code: public String formatMessage(String key, Object[] args) {
          assert _resourceProvider != null : "Received a null resource provider";
          return _resourceProvider.formatMessage(key, args);
      }
docs: Format a message given a resource string name <code>key</code> and a set of
  formatting arguments <code>args</code>.
  @param key the message key
  @param args the arguments used when formatting the message
  @return the formatted message