Zookeeper.java

package fds.zookeeper.toto;

import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

import java.io.IOException;
import java.util.concurrent.CountDownLatch;
import java.util.function.Consumer;

import static java.lang.Thread.currentThread;

public class Main {
    private static final String HOST = "localhost";
    private static final String WATCHED_PATH = "/toto";

    public static void main(String[] args) throws IOException, InterruptedException {
        ZooKeeper zooKeeper = connect(HOST);
        watchForever(zooKeeper, WATCHED_PATH, System.out::println);
        currentThread().join();
    }

    private static void watchForever(ZooKeeper zooKeeper, String path, Consumer<WatchedEvent> watcher) {
        try {
            zooKeeper.exists(path, event -> {
                watchForever(zooKeeper, path, watcher);
                watcher.accept(event);
            });
        } catch (KeeperException | InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

    private static ZooKeeper connect(String host) throws IOException, InterruptedException {
        CountDownLatch connectionLatch = new CountDownLatch(1);
        ZooKeeper zoo = new ZooKeeper(host, 2000, event -> {
            System.out.println(event);
            if (event.getState() == Watcher.Event.KeeperState.SyncConnected) {
                connectionLatch.countDown();
            }
        });
        connectionLatch.await();
        return zoo;
    }
}