@Override
 public void addElement(
     StringBuilder buf, Date date, Request request, Response response, long time) {
   if (null != response) {
     Iterator<String> iter = response.getHeaders(header).iterator();
     if (iter.hasNext()) {
       StringBuilder buffer = new StringBuilder();
       boolean first = true;
       while (iter.hasNext()) {
         if (!first) {
           buffer.append(",");
         }
         buffer.append(iter.next());
       }
       buf.append(wrap(buffer.toString()));
     }
     return;
   }
   buf.append("-");
 }
 @Override
 public Collection<String> getHeaders(String name) {
   return response.getHeaders(name);
 }