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//create a new Document
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
Document d = db.newDocument();

//add root Node
Element noteuser = d.createElement("note-users");
d.appendChild(noteuser);

//add exists Node
Document readXML = db.parse(new File("c:\\note-user.xml"));
NodeList nl = readXML.getElementsByTagName("user");
for(int i = 0; i < nl.getLength(); i++)
{
Element n = d.createElement("user");
n.setAttribute("name", nl.item(i).getAttributes().getNamedItem("name").getNodeValue());
if(id !=null && id.equals(nl.item(i).getAttributes().getNamedItem("name").getNodeValue()))
{
//duplicate id (redirect to error page)
response.getWriter().print("<font color = red>duplicate id !</font>");
response.getWriter().print("      ");
response.getWriter().print("<a href = \"reg.jsp\">return to login page</a>");
return;
}
n.setAttribute("password", nl.item(i).getAttributes().getNamedItem("password").getNodeValue());
noteuser.appendChild(n);
}

//add regist Node
Element n = d.createElement("user");
n.setAttribute("name", id);
n.setAttribute("password", pwd);
noteuser.appendChild(n);

//save data to file
TransformerFactory tFactory = TransformerFactory.newInstance();
Transformer transformer = tFactory.newTransformer();
DOMSource source = new DOMSource(d);

//file's path
StreamResult result = new StreamResult(new File("c:\\note-user.xml"));
transformer.transform(source, resu