说明：  比如说ajax的一些支持，统一的exception处理之类的，就是到数据库里查找树的记录，然后一顿循环递归，最后得到满足格式的树json串
(For example, some support ajax, unified exception handling and the like, is to find the database record of the tree, and then meal recursive loop, and finally met a tree json string format)