Business logic is the logic of processing data. General background code is also divided into three layers of actions (controllers). Service DAO (the three layers here are not MVC), for example, I get the user name, but when I store it in the database, the user name field should be the string action or the controller layer is the first layer, which is generally used to accept data and verify whether the data format is correct, such as whether the user name is empty or not, and whether it is a safe string. The vice layer is usually used to implement business logic. User Name = User Name+New Date (); DAO layer is the interactive layer with the database, that is, the read-write database inserts the new user name obtained from the logical layer into the database.