Theoretically, it should be written in service, because the dao layer is only for data persistence. Sometimes the business involves inserting data and uploading it, or deleting data and deleting files at the same time. This kind of business is usually implemented in service. Therefore, it is recommended that you put the service layer and do not use transactions if you want to check data

Write on the specific implementation method of dao.

Annotate on the business layer that the controller is a singleton by default. Under normal circumstances, just use the default thing