One other option is to utilize two different radio buttons and use the th:field="isPresent" option to specify that return attribute is named "isPresent".
I'm not sure if your stuff is working, but I don't see that you've assigned an object to your form. You can include th:object="AttendanceJson" in your 'form' HTML element.
yeah, but ... what would PIE do? Especially concerning this tiny ad: