Java lamda表达式常用demo

public static String extractIdFromTags(List<String> tags) {
    if (CollectionUtils.isEmpty(tags)) return "";

    List<String> validYears = Arrays.asList("2023", "2024", "2025", "2026", "2027");

    String txid = tags.stream()
            .filter(x -> validYears.stream().anyMatch(year -> x.startsWith(year)))
            .filter(x -> x.length() > 20 && x.length() <= 32)
            .findFirst()
            .orElse("");

    return txid.toUpperCase();
}

判断字符串是否以指定的年份开头，并且长度大于20且小于等于32，可以对条件进行组合判断

BigDecimal sum = successNumVos.stream().map(x -> Optional.ofNullable(x.getSuccessAmount()).orElse(BigDecimal.ZERO)).reduce(BigDecimal.ZERO, BigDecimal::add);

List<MianshiLogical> list = new ArrayList<>();
// 假设你有一个包含MianshiLogical对象的列表list

// 使用Java Lambda根据logialCategory进行分组
Map<String, List<String>> groupedMap = list.stream()
        .collect(Collectors.groupingBy(MianshiLogical::getLogialCategory,
                Collectors.mapping(MianshiLogical::getLogialNum, Collectors.toList())));

 List<Integer> roleIdList = Arrays.asList(16, 17, 18, 22, 26);
            List<UserRole> filterList = list.stream()
                    .filter(x -> roleIdList.contains(x.getRoleId()))
                    .collect(Collectors.toList());

Map<String, List<AccountWeightVo>> weightMap = paymentAccount.stream()
        .collect(Collectors.groupingBy(MerchantAccountRecord::getMerchantId,
                Collectors.mapping(record -> new AccountWeightVo(record.getAccountId(), record.getWeight()), Collectors.toList())));