public static List getTreeList(String topId, List entityList) {
//存储顶层的数据
List resultList = new ArrayList<>();
Map<Object, OperatingStatementDto> treeMap = new HashMap<>(16);

    for (int i = 0; i < entityList.size() && !entityList.isEmpty(); i++) {
        OperatingStatementDto itemTree = entityList.get(i);
        //把所有的数据放到map当中，pid为key
        treeMap.put(itemTree.getNid(), itemTree);
        //把顶层数据放到集合中
        if (topId.equals(Integer.toString(itemTree.getPid())) || itemTree.getPid() == null) {
            resultList.add(itemTree);
        }
    }
    // 循环数据，把数据放到上一级的childen属性中
    for (int i = 0; i < entityList.size() && !entityList.isEmpty(); i++) {
        OperatingStatementDto itemTree = entityList.get(i);  // 在map集合中寻找父亲
        OperatingStatementDto data = treeMap.get(itemTree.getPid());
        // 判断父亲有没有
        if (data != null) {
            if (data.getChildren() == null) {
                data.setChildren(new ArrayList<>());
            }
            // 把子节点 放到父节点childList当中
            data.getChildren().add(itemTree);
            // 把放好的数据放回map当中
            treeMap.put(itemTree.getPid(), data);
        }
    }
    return resultList;
}