java8中的Stream API实战

目录

根据以下两个list集合来演示Stream API

List<PayRecordBO> list1 = new ArrayList<>();
PayRecordBO payRecordBO1 = new PayRecordBO();
payRecordBO1.setChannelNo("1");
payRecordBO1.setAmount(new BigDecimal("0.11"));
payRecordBO1.setResponseCode("success");
list1.add(payRecordBO1);

PayRecordBO payRecordBO2 = new PayRecordBO();
payRecordBO2.setChannelNo("2");
payRecordBO2.setAmount(new BigDecimal("0.05"));
payRecordBO2.setResponseCode("success");
list1.add(payRecordBO2);

PayRecordBO payRecordBO3 = new PayRecordBO();
payRecordBO3.setChannelNo("3");
payRecordBO3.setAmount(new BigDecimal("0.81"));
payRecordBO3.setResponseCode("success");
list1.add(payRecordBO3);

PayRecordBO payRecordBO35 = new PayRecordBO();
payRecordBO35.setChannelNo("5");
payRecordBO35.setAmount(new BigDecimal("0.31"));
payRecordBO35.setResponseCode("success");
list1.add(payRecordBO35);

PayRecordBO payRecordBO66 = new PayRecordBO();
payRecordBO66.setChannelNo("8");
payRecordBO66.setAmount(new BigDecimal("0.31"));
payRecordBO66.setResponseCode("fail");
list1.add(payRecordBO66);

PayRecordBO payRecordBO9 = new PayRecordBO();
payRecordBO9.setChannelNo("9");
payRecordBO9.setAmount(new BigDecimal("0.92"));
//payRecordBO9.setResponseCode("fail");
list1.add(payRecordBO9);

PayRecordBO payRecordBO10 = new PayRecordBO();
payRecordBO10.setChannelNo("10");
payRecordBO10.setAmount(new BigDecimal("1.92"));
payRecordBO10.setResponseCode("fail");
list1.add(payRecordBO10);

// ==========================

List<PayRecordBO> list2 = new ArrayList<>();
PayRecordBO payRecordBO4 = new PayRecordBO();
payRecordBO4.setChannelNo("4");
payRecordBO4.setAmount(new BigDecimal("0.31"));
list2.add(payRecordBO4);

PayRecordBO payRecordBO5 = new PayRecordBO();
payRecordBO5.setChannelNo("3");
payRecordBO5.setAmount(new BigDecimal("0.31"));
list2.add(payRecordBO5);

PayRecordBO payRecordBO6 = new PayRecordBO();
payRecordBO6.setChannelNo("2");
payRecordBO6.setAmount(new BigDecimal("0.22"));
list2.add(payRecordBO6);

PayRecordBO payRecordBO8 = new PayRecordBO();
payRecordBO8.setChannelNo("8");
payRecordBO8.setAmount(new BigDecimal("0.31"));
list2.add(payRecordBO8);

PayRecordBO payRecordBO99 = new PayRecordBO();
payRecordBO99.setChannelNo("9");
payRecordBO99.setAmount(new BigDecimal("0.19"));
list2.add(payRecordBO99);

PayRecordBO payRecordBO12 = new PayRecordBO();
payRecordBO12.setChannelNo("10");
payRecordBO12.setAmount(new BigDecimal("5.92"));
list2.add(payRecordBO12);

1、以list1为基准，两个list集合中根据某个字段求交集

List<PayRecordBO> eqList = list1.parallelStream().filter(x ->
		list2.parallelStream().map(PayRecordBO::getChannelNo).collect(Collectors.toList()).contains(x.getChannelNo())
).collect(Collectors.toList());
log.info("相同数据：{}",eqList);

2、以list1为基准，两个list集合中根据某个字段求差集

List<PayRecordBO> collect = list1.parallelStream().filter(x -> !eqList.contains(x)).collect(Collectors.toList());
log.info("差集数据：{}",collect);

3、以list1为基准，两个list集合中根据某个字段求交集

List<PayRecordBO> eqList = list1.parallelStream().filter(x ->
		list2.parallelStream().anyMatch(r -> r.getChannelNo().equalsIgnoreCase(x.getChannelNo()))
).collect(Collectors.toList());
log.info("相同数据：{}", eqList);

4、以list1为基准，两个list集合中根据某个字段求差集

List<PayRecordBO> poolList = list1.parallelStream().filter(x ->
		list2.parallelStream().noneMatch(r -> r.getChannelNo().equalsIgnoreCase(x.getChannelNo()))
).collect(Collectors.toList());
log.info("差集数据：{}", poolList);

5、以list1为基准，两个list集合中根据某两个字段求交集

List<PayRecordBO> intersectList = list1.stream()
		.filter(pe -> findOver(pe.getChannelNo(), pe.getAmount(), list2) > -1).collect(Collectors.toList());
log.info("平台长款：{}", intersectList);

6、以list1为基准，两个list集合中根据某两个字段求交集

List<PayRecordBO> shortList = list1.stream()
		.filter(pe -> findShort(pe.getChannelNo(), pe.getAmount(), list2) > -1).collect(Collectors.toList());
log.info("平台短款：{}", shortList);

7、以list2为基准，两个list集合求交集、差集

List<PayRecordBO> poolBankList = list2.parallelStream().filter(x ->
		list1.parallelStream().noneMatch(r -> r.getChannelNo().equalsIgnoreCase(x.getChannelNo()))
).collect(Collectors.toList());
log.info("bank缓存池数据：{}", poolBankList);

List<PayRecordBO> bankFailList = list2.stream()
		.filter(pe -> findFail(pe.getChannelNo(), pe.getAmount(), list1) > -1).collect(Collectors.toList());
log.info("bank状态不符数据，金额相同：{}", bankFailList);

List<PayRecordBO> bankFailOverList = list2.stream()
		.filter(pe -> findFailOver(pe.getChannelNo(), pe.getAmount(), list1) > -1).collect(Collectors.toList());
log.info("bank平台长款数据，状态不符：{}", bankFailOverList);

List<PayRecordBO> bankFailShortList = list2.stream()
		.filter(pe -> findFailShort(pe.getChannelNo(), pe.getAmount(), list1) > -1).collect(Collectors.toList());
log.info("bank平台短款数据，状态不符：{}", bankFailShortList);

8、求总金额

List<PayRecordBO> recRecord = list1.stream().filter(x -> RecConstant.IN.equalsIgnoreCase(x.getTransType())).collect(Collectors.toList());
List<PayRecordBO> recRefundRecord = list1.stream().filter(x -> RecConstant.OUT.equalsIgnoreCase(x.getTransType())).collect(Collectors.toList());
recRecord.stream().filter(x -> x.getAmount() != null).map(PayRecordBO::getAmount).reduce(BigDecimal.ZERO, BigDecimal::add);
recRefundRecord.stream().filter(x -> x.getAmount() != null).map(PayRecordBO::getAmount).reduce(BigDecimal.ZERO, BigDecimal::add);

9、CollectUtil工具类

public final class CollectUtil {

    public static int findFailShort(String playerId, BigDecimal amt, List<PayRecordBO> list) {
        int res = -1;
        for (int i = 0; i < list.size(); i++) {
            boolean flag = list.get(i).getChannelNo().equals(playerId)
                    && (StringUtils.isBlank(list.get(i).getResponseCode())
                    || !RecConstant.SUCCESS.equals(list.get(i).getResponseCode()))
                    && amt.compareTo(list.get(i).getAmount()) > 0;
            if (flag) {
                res = i;
                break;
            }
        }
        return res;
    }

    public static int findFailOver(String playerId, BigDecimal amt, List<PayRecordBO> list) {
        int res = -1;
        for (int i = 0; i < list.size(); i++) {
            boolean flag = list.get(i).getChannelNo().equals(playerId)
                    && (StringUtils.isBlank(list.get(i).getResponseCode())
                    || !RecConstant.SUCCESS.equals(list.get(i).getResponseCode()))
                    && amt.compareTo(list.get(i).getAmount()) < 0;
            if (flag) {
                res = i;
                break;
            }
        }
        return res;
    }

    public static int findFail(String playerId, BigDecimal amt, List<PayRecordBO> list) {
        int res = -1;
        for (int i = 0; i < list.size(); i++) {
            boolean flag = list.get(i).getChannelNo().equals(playerId)
                    && (StringUtils.isBlank(list.get(i).getResponseCode())
                    || !RecConstant.SUCCESS.equals(list.get(i).getResponseCode()))
                    && amt.compareTo(list.get(i).getAmount()) == 0;
            if (flag) {
                res = i;
                break;
            }
        }
        return res;
    }


    public static int findShort(String playerId, BigDecimal amt, List<PayRecordBO> list) {
        int res = -1;
        for (int i = 0; i < list.size(); i++) {
            if (list.get(i).getChannelNo().equals(playerId) && amt.compareTo(list.get(i).getAmount()) < 0) {
                res = i;
                break;
            }
        }
        return res;
    }


    public static int findOver(String playerId, BigDecimal amt, List<PayRecordBO> list) {
        int res = -1;
        for (int i = 0; i < list.size(); i++) {
            if (list.get(i).getChannelNo().equals(playerId) && amt.compareTo(list.get(i).getAmount()) > 0) {
                res = i;
                break;
            }
        }
        return res;
    }

    public static <T> Predicate<T> distinctByKey(Function<? super T, Object> keyExtractor) {
        Map<Object, Boolean> seen = new ConcurrentHashMap<>();
        return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
    }

}
posted @ 2020-09-02 08:58  kevin_ying  阅读(372)  评论(0)  编辑  收藏  举报
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