Pass array into Spring MVC by AJAX

Question

I'm working on spring mvc application, where I should aplly validation based on Spring MVC validator but validate but AJAX request. So, when I send just single data everything is ok, Spring is mapping data from request into object and validate it. But when I add new paramener which is array, Spring thows a exception:

java.lang.NumberFormatException: For input string: ""

My User class:

public class User
{
    @NotEmpty
    private String login;

    private List<Department> departments;
}

My controller:

@Controller
public class UserController
{
    @RequestMapping(value = "/save")
    public ModelAndView save(@Valid @ModelAttribute("user") final User user,
            BindingResult result) throws Exception
    {
       // do action
    }
}

My AJAX request(POST):

http://localhost:8080/myApp/user/save?departments%5B%5D=1&departments%5B%5D=3&id=&login=Test

My JS(jQuery):

var form = $('.add-form');
var fields = form.find('input');
var data = {};
// get valud from input fields
for (var i = 0; i < fields.length; i++) {
    var $item = $(fields[i]);
    data[$item.attr('name')] = $item.val();
}
// get value from list as array
data['departments'] = form.find('#departmentsSelector').val();
$.ajax({
    type: "POST",
    url: "user/save",
    data: data,
    success: function(response){
        // do something
    }
})

It looks like Spring is trying to parse name of parameter departments[] as a parameter with a value instead of use value of this parameter.

Can anyone help me with this?

Answer 1

So, I've found an error, the problem was in [] for parameter departments. If you use traditional: true for jQuery AJAX request than array variable will not contain [] in name and Spring mapping it in POJO.