// 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 }/";
    	}
    }
});