java - Why does BindingResult have to follow @Valid?

Question

I was struggling to get my Spring MVC validation to return to the page submitted page when I had errors. I finally solved the problem by noticing that BindingResult needs to be next to form parameter I'm validating.

For example if I amend the checkPersonInfo method in the spring.io tutorial(http://spring.io/guides/gs/validating-form-input/) to -

@RequestMapping(value="/", method=RequestMethod.POST)
public String checkPersonInfo(@Valid Person person, BindingResult bindingResult, Model model) {
    if (bindingResult.hasErrors()) {
        return "form";
    }
    return "redirect:/results";
}

Then it will work and redirect to the form page, but if I change it to -

@RequestMapping(value="/", method=RequestMethod.POST)
public String checkPersonInfo(@Valid Person person, Model model, BindingResult bindingResult) {
    if (bindingResult.hasErrors()) {
        return "form";
    }
    return "redirect:/results";
}

Then it redirects to /errors

What is the cause of this?

Answer 1

The BindingResult has to follow the object that is bound. The reason is that if you have more objects that are bound you must know which BindingResult belongs to which object.