Here's a quick recap:

ExcelUtil: Utility class for converting User data to Excel. UserService: Service class for handling User business logic. UserController: Controller class for defining REST endpoints. You'll need to ensure your project is correctly configured with:

Database connection details in application.properties. Dependencies for MySQL, Spring Web, Spring Data JPA, Apache POI, etc., in your pom.xml. With this setup, you can:

Hit the appropriate API endpoint to fetch data from the database, which can return an Excel file using ExcelUtil. Upload an Excel file through an API endpoint, parse it using Apache POI, and save the data to the database using UserService.