struts2的攔截器攔截ajax請求

攔截器代碼：
@Override
public String intercept(ActionInvocation invocation) throws Exception {

ActionContext ctx = invocation.getInvocationContext();
Map session = ctx.getSession();
User user = (User) session.get(Constants.SESSION_USER_KEY);
if (user == null) {
HttpServletRequest request = ServletActionContext.getRequest();
HttpServletResponse response = ServletActionContext.getResponse();
PrintWriter pw = response.getWriter();

String flag = "";

//對ajax請求的攔截 if (request.getHeader("X-Requested-With") != null
&& request.getHeader("X-Requested-With").equalsIgnoreCase(     
"XMLHttpRequest")) {  
log.info("使用者沒登入或登入到期，不能訪問");
response.setCharacterEncoding("text/html;charset=utf-8");
response.setContentType("text/html;charset=utf-8");
flag = "9999";
pw.write(flag);

return null;

//不是非同步請求的攔截 } else {
response.setCharacterEncoding("text/html;charset=utf-8");
response.sendRedirect("/businessTest/login.jsp");
log.info("使用者沒登入或登入到期，不能訪問");
return "login";
}
}
return invocation.invoke();

}

jsp頁面代碼

// 登入驗證 
Ext.Ajax.on('requestcomplete',checkUserSessionStatus, this);   //所有的非同步請求都會走的事件
function checkUserSessionStatus(conn,response,options){
var str = response.responseText;
if(str == '9999'){
alert('串連已逾時,請重新登入!');
window.location.href = 'login.jsp';
}
}