XPATH sửa XML

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package xulyxml;

import com.sun.org.apache.xml.internal.serialize.OutputFormat;
import com.sun.org.apache.xml.internal.serialize.XMLSerializer;
import java.io.FileOutputStream;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;

public class XPathDemo {

    public static void main(String[] args) throws Exception {

        InputSource xml = new InputSource("MalwareData.xml");
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse(xml);

        XPathFactory xpf = XPathFactory.newInstance();
        XPath xpath = xpf.newXPath();
        String exp = "/malware/timestamp";



        NodeList names = (NodeList) xpath.evaluate(exp, doc, XPathConstants.NODESET);

        for (int i = 0; i < names.getLength(); i++) {
            Element elem = (Element) names.item(i);

            //get current date time with Date()
            Date date = new Date();
            DateFormat dateFormat = new SimpleDateFormat("HH:mm:ss dd/MM/yyyy");
            String timeCurrent = dateFormat.format(date);

            // Sua file MalwareData.xml
            names.item(i).setTextContent(timeCurrent);
            System.err.println(elem.getTextContent());
        }



        //Kết quả trả về là UtCung
        //Ghi file xml

        FileOutputStream output = new FileOutputStream("MalwareData.xml");
        XMLSerializer ser = new XMLSerializer(output, new OutputFormat(doc, "UTF-8", true));
        ser.serialize(doc);
        output.close();
    }
}