java stream 递归 分组

可以使用Java Stream的递归分组来实现该功能。下面是一个示例代码：

import java.util.*;
import java.util.stream.*;

public class RecursiveGrouping {
    public static void main(String[] args) {
        List<Map<String, Object>> data = Arrays.asList(
            Map.of("id", 1, "name", "Alice", "parent_id", null),
            Map.of("id", 2, "name", "Bob", "parent_id", 1),
            Map.of("id", 3, "name", "Charlie", "parent_id", 2),
            Map.of("id", 4, "name", "Dave", "parent_id", 3),
            Map.of("id", 5, "name", "Eve", "parent_id", 2),
            Map.of("id", 6, "name", "Frank", "parent_id", null),
            Map.of("id", 7, "name", "Grace", "parent_id", 6),
            Map.of("id", 8, "name", "Hank", "parent_id", 7)
        );
        
        Map<String, List<Map<String, Object>>> result = groupByParentId(null, data);
        System.out.println(result);
    }
    
    private static Map<String, List<Map<String, Object>>> groupByParentId(Object parentId, List<Map<String, Object>> data) {
        return data.stream()
            .filter(map -> Objects.equals(map.get("parent_id"), parentId))
            .collect(Collectors.groupingBy(map -> map.get("name").toString(),
                Collectors.mapping(map -> groupByParentId(map.get("id"), data), Collectors.toList())));
    }
}

这个示例代码将给定的数据列表按照parent_id递归分组，并返回一个Map对象，其中键为每个组的名称，值为该组内的所有元素列表。这个方法可以递归地处理任意深度的嵌套分组。