Spring MVC表单：使用Ajax的错误

Question

I have a question related to Spring 3 MVC, Ajax, and form:errors.

I have a form I am submitting to the server and I am using Spring MVC. I have all the validation, controllers, etc set up and working fine. When I submit data that fails validation, I get the error message coming back and being displayed on the form as per my form:errors tags in my jsp.

My question is...

If I want to convert over to an Ajax approach, can I still take advantage of all the infrastructure of a "normal" Spring MVC app (ie, specifically the validator and form:errors features) to get the errors back to (and displayed on) the browser? I see how to submit Ajax requests, but I don't see how (or if) I can still utilize the form:errors capability of the jsp.

Does anyone know if this can be done, and if so, point me in the appropriate general direction?

Thanks in advance.

Answer 1

You can't, since tags like <form:errors> are evaluated server-side and embed error messages/elements in the HTML content of the HTTP response. Since an AJAX request to the server typically returns XML or JSON to a response (and not HTML), which is then parsed by client-side JavaScript, there is no point at which Spring can bind to the request/form and add error messages to the content.

Answer 2

I have used quite a lot of AJAX when submitting forms in Spring. Basically what I have done is that I have created a form.jsp file which I then return from the AJAX call. Since the AJAX will return the whole form with all the form tags available, I get the full benefit of server side validation.

So, if I have a page that contains a form, I could, for example, have a div that acts as the form container

<div id="form-container">
    <form id="myform">
        Normal form here ...
    </form>
</div>

And when I submit the form, I could load the form.jsp by using jQuery, for example,

$('#myform').submit(function() {
    $('#form-container').load('ajax/somehandler');
});

So, all you have to do is to return the form.jsp from the controller with all the normal bindings as you would have with non-AJAX approach as well. Do you get the idea?

Answer 3

Not really, no. The form:error tag does its magic when the page is first generated server-side. If you're not re-generating the page serverside, because you used ajax, none of that is going to run. The Errors object itself isn't really returnable all the way back to the client. You could serialize it to JSON I suppose, but there's an awful lot of stuff in there that you don't need. Plus of course it usually only has codes, not actual messages, on it and needs the message source to look up the translations.

Bottom line, you'll need to send the errors manually and handle setting the error messages yourself in javascript when you get back the ajax response.