Extjs与struts2整合，ajax请求登录验证

if (user == null) {
HttpServletRequest request = ServletActionContext.getRequest();
HttpServletResponse response = ServletActionContext.getResponse();
PrintWriter pw = response.getWriter();
String flag = "";
if (request.getHeader("X-Requested-With") != null
&& request.getHeader("X-Requested-With").equalsIgnoreCase(
"XMLHttpRequest")) {
log.info("用户没登录或登录过期，不能访问");
response.setCharacterEncoding("text/html;charset=utf-8");
response.setContentType("text/html;charset=utf-8");
flag = "9999";
pw.write(flag);
return null;
} else {
response.setCharacterEncoding("text/html;charset=utf-8");
response.sendRedirect("/businessTest/login.jsp");
log.info("用户没登录或登录过期，不能访问");
return "login";
}
}

Ext.Ajax.on('requestcomplete',checkUserSessionStatus, this);
function checkUserSessionStatus(conn,response,options){
var str = response.responseText;
if(str == '9999'){
alert('连接已超时,请重新登录!');
window.location.href = 'login.jsp';
}
}