Quite often, you need to provide users with the same data, but in different forms, like JSON, PDF, XLS, etc. If your application is Spring Framework-based, this task can be achieved using HTTP message converters.
HTTP message converters are applied when an HTTP request (or its parts) needs to be converted into type required for handler method argument (for more info, see Handler methods — method arguments), or when the value is returned by handler method needs to be converted somehow to create HTTP response (for more info, see Handler methods — Return values).