natCustomersList = natCustomersService.queryListByPage(0,1000);
List<Integer> customerIds = natCustomersList.stream().map(NatCustomers::getId).collect(Collectors.toList());

把list集合按getCustomerId字段进行分组：

List<ConsumptionStatistics>  consumptionStatistics = natServicesService.getConsumptionStatistics(paramMap);
Map<Integer, List<ConsumptionStatistics>> collect = consumptionStatistics.stream().collect(Collectors.groupingBy(ConsumptionStatistics::getCustomerId));