判断是否为ajax请求

if (request.getHeader("x-requested-with") != null 
&& request.getHeader("x-requested-with").equalsIgnoreCase("XMLHttpRequest")) { 
out.print("该请求是 AJAX 异步HTTP请求。"); 
}else{ 
out.print("该请求是传统的 同步HTTP请求。"); 
}