js-datatable无法发送ajax

<code> JS脚本如下：<script type="text/javascript">//<![CDATA[  $(document).ready(function(){    $('#tpval').focus();    var s = document.getElementById('num');    if (typeof(s) != "undefined") {      $('#num').focus();    }            $.extend( true, $.fn.dataTable.defaults, {                "bFilter": false,                } );            $('#datastable').dataTable({                "bStateSave": true,                "bProcessing": true,                "bServerSide": true,              "sAjaxSource": "/webadmin/idxg.php?gmd=pay.lists&ajax=1",                "sServerMethod": "POST",                "bJQueryUI": true,                "sPaginationType": "full_numbers",                "fnRowCallback": function( nRow, aData, iDisplayIndex ) {                    /* Append the grade to the default row class name */                       switch ( aData[11] ) {                        case "1": /* 退单 */                            $("td", nRow).each(function (){$(this).wrapInner("<font style='color:#ff0000;'><\/font>");});                            break;                        case "2": /* 测试单 */                            $("td", nRow).each(function (){$(this).wrapInner("<font style='color:#ff9000;'><\/font>");});                            break;                    }                    return nRow;                },                "aoColumnDefs": [                  { "bSortable": false, "aTargets": [ 0 ] }                ],                "aaSorting": [[ 1, 'asc' ]]            });          });//]]></script>服务端：public function lists()    {        $pri = self::_check_pri(array(44,59,66));        **$ajax = getgpc('ajax','G');**        //接收待查询、显示的数据库字段        $select_keys = array(' ', 'pay_id','transaction_type','transaction_id','receiver_id','pay_type','pay_money','pay_date','order_state','order_money','order_id','order_date','check_date','buyer_id');        // ajax请求        if ($ajax) {            if (!is_array($pri) || (!$pri[44] && !$pri[66])) {                exit;            }            $pay_hide = 0;            if ($pri[59]) {                $pay_hide = 1;            }            self::_lists_ajax($select_keys, $pay_hide);        }                现象：在服务端打印$ajax为NULL，不懂得该如何调试从前端到服务端过程中是否有ajax通信</code>