xml解析,该如何处理

    Document doc = builder.parse(new FileInputStream(new File(
                    filename)));
            NodeList nodes = doc.getElementsByTagName("audio");
            for (int i = 0; i < nodes.getLength(); i++) {
                Element node = (Element) nodes.item(i);
                System.out.println("nuuu");
                userid = "null";
                if( node.getElementsByTagName("userid").item(0).getFirstChild().getNodeValue()!=null)
                    {
                    System.out.println("nuuu");
                    userid = "liming";
                    }