JDOM修改Xml保存失败

Question

哪位高人帮忙看一下以下代码，为什么不能修改xml 的内容呢。 public void saveXml(XmlObject xmlobj) throws JDOMException, FileNotFoundException {
        SAXBuilder builder = new SAXBuilder();
        FileInputStream fi = null;
        FileOutputStream fo = null;
        fi = new FileInputStream(xmlUrl);
        Document doc;
        try {
            doc = builder.build(fi);
            Element root = doc.getRootElement();
            List oralist = root.getChildren("ORAJDBC");
            Iterator oraitems = oralist.iterator();
            while (oraitems.hasNext()) {
                Element orachild = (Element) oraitems.next();
                orachild.getChild("DBHOST").setText(xmlobj.getOraHost());
                orachild.getChild("DBPORT").setText(xmlobj.getOraPort());
                orachild.getChild("DBUSER").setText(xmlobj.getOraUser());
                orachild.getChild("DBPWD").setText(xmlobj.getOraPsd());
                orachild.getChild("DBSID").setText(xmlobj.getOraDb());
            }            List sqlList = root.getChildren("SQLJDBC");
            Iterator sqlitems = sqlList.iterator();
            while (sqlitems.hasNext()) {
                Element sqlchild = (Element) sqlitems.next();
                sqlchild.getChild("DBHOST").setText(xmlobj.getOraHost());
                sqlchild.getChild("DBPORT").setText(xmlobj.getSqlPort());
                sqlchild.getChild("DBUSER").setText(xmlobj.getSqlUser());
                sqlchild.getChild("DBPWD").setText(xmlobj.getSqlPsd());
                sqlchild.getChild("DBSID").setText(xmlobj.getSqlDb());
            }
            XMLOutputter outp = new XMLOutputter();
            fo = new FileOutputStream(xmlUrl);
            outp.output(doc, fo);
        } catch (IOException ex) {
            System.err.println(ex + "error");
        }
    }