CustomerService bean是个工具类，它实现了访问数据库以增加、更新、删除和查询用户信息的方法。
The CustomerService bean is a utility class that implements methods to access the database for adding, updating, removing, and retrieving customer information.
每次用户被加入或从一个网络组中删除时，就应该增加这个版本号。
The version should increment every time the user is added to or deleted from a network group.
管理码（母码）可以删除或者增加用户码（子码）；
Master password can be used to add or delete any sub password.
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