Spring form validation problems

I'm writing a web app with spring and I'm having problems with forms validation. It's the first time I use that, so I still have to understand it...

Basically I have a controller with the form handling method that is :

@RequestMapping(params = "action=gestprodotti")
    public ModelAndView doGestProdotti(
            @RequestParam(value = "page", required = false, defaultValue = "0") int page,
            @RequestParam(value = "activity", required = false) String activity,
            @ModelAttribute Prodotto prod, BindingResult bindresult,
            HttpSession session) throws Exception {

the controller is annotated and doesn't extend anything. Later in the method, after receiving the object bound to the form, I do:

Validator valid = activityHandler.getValidator();
            valid.validate(backingObject, bindresult);
            if (bi开发者_如何学Cndresult.hasErrors()){
                return handleRequest(action, ACTIVITY_NEW_ITEM, jspComponent,
                        page, itemId, backingObject, bindresult, appstatus);
            }

that means that I call manually the validator and give back the same form page (a ModelAndView result).

The validator code:

public static final class ProdottoValidator implements Validator{

        @Override
        public boolean supports(Class<?> other) {
            return Prodotto.class.isAssignableFrom(other);          
        }

        @Override
        public void validate(Object obj, Errors errors) {
            ValidationUtils.rejectIfEmptyOrWhitespace(errors, "codice", "Il codice è richiesto");           
        }

    }

and the relevant JSP code:

<td colspan="2" align="left">Codice<form:input id="code"
                path="codice" /><form:errors path="codice" /></td>

that works fine for binding, but I don't get any error. I didn't create any messages.properties file, but I think I should see something anyway. Errors are detected because bindresult.hasErrors() gives true, but the rendered html doesn't show up anything in place of form:errors. Am I missing something like configuration or whatever? Is it because there is not a messages.properties file that it doesn't work?

This is a typical symptom of model attribute name mismatch.

Model attribute name should be the same in three places:

1. In form setup method, where you put initial state of the form object into the model.

2. In <form:form> element of JSP page. Default name here is command, it can be configured using modelAttribute attribute (or commandName, it's the same thing).

3. In form processing method, such as your doGestProdotti. Default name is inferred as an argument class name with the first letter decapitalized (prodotto in your case). You can specify the name explicitly with @ModelAttribute("...").

Mismatch between points (2) and (3) causes validation errors not being displayed. Mismatch between points (1) and (2) causes binding errors when displaying a form.

So, you need either to configure prodotto as a model attribute name in points (1) and (2)

<form:form modelAttribute = "prodotto" ...>
    ....
    <form:errors path="codice" />
    ...
</form:form>

or configure command as an attribute name in point (3)

@ModelAttribute("command") Prodotto prod

If you don't have any messages.properties file I would expect there to be an error message in the logs because it can't find any message under the code "Il codice e richiesto".