public void start() throws KeeperException {
    watcher.registerListener(this);
    // make sure the base node exists
    ZKUtil.createWithParents(watcher, keysParentZNode);

    if (ZKUtil.watchAndCheckExists(watcher, keysParentZNode)) {
      List<ZKUtil.NodeAndData> nodes =
        ZKUtil.getChildDataAndWatchForNewChildren(watcher, keysParentZNode);
      refreshNodes(nodes);
    }
  }
Synchronizes token encryption keys across cluster nodes.
hbase-server/src/main/java/org/apache/hadoop/hbase/security/token/ZKSecretWatcher.java