header('Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
	header('Cache-Control: must-revalidate');
	header('Expires: 0');
	header('Pragma: public');
	header('Content-Disposition: attachment; filename="' . $fileName.'.'.$fileExtension . '"');	
	
	echo $file;
	
	if (ob_get_contents() || ob_get_length()) {
	  ob_end_clean(); //or ob_end_flush();
	}

	exit();

如果内容$file是 base64 编码，则应更改echo $file为echo base64_decode($file);