后端过滤器处理：
// 处理Ajax请求
HttpServletResponse response = (HttpServletResponse) arg1;
if ("XMLHttpRequest".equalsIgnoreCase(request.getHeader("X-Requested-With"))) {
response.setCharacterEncoding("UTF-8");
response.getWriter().write("{\"status\": 302,\"msg\": \"请先登录！\"}");
} else {
response.sendRedirect(request.getcontextpath() + "/index.jsp");
}
前端处理（Ajax全局设置）：
$.ajaxSetup({
complete: function(r,status) {
var json = JSON.parse(r.responseText);
if(json.status == 302){
top.location.href = "${pageContext.request.contextpath }/";
}
}
});