code: public synchronized String getNamespaceURIByPrefix(String prefix) throws NamespaceException
     {
        if (!prefixToURI.containsKey(prefix))
        {
           throw new NamespaceException(prefix + ": is not a registered namespace prefix.");
        }
        return prefixToURI.get(prefix);
     }
docs: Returns a namespace uri for a <code>prefix</code>.
  
  @param prefix the namespace prefix.
  @return the namespace uri.
  @throws NamespaceException if no namespace uri is registered for
  <code>prefix</code>.