ajax实现不了表单提交

Question

<div class="modal fade" id="o_info">
    <div class="modal-dialog">
        <div class="modal-content">
            <div class='modal-header'>
                <h4 class="modal-title">审核日志<small></small></h4>
                <button type="button" class="close" data-dismiss="modal"><span
                        aria-hidden="true">&times;</span><span class="sr-only">Close</span></button>

            </div>
            <form class='modal-body form-horizontal' id='b_content'>
                <div class="form-group">
                    <label for="offlineApplicationId" class="col-sm-3 control-label">原因</label>
                    <div class="col-sm-8">
                        <input type="text" class="form-control" id="offlineApplicationId" name='reason' placeholder="xxxxx"
                               data-tree='name'/>
                    </div>
                </div>
            </form>
            <div class='modal-footer'>
                <button id='save' class='btn btn-primary'>保存</button>
                <button type="button" class="btn btn-default" data-dismiss="modal">关闭</button>
            </div>
        </div>
    </div>
</div>

 var ca = null;
    $("#save").click(function () {
        var bootstrapValidator = $('#o_info').data('bootstrapValidator');
        if (bootstrapValidator && !bootstrapValidator.isValid()) {
            swa_err('数据格式不正确');
            return false;
        }
        var url = "/platform/order/reasonOfflineApplication", str = "确认提交", data = $("#b_content").mySerializeObject();
        data.id = ca.id;
        var a = $(this);
        swa_cf4ajax(str, "操作不可撤销", function () {
            a.button('loading');
            $.ajax({
                url: url,
                type: 'POST',
                dataType: 'json',
                data: data,
                error: function (data) {
                    swa_err('Server(' + url + ') is not avaliable.' + data.toString());
                },
                success: function (data) {
                    if (!data.success)
                        swa_err(data.prompt);
                    else {
                        swa_suc("已保存");
                        bTable.ajax.reload(null, false);
                        $("#o_info").modal("hide");
                    }
                }
            }).always(function () {
                a.button('reset');
            });
        });
    });

 @RequestMapping(value = "/order/reasonOfflineApplication", produces = "application/json")
    @ResponseBody
    public DataModel reasonOfflineApplication(OfflineApplicationForm form) {
        try {
            return offlineApplicationService.addReason(form);
        } catch (Exception e) {
            return DataModel.getFailDataModalNotException(e.getMessage());
        }
    }

Headers form data   id和reason数据都有而且正常，但就是200然后json有问题