var xhr = new XMLHttpRequest();
xhr.open("get",remoteUrl);
xhr.setRequestHeader("X-Requested-With","XMLHttpRequest");
xhr.onload = function(){};
xhr.send();

public static boolean isAjax(HttpServletRequest request) {
   return request.getHeader("x-requested-with") != null && 
          request.getHeader("x-requested-with").equalsIgnoreCase("XMLHttpRequest");
}