code: private void doSelectGroup(final Message<JsonObject> message) {
      final Object key = message.body().getValue("key");
      if (key == null) {
        message.reply(new JsonObject().putString("status", "error").putString("message", "No key specified."));
      } else {
        selectGroup(key, new Handler<AsyncResult<String>>() {
          @Override
          public void handle(AsyncResult<String> result) {
            if (result.failed()) {
              message.reply(new JsonObject().putString("status", "error").putString("message", result.cause().getMessage()));
            } else if (result.result() == null) {
              message.reply(new JsonObject().putString("status", "error").putString("message", "No groups to select."));
            } else {
              message.reply(new JsonObject().putString("status", "ok").putString("result", result.result()));
            }
          }
        });
      }
    }
docs: Selects a group in the cluster.