import java.io.File;
import java.io.StringReader;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.DocumentFragment;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.xml.sax.InputSource;
public class Main {
public static void main(String[] argv) throws Exception {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(true);
Document doc = factory.newDocumentBuilder().parse(new File("infilename.xml"));
String fragment = "aaa";
factory = DocumentBuilderFactory.newInstance();
Document d = factory.newDocumentBuilder().parse(new InputSource(new StringReader(fragment)));
Node node = doc.importNode(d.getDocumentElement(), true);
DocumentFragment docfrag = doc.createDocumentFragment();
while (node.hasChildNodes()) {
docfrag.appendChild(node.removeChild(node.getFirstChild()));
}
Element element = doc.getDocumentElement();
element.appendChild(docfrag);
}
}