How do I insert value in to xml tag

I have the following xml file:

<?xml version="1.0"?>
<SMS>
    <ALERTS>
        <SNO>1</SNO> 
        <MOBILENUMBER>1234567890</MOBILENUMBER> 
        <TEXT>HI</TEXT> 
        <TIME></TIME> 
        <RESPONSEID></RESPONSEID>
    </ALERTS>       
</SMS>

I would like to insert string value into XML Tag(RESPONSEID). I have tried with setTextContent and setNodeValue methods which didn't work for me.

Following is my little program:

public void selectRecords() throws SQLException
{
    File file = new File("E:\\Workspace\\netbeans-workspace\\DOM_Parser_Sample\\MyXMLFile1.xml");
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    DocumentBuilder db = dbf.newDocumentBuilder();
    Document doc = db.parse(file);
    doc.getDocumentElement().normalize();
    NodeList nodeList = doc.getElementsByTagName("ALERTS");
    for (int s = 0; s < nodeList.getLength(); s++) 
    {
    Node firstNode = nodeList.item(s);

        if (firstNode.getNodeType() == Node.ELEMENT_NODE) 
        {
            Element eElement = (Element) firstNode;
            BufferedReader in = new BufferedReader(new InputStreamReader(httpcon.getInputStream()));
            StringBuffer response = new StringBuffer();
            while ((inputLine = in.readLine()) != null) 
            {
                    res = response.append(inputLine).toString();
            }
            in.close();
           NodeList responseList = eElement.getElementsByTagName("RESPONSEID").item(0).getChildNodes();
           responseList.item(0).setTextContent(res);
        }
    }
}