import java.io.File;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;
public class Main {
public static void main(String[] argv) throws Exception{
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(true);
factory.setExpandEntityReferences(false);
Document doc = factory.newDocumentBuilder().parse(new File("filename"));
Element element = doc.getElementById("key1");
NamedNodeMap attrs = element.getAttributes();
while (attrs.getLength() > 0) {
attrs.removeNamedItem(attrs.item(0).getNodeName());
}
}
}