public function encode($data, array $config = [])
{
//初始化配置
$config = array_merge($this->config, $config);
//创建XML对象
$xml = new \SimpleXMLElement("<{$config['root_name']}></{$config['root_name']}>");
self::data2xml($xml, $data, $config['item_name'], $config['item_key']);
return $xml->asXML();
}