效果：

表数据的样子 

代码：

java"> public Result secondaryList() {List<MachineryType> machineryTypes = machineryTypeMapper.selectList(new QueryWrapper<MachineryType>().orderByAsc("pid"));// 创建父子关系Map<Integer, MachineryType> machineryTypeMap = machineryTypes.stream().collect(Collectors.toMap(MachineryType::getId, c -> c));List<MachineryType> outList = machineryTypes.stream().filter(c -> c.getPid() == 0) // 过滤出父节点.peek(parent -> {List<MachineryType> children = machineryTypes.stream().filter(child -> child.getPid().equals(parent.getId())).collect(Collectors.toList());parent.setChildren(children); // 设置子节点}).collect(Collectors.toList());return Result.success(outList);}