layui upload如何使用csrf 400 请求报错 

在使用layui upload的时候，被csrf拦截，各位大大侠们，这个要怎么解决？
一｜页面代码

<!--  security csrf  --> <meta name="_csrf" th:content="${_csrf.token}"/> <!-- default header name is X-CSRF-TOKEN --> <meta name="_csrf_header" th:content="${_csrf.headerName}"/>

<!-- layui -->
<link type="text/css" rel="stylesheet" href="../../public/front/js/lib/layui/css/layui.css"
      th:href="@{/front/js/lib/layui/css/layui.css}"/>
<script type="text/javascript" src="../../public/front/js/lib/layui/layui.js"
        th:src="@{/front/js/lib/layui/layui.js}"></script>

<!-- ajax security -->
<script type="text/javascript">
    $(function () {
        var token = $("meta[name='_csrf']").attr("content");
        var header = $("meta[name='_csrf_header']").attr("content");
        $(document).ajaxSend(function (e, xhr, options) {
            xhr.setRequestHeader(header, token);
        });
    });

    layui.use('upload', function () {
        layui.upload({
            url: "file/upload/single.htm"
            , success: function (res) {
                console.log(res); //上传成功返回值，必须为json格式
            }
        });
    });
</script>

<div class="layui-box layui-upload-button"> <form target="layui-upload-iframe" method="post" key="set-mine" enctype="multipart/form-data" th:action="@{/file/upload/single.htm}"> <input type="file" name="file" class="layui-upload-file"></form> <span class="layui-upload-icon"><i class="layui-icon"></i>上传图片</span> </div>

二｜下面是正常用上传文件的请求
三｜用layui upload上传文件的请求

_csrf这个参数没传过去，导致直接都被拦截了，这个要怎么搞呀，各位大大侠们？
layui的里提问的地址
http://fly.layui.com/jie/5228.html