Create and add Attribute to an Element

import java.io.StringWriter;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.DOMImplementation;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

public class Main {
  public static void main(String[] argv) throws Exception {
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    DocumentBuilder builder = factory.newDocumentBuilder();
    DOMImplementation impl = builder.getDOMImplementation();
    Document doc = impl.createDocument(null, null, null);
    Element e1 = doc.createElement("api");
    doc.appendChild(e1);
    Element e2 = doc.createElement("java");
    e1.appendChild(e2);

    e2.setAttribute("url", "http://www.domain.com");
    DOMSource domSource = new DOMSource(doc);
    Transformer transformer = TransformerFactory.newInstance().newTransformer();
    StringWriter sw = new StringWriter();
    StreamResult sr = new StreamResult(sw);
    transformer.transform(domSource, sr);
    System.out.println(sw.toString());
  }
}