public String getPositionsAsXML() {
    ArrayList<Position> pList = new ArrayList<Position>(positionMap.values());
    Collections.sort(pList);

    StringBuilder xml = new StringBuilder("<positions>");
    for (Position p : pList) xml.append(p.toXML());
    xml.append("</positions>");
    return xml.toString();
  }
 public String getParticipantPositionsAsXML(String pid) {
   Set<Position> posSet = getParticipantPositions(pid);
   if (posSet != null) {
     String header = String.format("<positions participantid=\"%s\">", pid);
     StringBuilder xml = new StringBuilder(header);
     for (Position p : posSet) xml.append(p.toXML());
     xml.append("</positions>");
     return xml.toString();
   } else return ("<positions/>");
 }