hibernate访问数据库代码与业务逻辑混杂在一起带来了很多问题，这样的程序设计严重影响了程序的可扩展性和适应性，所以数据库操作的代码分离出来与业务逻辑分离，形成“持久化层”的概念-hibernate to access the database code and business logic mixed together to bring a lot of problems, such a serious impact on program design process scalability and adaptability, so separate code for database operations and business logic, and form a " persistence layer"　The concept of