在java流中按日期聚合数据

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        // 准备数据集合
        List<String> data = Arrays.asList(
                "2022-01-01,10",
                "2022-01-01,15",
                "2022-01-02,20",
                "2022-01-02,25",
                "2022-01-03,30"
        );

        // 转换日期格式为LocalDate对象
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        List<DataEntry> entries = data.stream()
                .map(s -> {
                    String[] parts = s.split(",");
                    LocalDate date = LocalDate.parse(parts[0], formatter);
                    int value = Integer.parseInt(parts[1]);
                    return new DataEntry(date, value);
                })
                .collect(Collectors.toList());

        // 使用流进行按日期聚合
        Map<LocalDate, Integer> result = entries.stream()
                .collect(Collectors.groupingBy(DataEntry::getDate, Collectors.summingInt(DataEntry::getValue)));

        // 输出聚合结果
        result.forEach((date, sum) -> System.out.println(date + ": " + sum));
    }

    // 数据实体类
    static class DataEntry {
        private LocalDate date;
        private int value;

        public DataEntry(LocalDate date, int value) {
            this.date = date;
            this.value = value;
        }

        public LocalDate getDate() {
            return date;
        }

        public int getValue() {
            return value;
        }
    }
}