XML - StandAlone

Programação Java
#1

Estou precisando set no xml o standalone para yes.
meu código esta assim:

import org.dom4j.Document;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.XMLWriter;

...

Document document = DocumentHelper.createDocument();

Element dataPacket = document.addElement("DATAPACKET");
dataPacket.addAttribute("Version", "2.0");

Element metadata = dataPacket.addElement("METADATA");

...

Writer str = new java.io.StringWriter();
writer = new XMLWriter();

OutputFormat formatXML = new OutputFormat.createPrettyPrint();
formatXML.setEncoding("UTF-8");
formatXML.setTrimText(false);
formatXML.setNewLineAfterDeclaration(false);
writer = new XMLWriter(str, formatXML);
writer.write(document);

System.out.println(str.toString());

entretanto a saída esta:

<?xml version="1.0" encoding="UTF-8"?>
<DATAPACKET Version="2.0">
  <METADATA>
  </METADATA>
</DATAPACKET>

como faço para colocar o standalone ?

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
#2