//数组转换成xml  
    protected function arrayToXml($arr){
        $xml = "";
        foreach ($arr as $key => $val) {  
            if (is_array($val)) {  
                $xml .= "<" . $key . ">" . arrayToXml($val) . "";  
            } else {
                $xml .= "<" . $key . ">" . $val . "";  
            }
        }
        $xml .= "";  
        return $xml;  
    }
    //xml转换成数组  
    protected function xmlToArray($xml) {  
        //禁止引用外部xml实体   
        libxml_disable_entity_loader(true);  
        $xmlstring = simplexml_load_string($xml, 'SimpleXMLElement', LIBXML_NOCDATA);  
        $val = json_decode(json_encode($xmlstring), true);  
        return $val;  
    }