Controller
@RequestMapping(value = "edit/{id}", method=RequestMethod.GET)
public ModelAndView edit(@ModelAttribute MyData mydata,
@PathVariable int id, ModelAndView mav) {
mav.setViewName("edit");
mav.addObject("title","edit mydata.");
Optional<MyData> data = repository.findById((long)id);
mav.addObject("formModel", data.get());
return mav;
}
@RequestMapping(value = "edit", method=RequestMethod.POST)
@Transactional(readOnly=false)
public ModelAndView update(@ModelAttribute MyData mydata,
ModelAndView mav) {
repository.saveAndFlush(mydata);
return new ModelAndView("redirect:/");
}
IDの値があるので、saveAndFlushでupdateされる


うお、Javaでやるとビビるな。なんでだろ〜