使用php检查Ajax dataType

I am using this php function which checks if the request is an Ajax request or not which works fine.

function ajax_check() {
    if(!empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
        return TRUE;
    } else {
        return FALSE;
    }
}

I want to know the dataType of the Ajax request. For example if the dataType is json or not. How can i achieve this using php?

You can check it in request headers

Accept application/json, text/javascript, /; q=0.01

there will be "text/html" or application/json