spring mvc session超时js监听为什么把 complete换成 beforeSend就不执行 了！

    //全局的ajax访问，处理ajax清求时sesion超时

    $(function () {

        var pathName = window.document.location.pathname;

        var projectName = pathName.substring(0, pathName.substr(1).indexOf('/') + 1);

        $.ajaxSetup({

            contentType: "application/x-www-form-urlencoded;charset=utf-8",

            complete: function (XMLHttpRequest) {

                //XMLHttpRequest.abort();

                var sessionstatus = XMLHttpRequest.getResponseHeader("sessionstatus"); //通过XMLHttpRequest取得响应头，sessionstatus，

                if (sessionstatus == "timeout") {

                    //如果超时就处理 ，指定要跳转的页面

                    alert("登录超时,请重新登录！");

                    window.location.replace(projectName + "/user/login");

                }





            }

        });

    });