java Servlet Filter 拦截Ajax请求

String requestType = request.getHeader("X-Requested-With");//请求类型 判定是否为ajax请求
if("XMLHttpRequest".equalsIgnoreCase(requestType)){//ajax请求
      response.setHeader("sessionstatus", "timeout");  
      response.sendError(518, "session timeout.");  
}

//ajax请求登录验证
$.ajaxSetup({
    type: ‘POST‘,
    complete: function(xhr,status) {
	    var sessionStatus = xhr.getResponseHeader(‘sessionstatus‘);
		if(sessionStatus == ‘timeout‘) {
			$.messager.alert("登录失效","由于您长时间未操作,登录已失效,请重新登录","info",function(){
				parent.location.href = "login.html";
			});   
		}
    }
});