public static function download_excel($filename, $head_array, $datalist)
{
$output = "<HTML>";
$output .= "<HEAD>";
$output .= "<META http-equiv=Content-Type content=\"text/html; charset=utf-8\">";
$output .= "</HEAD>";
$output .= "<BODY>";
$output .= Excel::arr_tbl_excel($head_array, $datalist);
$output .= "</BODY>";
$output .= "</HTML>";
header("Content-type:application/msexcel");
header("Content-disposition: attachment; filename={$filename}.xls");
header("Cache-control: private");
header("Pragma: private");
print $output;
}