java 树状结构生成 Lambda表达式写法

public class TreeUtil {

public static List<DepartmentTreeReturnVm> toTree(List<DepartmentEntity> datas) {
    //得到父节点
    return datas.stream()
            .filter(m -> !StringUtils.hasLength(m.getParentId()))
            .map(m -> {
                //可以根据需求赋予参数
                DepartmentTreeReturnVm vo = new DepartmentTreeReturnVm(m.getId(), m.getName());
                vo.setChildren(buildSubNodes(m, datas));
                return vo;
            }).collect(Collectors.toList());
}

private static List<DepartmentTreeReturnVm> buildSubNodes(DepartmentEntity root, List<DepartmentEntity> list) {
    return list.stream()
            .filter(m -> root.getId().equals(m.getParentId()))
            .map(m -> {
                //可以根据需求赋予参数
                DepartmentTreeReturnVm vo = new DepartmentTreeReturnVm(m.getId(), m.getName());
                vo.setChildren(buildSubNodes(m, list));
                return vo;
            }).collect(Collectors.toList());
}

}