POST JSON 失败，415 Unsupported media type, Spring 3 mvc

我正在尝试向 servlet 发送 POST 请求.请求通过 jQuery 以这种方式发送:

I am trying to send a POST request to a servlet. Request is sent via jQuery in this way:

var productCategory = new Object();
productCategory.idProductCategory = 1;
productCategory.description = "Descrizione2";
newCategory(productCategory);

newCategory 在哪里

where newCategory is

function newCategory(productCategory)
{
  $.postJSON("ajax/newproductcategory", productCategory, function(
      idProductCategory)
  {
    console.debug("Inserted: " + idProductCategory);
  });
}

和 postJSON 是

and postJSON is

$.postJSON = function(url, data, callback) {
    return jQuery.ajax({
    'type': 'POST',
    'url': url,
    'contentType': 'application/json',
    'data': JSON.stringify(data),
    'dataType': 'json',
    'success': callback
    });
};

使用 firebug 我看到 JSON 发送正确:

With firebug I see that JSON is sent correctly:

{"idProductCategory":1,"description":"Descrizione2"}

但我得到 415 Unsupported media type.Spring mvc 控制器有签名

But I get 415 Unsupported media type. Spring mvc controller has signature

    @RequestMapping(value = "/ajax/newproductcategory", method = RequestMethod.POST)
public @ResponseBody
Integer newProductCategory(HttpServletRequest request,
        @RequestBody ProductCategory productCategory)

几天前它有效，现在它不是.如果需要，我会显示更多代码.谢谢

Some days ago it worked, now it is not. I'll show more code if needed. Thanks