$ ZOOBINDIR=${ZK_HOME}/bin
$ source ${ZOOBINDIR}/zkEnv.sh

$ echo $CLASSPATH 
/usr/share/zookeeper-3.4.6/bin/../build/classes :/usr/share/zookeeper-3.4.6/bin/../build/lib/*.jar :/usr/share/zookeeper-3.4.6/bin/../lib/slf4j-log4j12-1.6.1.jar :/usr/share/zookeeper-3.4.6/bin/../lib/slf4j-api-1.6.1.jar :/usr/share/zookeeper-3.4.6/bin/../lib/netty-3.7.0.Final.jar :/usr/share/zookeeper-3.4.6/bin/../lib/log4j-1.2.16.jar :/usr/share/zookeeper-3.4.6/bin/../lib/jline-0.9.94.jar :/usr/share/zookeeper-3.4.6/bin/../zookeeper-3.4.6.jar :/usr/share/zookeeper-3.4.6/bin/../src/java/lib/*.jar :/usr/share/zookeeper-3.4.6/bin/../conf:

/*Our First ZooKeeper Program*/
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.ZooKeeper;
public class HelloZooKeeper {
public static void main(String[] args) throws IOException {
String hostPort = "localhost:2181";
String zpath = "/";
List <String> zooChildren = new ArrayList<String>();
ZooKeeper zk = new ZooKeeper(hostPort, 2000, null);
if (zk != null) {
try {
zooChildren = zk.getChildren(zpath, false);
System.out.println("Znodes of '/': ");
for (String child: zooChildren) {
//print the children
System.out.println(child);
}
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}

ZooKeeper(String connectString, int sessionTimeout, Watcher watcher)

ZooKeeper(String connectString, int sessionTimeout, Watcher watcher, boolean canBeReadOnly)

ZooKeeper(String connectString, int sessionTimeout, Watcher watcher, long sessionId, byte[] sessionPasswd)

ZooKeeper(String connectString, int sessionTimeout,Watcher watcher, long sessionId, byte[] sessionPasswd,boolean canBeReadOnly)

zooChildren = zk.getChildren(zpath, false)

$ javac -cp $CLASSPATH HelloZooKeeper.java

$ ${ZK_HOME}/bin/zkServer.sh start

$ java -cp $CLASSPATH HelloZooKeeper

$ $ZK_HOME/bin/zkCli.sh -server localhost

public interface Watcher {
void process(WatchedEvent event);
}

import java.io.IOException;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;
public class DataWatcher implements Watcher, Runnable {
private static String hostPort = "localhost:2181";
private static String zooDataPath = "/MyConfig";
byte zoo_data[] = null;
ZooKeeper zk;

public DataWatcher() {
try {
zk = new ZooKeeper(hostPort, 2000, this);
if (zk != null) {
try {
//Create the znode if it doesn't exist, with the following code:
if (zk.exists(zooDataPath, this) == null) {
zk.create(zooDataPath, "".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
}
} catch (KeeperException | InterruptedException e) {
e.printStackTrace();
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
public void printData() throws InterruptedException, KeeperException {
zoo_data = zk.getData(zooDataPath, this, null);
String zString = new String(zoo_data);
// The following code prints the current content of the znode to the console:
System.out.printf("\nCurrent Data @ ZK Path %s: %s", zooDataPath, zString);
}
@Override
public void process(WatchedEvent event) {
System.out.printf(
"\nEvent Received: %s", event.toString());
//We will process only events of type NodeDataChanged
if (event.getType() == Event.EventType.NodeDataChanged) {
try {
printData();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args)
throws InterruptedException, KeeperException {
DataWatcher dataWatcher = new DataWatcher();
dataWatcher.printData();
dataWatcher.run();
}
public void run() {
try {
synchronized (this) {
while (true) {
wait();
}
}
} catch (InterruptedException e) {
e.printStackTrace();
Thread.currentThread().interrupt();
}
}
}

if (zk.exists(zooDataPath, this) == null) {

zk.create(zooDataPath, "".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

public void process(WatchedEvent event) {

if (event.getType() == Event.EventType.NodeDataChanged)

zoo_data = zk.getData(zooDataPath, this, null);

import java.io.IOException;
import java.util.UUID;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
public class DataUpdater implements Watcher {
private static String hostPort = "localhost:2181";
private static String zooDataPath = "/MyConfig";
ZooKeeper zk;
public DataUpdater() throws IOException {
try {
zk = new ZooKeeper(hostPort, 2000, this);
} catch (IOException e) {
e.printStackTrace();
}
}

// updates the znode path /MyConfig every 5 seconds with a new UUID string.
public void run() throws InterruptedException, KeeperException {
while (true) {
String uuid = UUID.randomUUID().toString();
byte zoo_data[] = uuid.getBytes();
zk.setData(zooDataPath, zoo_data, -1);
try {
Thread.sleep(5000); // Sleep for 5 secs
} catch(InterruptedException e) {
Thread.currentThread().interrupt();
}
}
}

public static void main(String[] args) throws
IOException, InterruptedException, KeeperException {
DataUpdater dataUpdater = new DataUpdater();
dataUpdater.run();
}
@Override
public void process(WatchedEvent event) {
System.out.printf("\nEvent Received: %s", event.toString());
}
}

$ javac –cp $CLASSPATH DataWatcher.java
$ javac –cp $CLASSPATH DataUpdater.java

$ java –cp $CLASSPATH DataWatcher

$ java -cp $CLASSPATH DataUpdater

import java.io.IOException;
import java.util.List;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
public class ClusterMonitor implements Runnable {
private static String membershipRoot = "/Members";
private final Watcher connectionWatcher;
private final Watcher childrenWatcher;
private ZooKeeper zk;
boolean alive=true;
public ClusterMonitor(String HostPort) throws IOException, InterruptedException, KeeperException {
connectionWatcher = new Watcher() {
@Override
public void process(WatchedEvent event) {
if(event.getType()==Watcher.Event.EventType.None && event.getState() == Watcher.Event.KeeperState.SyncConnected) {
System.out.printf("\nEvent Received: %s", event.toString());
}
}
};
childrenWatcher = new Watcher() {
@Override
public void process(WatchedEvent event) {
System.out.printf("\nEvent Received: %s", event.toString());
if (event.getType() == Event.EventType.NodeChildrenChanged) {
try {
//Get current list of child znode, 
//reset the watch
List<String> children = zk.getChildren( membershipRoot, this);
wall("!!!Cluster Membership Change!!!");
wall("Members: " + children);
} catch (KeeperException e) {
throw new RuntimeException(e);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
alive = false;
throw new RuntimeException(e);
}
}
}
};
zk = new ZooKeeper(HostPort, 2000, connectionWatcher);
// Ensure the parent znode exists
if(zk.exists(membershipRoot, false) == null) {
zk.create(membershipRoot, "ClusterMonitorRoot".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
}

// Set a watch on the parent znode
List<String> children = zk.getChildren(membershipRoot, childrenWatcher);
System.err.println("Members: " + children);
}
public synchronized void close() {
try {
zk.close();
} catch (InterruptedException e) {
e.printStackTrace();
}
}

public void wall (String message) {
System.out.printf("\nMESSAGE: %s", message);
}
public void run() {
try {
synchronized (this) {
while (alive) {
wait();
}
}
} catch (InterruptedException e) {
e.printStackTrace();
Thread.currentThread().interrupt();
} finally {
this.close();
}
}
public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
if (args.length != 1) {
System.err.println("Usage: ClusterMonitor <Host:Port>");
System.exit(0);
}
String hostPort = args[0];
new ClusterMonitor(hostPort).run();
}
}

import java.io.IOException;
import java.lang.management.ManagementFactory;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
public class ClusterClient implements Watcher, Runnable {
private static String membershipRoot = "/Members";
ZooKeeper zk;
public ClusterClient(String hostPort, Long pid) {
String processId = pid.toString();
try {
zk = new ZooKeeper(hostPort, 2000, this);
} catch (IOException e) {
e.printStackTrace();
}
if (zk != null) {
try {
zk.create(membershipRoot + '/' + processId, processId.getBytes(),Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
} catch (
KeeperException | InterruptedException e) {
e.printStackTrace();
}
}
}
public synchronized void close() {
try {
zk.close();
}
catch (InterruptedException e) {
e.printStackTrace();
}
}

@Override
public void process(WatchedEvent event) {
System.out.printf("\nEvent Received: %s", event.toString());
}

public void run() {
try {
synchronized (this) {
while (true) {
wait();
}
}
} catch (InterruptedException e) {
e.printStackTrace();
Thread.currentThread().interrupt();
} finally {
this.close();
}
}
public static void main(String[] args) {
if (args.length != 1) {
System.err.println("Usage: ClusterClient <Host:Port>");
System.exit(0);
}
String hostPort = args[0];
//Get the process id
String name = ManagementFactory.getRuntimeMXBean().getName();
int index = name.indexOf('@');
Long processId = Long.parseLong(name.substring(0, index));
new ClusterClient(hostPort, processId).run();
}
}

$ javac -cp $CLASSPATH ClusterMonitor.java
$ javac -cp $CLASSPATH ClusterClient.java

$ java -cp $CLASSPATH ClusterMonitorlocalhost:2181

$ java -cp $CLASSPATH ClusterClient localhost:2181 2>&1>/dev/null &
[1] 4028
$ java -cp $CLASSPATH ClusterClient localhost:2181 2>&1>/dev/null &
[2] 4045
$ java -cp $CLASSPATH ClusterClient localhost:2181 2>&1>/dev/null &
[3] 4057
$ java -cp $CLASSPATH ClusterClient localhost:2181 2>&1>/dev/null &
[4] 4072
$ java -cp $CLASSPATH ClusterClient localhost:2181 2>&1>/dev/null &
[5] 4084

$ kill -9 4084