Changing /updating an xml file using JAXP(DOM)

Question

Hello,
i am fairly new to xml and am using it in my degree project.I am able to retrieve and read data from a fairly large xml file using JAXP(DOM) and/or XMLBeans.I am having difficulties in updating the xml document. Any updation i believe is ito be saved into a new xml document,but dont know how to proceed with it. Any help would be appreciated.
Following is a snippet of my code using JAXP. Here i am able to retrieve data from the source file.
File document=new File("C:\\tester.xml");
try {
DocumentBuilderFactory factory
= DocumentBuilderFactory.newInstance();
DocumentBuilder parserr = factory.newDocumentBuilder();
Document doc=parserr.parse(document);
System.out.println(document + " is well-formed.");
NodeList n2=doc.getElementsByTagName("Top");
NodeList n3=doc.getElementsByTagName("Base");
int x=n2.getLength();
System.out.println("There are " x "players");
for(int g=0;g<=x;g++)
System.out.println("Top is" + n2.item(g).getFirstChild().getNodeValue()+" Base is" +n3.item(g).getFirstChild().getNodeValue());
--------------------------------------------------------------------------------

Answer 1

Following is my updation code to the dom tree:
NodeList list=doc.getElementsByTagName("Information");
for(int i=0; i<list.getLength();i++){
Node thissampnode=list.item(i);
Node thisNameNode=thissampnode.getFirstChild();
if(thisNameNode==null) continue;
if(thisNameNode.getFirstChild()==null)continue;
// if(thisNameNode.getFirstChild() !(instanceof org.w3c.dom.Text) continue;
String data=thisNameNode.getFirstChild().getNodeValue();
if (! data.equals("0.59")) continue;
Node newsampNode = doc.createElement("Samp");
Node newsampTopNode = doc.createElement("Top");
Text tnNode = doc.createTextNode("0.50");
newsampTopNode.appendChild(tnNode);
Element newsampRef = doc.createElement("Ref");
Text tsr = doc.createTextNode("0");
newsampRef.appendChild(tsr);
Element newsampType = doc.createElement("Type");
Text tt = doc.createTextNode("z");
newsampType.appendChild(tt);
Element newsampbase = doc.createElement("Base");
Text sb = doc.createTextNode("0.55");
newsampbase.appendChild(sb);
newsampNode.appendChild(newsampTopNode);
newsampNode.appendChild(newsampRef);
newsampNode.appendChild(newsampType);
newsampNode.appendChild(newsampbase);
rootNode.insertBefore(newsampNode, thissampnode);
Here i dont see any changes to the original xml source file.