java8 Stream分组求和reducing&分组求最大值

最新推荐文章于 2025-04-12 17:48:37 发布

Java_LXM

最新推荐文章于 2025-04-12 17:48:37 发布

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文章标签： java 开发语言

本文链接：https://blog.youkuaiyun.com/Java_LXM/article/details/127873822

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1.将结果先分组，然后进行计算求和

// 将结果先分组，然后进行计算求和
List<Model> resultList = new ArrayList<>();
resultList = list.stream()
        .collect(Collectors.groupingBy(a -> a.get("goupBycode"))).values().stream()
        .map(b -> {
            Model model = new Model();
            Model.setMaterialcode(b.get(0).get("goupBycode").toString());
            Model.setStr1(b.stream()
                    .map(c -> new BigDecimal(c.get("str1") == null ? "0"
                        : c.get("str1").toString()))
                    .reduce(BigDecimal.ZERO, BigDecimal::add).toString());
            Model.setStr2(b.stream()
                    .map(c -> new BigDecimal(c.get("str2") == null ? "0"
                        : c.get("str2").toString()))
                    .reduce(BigDecimal.ZERO, BigDecimal::add).toString());
            return model;
        })
        .collect(Collectors.toList());

2.将结果先分组，返回某个数量的最大值

// 将结果先分组，返回某个数量的最大值
List<Model> resultList = new ArrayList<>();
Map<String, Model> stockCollects = list.stream()
    .collect(Collectors.groupingBy(Model::getGoupBycode, Collectors.collectingAndThen(Collectors.reducing(
            (c1, c2) -> Long.valueOf(c1.getStr()) > Long.valueOf(c2.getStr()) ? c1 : c2),
        Optional::get)));
if (stockCollects.size() > 0) {
    resultList = new ArrayList(stockCollects.values());
}