@Override
      protected void doExec(ZooKeeper zk) {
        zk.exists(path, false, (rc, path, ctx, stat) -> onComplete(zk, rc, stat, false), null);
      }
A very simple read only zookeeper implementation without watcher support.
hbase-client/src/main/java/org/apache/hadoop/hbase/zookeeper/ReadOnlyZKClient.java