将列表数据快速转换为树结构

/**
     * 构建树
     *
     * @param list
     * @return
     */
    private List<Map<String, Object>> buildTree(List<Map<String, Object>> list) {
        if (CollectionUtils.isEmpty(list)) {
            return new ArrayList<>();
        }
        for (Map<String, Object> item : list) {
            item.put("childs", new ArrayList<Map<String, Object>>());
        }
        Map<String, Map<String, Object>> kvMap = list2map(list);
        Iterator<Map<String, Object>> iterator = list.iterator();
        while (iterator.hasNext()) {
            Map<String, Object> item = iterator.next();
            String pid = (String) item.get("pid");
            if (StringUtils.isNotBlank(pid)) {
                Map<String, Object> pMap = kvMap.get(pid);
                if (pMap != null) {
                    List<Map<String, Object>> childs = (List<Map<String, Object>>) pMap.get("childs");
                    childs.add(item);
                    iterator.remove();
                }

            }
        }
        return list;
    }
    /**
     * list 转map
     *
     * @param list
     * @return
     */
    private Map<String, Map<String, Object>> list2map(List<Map<String, Object>> list) {
        Map<String, Map<String, Object>> map = new HashMap<>();
        for (Map<String, Object> item : list) {
            String id = (String) item.get("cost_id");
            map.put(id, item);
        }
        return map;
    }