code: @Override
    public String getPrefix(String namespaceURI) {
      // per javax.xml.namespace.NamespaceContext doc
      if (namespaceURI == null)
        throw new IllegalArgumentException("Cannot find prefix for null namespace URI");
      if (XMLConstants.XML_NS_URI.equals(namespaceURI))
        return XMLConstants.XML_NS_PREFIX;
      if (XMLConstants.XMLNS_ATTRIBUTE_NS_URI.equals(namespaceURI))
        return XMLConstants.XMLNS_ATTRIBUTE;
  
      for (Map.Entry<String, String> entry: bindings.entrySet()) {
        if (namespaceURI.equals(entry.getValue()))
          return entry.getKey();
      }
  
      return null;
    }
docs: Returns the prefix for a namespace binding.