一、Zookeeper原生API如何进行调用

准备工作：

首先在新建一个maven项目ZK-Demo,然后在pom.xml里面引入zk的依赖

    <dependency>

      <groupId>org.apache.zookeeper</groupId>

      <artifactId>zookeeper</artifactId>

      <version>3.4.10</version>

    </dependency>

1. 连接zk并监听事件

package com.study.demo.zk;

import java.io.IOException;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.Watcher.Event.KeeperState;

import org.apache.zookeeper.ZooKeeper;

//连接zk并监听事件

public class ZKDemo implements Watcher {

    private static final CountDownLatch cdl = new CountDownLatch(1);

    public static void main(String[] args) throws IOException {

        ZooKeeper zk = new ZooKeeper("192.168.152.130:2181", 5000, new ZKDemo());

        System.out.println(zk.getState());

        try {

            cdl.await();

        } catch (Exception e) {

            System.out.println("ZK Session established.");

        }

    }

    //监听到事件时进行处理

    public void process(WatchedEvent event) {

        System.out.println("Receive watched event:" + event);

        if (KeeperState.SyncConnected == event.getState()) {

            cdl.countDown();

        }

    }

}

输出结果：

CONNECTING
Receive watched event:WatchedEvent state:SyncConnected type:None path:null

2. 创建znode并监听事件

package com.study.demo.zk;

import java.io.IOException;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.KeeperException;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.Watcher.Event.KeeperState;

import org.apache.zookeeper.ZooDefs.Ids;

import org.apache.zookeeper.ZooKeeper;

//创建znode并监听事件

public class ZKOperateDemo implements Watcher {

    private static final CountDownLatch cdl = new CountDownLatch(1);

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {

        ZooKeeper zk = new ZooKeeper("192.168.152.130:2181", 5000, new ZKOperateDemo());

        cdl.await();

        String path1 = zk.create("/zk-test-", "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println("Success create path: " + path1);

        String path2 = zk.create("/zk-test-", "456".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);

        System.out.println("Success create path: " + path2);

    }

    //监听到事件时进行处理

    public void process(WatchedEvent event) {

        System.out.println("Receive watched event:" + event);

        if (KeeperState.SyncConnected == event.getState()) {

            cdl.countDown();

        }

    }

}

输出结果：

Receive watched event:WatchedEvent state:SyncConnected type:None path:null
Success create path: /zk-test-
Success create path: /zk-test-0000000011

3. 改变znode数据并监听事件

package com.study.demo.zk;

import java.io.IOException;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.KeeperException;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.Watcher.Event.EventType;

import org.apache.zookeeper.Watcher.Event.KeeperState;

import org.apache.zookeeper.ZooDefs.Ids;

import org.apache.zookeeper.ZooKeeper;

import org.apache.zookeeper.data.Stat;

//改变znode数据并监听事件

public class ZKDataDemo implements Watcher {

    private static final CountDownLatch cdl = new CountDownLatch(1);

    private static ZooKeeper zk = null;

    private static Stat stat = new Stat();

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {

        zk = new ZooKeeper("192.168.152.130:2181", 5000, new ZKDataDemo());

        cdl.await();

        zk.create("/zk-test", "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println(new String(zk.getData("/zk-test", true, stat)));

        zk.getData("/zk-test", true, stat);

        System.out.println(stat.getCzxid() + ", " + stat.getMzxid() + ", " + stat.getVersion());

        zk.setData("/zk-test", "123".getBytes(), -1);

        Thread.sleep(Integer.MAX_VALUE);

    }

    //监听到事件时进行处理

    public void process(WatchedEvent event) {

        if (KeeperState.SyncConnected == event.getState()) {

            if (EventType.None == event.getType() && null == event.getPath()) {

                cdl.countDown();

            } else if (event.getType() == EventType.NodeDataChanged) {

                try {

                    System.out.println(new String(zk.getData(event.getPath(), true, stat)));

                    System.out.println(stat.getCzxid() + ", " + stat.getMzxid() + ", " + stat.getVersion());

                } catch (Exception e) {

                }

            }

        }

    }

}

输出结果：

123
4294967354, 4294967354, 0
123
4294967354, 4294967355, 1

4. 改变子节点并监听事件

package com.study.demo.zk;

import java.io.IOException;

import java.util.List;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.KeeperException;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.Watcher.Event.EventType;

import org.apache.zookeeper.Watcher.Event.KeeperState;

import org.apache.zookeeper.ZooDefs.Ids;

import org.apache.zookeeper.ZooKeeper;

//改变子节点并监听事件

public class ZKChildrenDemo implements Watcher {

    private static final CountDownLatch cdl = new CountDownLatch(1);

    private static ZooKeeper zk = null;

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {

        zk = new ZooKeeper("192.168.152.130:2181", 5000, new ZKChildrenDemo());

        cdl.await();

        zk.create("/zk-test", "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

        zk.create("/zk-test/c1", "456".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        List<String> list = zk.getChildren("/zk-test", true);

        for (String str : list)

            System.out.println(str);

        zk.create("/zk-test/c2", "789".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        Thread.sleep(Integer.MAX_VALUE);

    }

    //监听到事件时进行处理

    public void process(WatchedEvent event) {

        if (KeeperState.SyncConnected == event.getState())

            if (EventType.None == event.getType() && null == event.getPath()) {

                cdl.countDown();

            } else if (event.getType() == EventType.NodeChildrenChanged) {

                try {

                    System.out.println("Child: " + zk.getChildren(event.getPath(), true));

                } catch (Exception e) {

                }

            }

    }

}

输出结果：

c1
Child: [c1, c2]

5. 异步调用并完成回调

package com.study.demo.zk;

import java.io.IOException;

import java.util.List;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.AsyncCallback;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.KeeperException;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.Watcher.Event.EventType;

import org.apache.zookeeper.Watcher.Event.KeeperState;

import org.apache.zookeeper.ZooDefs.Ids;

import org.apache.zookeeper.ZooKeeper;

import org.apache.zookeeper.data.Stat;

//异步调用并完成回调

class ChildrenCallback implements AsyncCallback.Children2Callback {

    public void processResult(int rc, String path, Object ctx, List<String> children, Stat stat) {

        System.out.println(

                "Child: " + rc + ", path: " + path + ", ctx: " + ctx + ", children: " + children + ", stat: " + stat);

    }

}

public class ZKChildrenAsyncDemo implements Watcher {

    private static final CountDownLatch cdl = new CountDownLatch(1);

    private static ZooKeeper zk = null;

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {

        zk = new ZooKeeper("192.168.152.130:2181", 5000, new ZKChildrenAsyncDemo());

        cdl.await();

        zk.create("/zk-test", "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

        zk.create("/zk-test/c1", "456".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        zk.getChildren("/zk-test", true, new ChildrenCallback(), "ok");

        Thread.sleep(Integer.MAX_VALUE);

    }

    //监听到事件时进行处理

    public void process(WatchedEvent event) {

        if (KeeperState.SyncConnected == event.getState())

            if (EventType.None == event.getType() && null == event.getPath()) {

                cdl.countDown();

            } else if (event.getType() == EventType.NodeChildrenChanged) {

                try {

                    System.out.println("Child: " + zk.getChildren(event.getPath(), true));

                } catch (Exception e) {

                }

            }

    }

}

输出结果：

Child: 0, path: /zk-test, ctx: ok, children: [c1], stat: 4294967369,4294967369,1535536716381,1535536716381,0,1,0,0,3,1,4294967370

6. 连接后创建回调

package com.study.demo.zk;

import java.io.IOException;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.AsyncCallback;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.KeeperException;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.Watcher.Event.KeeperState;

import org.apache.zookeeper.ZooDefs.Ids;

import org.apache.zookeeper.ZooKeeper;

//连接后创建回调

class IStringCallback implements AsyncCallback.StringCallback {

    public void processResult(int rc, String path, Object ctx, String name) {

        System.out.println("create path result: [" + rc + ", " + path + "," + ctx + ", real path name: " + name);

    }

}

public class ZKAsyncDemo implements Watcher {

    private static final CountDownLatch cdl = new CountDownLatch(1);

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {

        ZooKeeper zk = new ZooKeeper("192.168.152.130:2181", 5000, new ZKAsyncDemo());

        cdl.await();

        zk.create("/zk-test-", "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL, new IStringCallback(),

                new String("I am context"));

        zk.create("/zk-test-", "456".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL,

                new IStringCallback(), new String("I am context"));

        zk.create("/zk-test-", "789".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL,

                new IStringCallback(), new String("I am context"));

        Thread.sleep(Integer.MAX_VALUE);

    }

    //监听到事件时进行处理

    public void process(WatchedEvent event) {

        System.out.println("Receive watched event:" + event);

        if (KeeperState.SyncConnected == event.getState()) {

            cdl.countDown();

        }

    }

}

输出结果：

Receive watched event:WatchedEvent state:SyncConnected type:None path:null
create path result: [0, /zk-test-,I am context, real path name: /zk-test-
create path result: [-110, /zk-test-,I am context, real path name: null
create path result: [0, /zk-test-,I am context, real path name: /zk-test-0000000016

Chroot命名空间：
主要为了对业务进行隔离性

示例：
Zookeeper client=new Zookeeper(“192.168.56.101:2181/zk-client”, ........)
/zk-client就是Chroot命名空间。Chroot命名空间可以多级
后续的操作都只能在/zk-client及它的子节点下进行，由此进行了业务隔离

二、ZKClient

ZKClient的优点：

1）可以递归创建。在zookeeper命令行和zookeeper的原生API里面得先创建父节点才能创建子节点
2）可以递归删除。在zookeeper命令行和zookeeper的原生API里面得先删除子节点才能删除父节点
3）避免不存在的异常

准备工作：

首先在新建一个maven项目ZK-Demo,然后在pom.xml里面引入ZKClient的依赖

        <dependency>

            <groupId>com.101tec</groupId>

            <artifactId>zkclient</artifactId>

            <version>0.10</version>

        </dependency>

1. ZkClient递归创建顺序节点

package com.study.demo.client;

import org.I0Itec.zkclient.ZkClient;

/**

 *

* @Description: ZkClient递归创建顺序节点

* @author leeSmall

* @date 2018年9月2日

*

 */

public class CreateNodeDemo {

    public static void main(String[] args) {

        ZkClient client = new ZkClient("192.168.152.130:2181", 5000);

        String path = "/zk-client/c1";

        // 递归创建顺序节点 true：先创建父节点/zk-client

        client.createPersistent(path, true);

    }

}

创建成功：

Zookeeper系列三：Zookeeper客户端的使用（Zookeeper原生API如何进行调用、ZKClient、Curator）和Zookeeper会话

2. ZkClient获取数据并监听事件

package com.study.demo.client;

import org.I0Itec.zkclient.IZkDataListener;

import org.I0Itec.zkclient.ZkClient;

/**

*

* @Description: ZkClient获取数据

* @author leeSmall

* @date 2018年9月2日

*

*/

public class GetDataDemo {

    public static void main(String[] args) throws InterruptedException {

        String path = "/zk-client";

        ZkClient client = new ZkClient("192.168.152.130:2181", 5000);

        //创建临时节点

        client.createEphemeral(path, "123");

        //注册父节点数据改变的事件

        client.subscribeDataChanges(path, new IZkDataListener() {

            //父节点数据改变事件

            public void handleDataChange(String dataPath, Object data) throws Exception {

                System.out.println(dataPath + " changed: " + data);

            }

            //父节点数据删除事件

            public void handleDataDeleted(String dataPath) throws Exception {

                System.out.println(dataPath + " deleted");

            }

        });

        System.out.println(client.readData(path).toString());

        client.writeData(path, "456");

        Thread.sleep(1000);

        client.delete(path);

        //sleep的目的是为了更好的观察事件变化

        Thread.sleep(Integer.MAX_VALUE);

    }

}

输出结果：

123
/zk-client changed: 456
/zk-client deleted

3. ZkClient获取子节点数据并监听事件

package com.study.demo.client;

import java.util.List;

import org.I0Itec.zkclient.IZkChildListener;

import org.I0Itec.zkclient.ZkClient;

/**

*

* @Description: ZkClient获取子节点数据

* @author leeSmall

* @date 2018年9月2日

*

*/

public class GetChildrenDemo {

    public static void main(String[] args) throws InterruptedException {

        String path = "/zk-client";

        ZkClient client = new ZkClient("192.168.152.130:2181", 5000);

        //注册子节点数据改变的事件

        client.subscribeChildChanges(path, new IZkChildListener() {

            //子节点数据改变事件

            public void handleChildChange(String parentPath, List<String> currentChilds) throws Exception {

                System.out.println(parentPath + "的子发生变化: " + currentChilds);

            }

        });

        //创建顺序节点

        client.createPersistent(path);

        Thread.sleep(1000);

        //获取子节点数据 此时还没有创建获取不到

        System.out.println(client.getChildren(path));

        //在前面的父节点 /zk-client下创建子节点c1

        client.createPersistent(path + "/c1");

        Thread.sleep(1000);

        //删除子节点

        client.delete(path + "/c1");

        Thread.sleep(1000);

        //删除父节点

        client.delete(path);

        Thread.sleep(Integer.MAX_VALUE);

    }

}

输出结果：

/zk-client的子发生变化: []
[]
/zk-client的子发生变化: [c1]
/zk-client的子发生变化: []
/zk-client的子发生变化: null

三、Curator

curator是连接ZK应用最广泛的工具

原因如下：

1）zk应用场景（分布式锁，Master选举等等），curator包含了这些场景。
2）应用场景出现极端的情况下，curator考虑到处理了。

准备工作：

首先在新建一个maven项目ZK-Demo,然后在pom.xml里面引入curator的依赖

        <dependency>

            <groupId>org.apache.curator</groupId>

            <artifactId>curator-framework</artifactId>

            <version>4.0.0</version>

        </dependency>

        <dependency>

            <groupId>org.apache.curator</groupId>

            <artifactId>curator-recipes</artifactId>

            <version>4.0.0</version>

        </dependency>

1. curator创建连接session

package com.study.demo.curator;

import org.apache.curator.RetryPolicy;

import org.apache.curator.framework.CuratorFramework;

import org.apache.curator.framework.CuratorFrameworkFactory;

import org.apache.curator.retry.ExponentialBackoffRetry;

/**

*

* @Description: curator创建连接session

* @author leeSmall

* @date 2018年9月2日

*

*/

public class CreateSessionDemo {

    public static void main(String[] args) throws InterruptedException {

        RetryPolicy policy = new ExponentialBackoffRetry(1000, 3);

        CuratorFramework client = CuratorFrameworkFactory.builder().connectString("192.168.152.130:2181")

                .sessionTimeoutMs(5000).retryPolicy(policy).build();

        client.start();

        Thread.sleep(Integer.MAX_VALUE);

    }

}

这里介绍一种算法：Backoff退避算法

有这样一种场景，有多个请求，如果网络出现阻塞,每1分钟重试一次。
20：25 request1（block）
20：26 request2（block）
20：27 request3（block）
当网络通顺的时候，请求都累在一起来发送
20：28 request4（通顺）request2、3、4
那么前面的请求就没有意义了，所以就有了退避算法，按照指数间隔重试，比如第一次1分钟，第二次2分钟......随着时间的推移，重试间隔越长。

2. curator递归创建顺序节点

package com.study.demo.curator;

import org.apache.curator.framework.CuratorFramework;

import org.apache.curator.framework.CuratorFrameworkFactory;

import org.apache.curator.retry.ExponentialBackoffRetry;

import org.apache.zookeeper.CreateMode;

/**

*

* @Description: curator递归创建顺序节点

* @author leeSmall

* @date 2018年9月2日

*

*/

public class CreateNodeDemo {

    public static void main(String[] args) throws Exception {

        String path = "/zk-curator/c1";

        CuratorFramework client = CuratorFrameworkFactory.builder().connectString("192.168.152.130:2181")

                .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();

        client.start();

        client.create().creatingParentsIfNeeded().withMode(CreateMode.PERSISTENT).forPath(path, "test".getBytes());

    }

}

创建成功：

Zookeeper系列三：Zookeeper客户端的使用（Zookeeper原生API如何进行调用、ZKClient、Curator）和Zookeeper会话

3. curator异步创建临时节点

package com.study.demo.curator;

import java.util.concurrent.CountDownLatch;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import org.apache.curator.framework.CuratorFramework;

import org.apache.curator.framework.CuratorFrameworkFactory;

import org.apache.curator.framework.api.BackgroundCallback;

import org.apache.curator.framework.api.CuratorEvent;

import org.apache.curator.retry.ExponentialBackoffRetry;

import org.apache.zookeeper.CreateMode;

/**

*

* @Description: curator异步创建临时节点

* @author leeSmall

* @date 2018年9月2日

*

*/

public class CreateNodeAsyncDemo {

    static CountDownLatch cdl = new CountDownLatch(2);

    static ExecutorService es = Executors.newFixedThreadPool(2);

    public static void main(String[] args) throws Exception {

        String path = "/zk-curator";

        CuratorFramework client = CuratorFrameworkFactory.builder().connectString("192.168.152.130:2181")

                .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();

        client.start();

        //创建临时节点

        client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).inBackground(new BackgroundCallback() {

            //回调事件处理

            public void processResult(CuratorFramework client, CuratorEvent event) throws Exception {

                System.out.println("event code: " + event.getResultCode() + ", type: " + event.getType());

                cdl.countDown();

            }

        }, es).forPath(path, "test".getBytes());

        //创建临时节点

        client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).inBackground(new BackgroundCallback() {

            public void processResult(CuratorFramework client, CuratorEvent event) throws Exception {

                System.out.println("event code: " + event.getResultCode() + ", type: " + event.getType());

                cdl.countDown();

            }

        }).forPath(path, "test".getBytes());

        cdl.await();

        es.shutdown();

    }

}

输出结果：

event code: 0, type: CREATE
event code: -110, type: CREATE

4. curator更新节点数据

package com.study.demo.curator;

import org.apache.curator.framework.CuratorFramework;

import org.apache.curator.framework.CuratorFrameworkFactory;

import org.apache.curator.retry.ExponentialBackoffRetry;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.data.Stat;

/**

*

* @Description: curator更新节点数据

* @author leeSmall

* @date 2018年9月2日

*

*/

public class UpdateDataDemo {

    public static void main(String[] args) throws Exception {

        String path = "/zk-curator/c1";

        CuratorFramework client = CuratorFrameworkFactory.builder().connectString("192.168.152.130:2181")

                .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();

        client.start();

        client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "test".getBytes());

        Stat stat = new Stat();

        client.getData().storingStatIn(stat).forPath(path);

        System.out.println("Current data: " + stat.getVersion());

        System.out.println("Update data: "

                + client.setData().withVersion(stat.getVersion()).forPath(path, "some".getBytes()).getVersion());

    }

}

输出结果：

Current data: 0
Update data: 1

5. curator删除节点数据

package com.study.demo.curator;

import org.apache.curator.framework.CuratorFramework;

import org.apache.curator.framework.CuratorFrameworkFactory;

import org.apache.curator.retry.ExponentialBackoffRetry;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.data.Stat;

/**

*

* @Description: curator删除节点数据

* @author leeSmall

* @date 2018年9月2日

*

*/

public class DeleteNodeDemo {

    public static void main(String[] args) throws Exception {

        String path = "/zk-curator/c1";

        CuratorFramework client = CuratorFrameworkFactory.builder().connectString("192.168.152.130:2181")

                .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();

        client.start();

        client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "test".getBytes());

        Stat stat = new Stat();

        client.getData().storingStatIn(stat).forPath(path);

        client.delete().deletingChildrenIfNeeded().withVersion(stat.getVersion()).forPath(path);

    }

}

6. curator事件监听

package com.study.demo.curator;

import org.apache.curator.framework.CuratorFramework;

import org.apache.curator.framework.CuratorFrameworkFactory;

import org.apache.curator.framework.recipes.cache.NodeCache;

import org.apache.curator.framework.recipes.cache.NodeCacheListener;

import org.apache.curator.retry.ExponentialBackoffRetry;

import org.apache.zookeeper.CreateMode;

/**

*

* @Description: curator事件监听

* @author leeSmall

* @date 2018年9月2日

*

*/

public class NodeCacheDemo {

    public static void main(String[] args) throws Exception {

        String path = "/zk-curator/nodecache";

        CuratorFramework client = CuratorFrameworkFactory.builder().connectString("192.168.152.130:2181")

                .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();

        client.start();

        client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "test".getBytes());

        final NodeCache nc = new NodeCache(client, path, false);

        nc.start();

        //通过回调函数监听事件

        nc.getListenable().addListener(new NodeCacheListener() {

            public void nodeChanged() throws Exception {

                System.out.println("update--current data: " + new String(nc.getCurrentData().getData()));

            }

        });

        client.setData().forPath(path, "test123".getBytes());

        Thread.sleep(1000);

        client.delete().deletingChildrenIfNeeded().forPath(path);

        Thread.sleep(5000);

        nc.close();

    }

}

输出结果：

update--current data: test123

Curator事件监听：

NodeCache：节点处理监听（会使用缓存）。回调接口NodeCacheListener

PathChildrenCache：子节点缓存，处理子节点变化。回调接口PathChildrenCacheListener

TreeCache：NodeCache和PathChildrenCache的结合体。回调接口TreeCacheListener

四、zookeeper会话

1. zookeeper连接的几种状态

CONNECTING 正在连接
CONNECTED 已经连接
RECONNECTING 正在重新连接
RECONNECTED 重新连接上
CLOSE 会话关闭

2. session

2.1 session主要由几个类控制：

SessionTracker, LearnerSessionTracker, SessionTrackerImpl

Zookeeper系列三：Zookeeper客户端的使用（Zookeeper原生API如何进行调用、ZKClient、Curator）和Zookeeper会话

session初始化的方法：

org.apache.zookeeper.server.SessionTrackerImpl.initializeNextSession(long)

public static long initializeNextSession(long id) {

        long nextSid = 0;

        nextSid = (System.currentTimeMillis() << 24) >>> 8;

        nextSid =  nextSid | (id <<56);

        return nextSid;

    }

说明：

SessionID的分配（初始化）函数，策略如下：
1）取时间，并且左移24位得到的结果再右移8位（高8位，低16位都是0）
2）sid拿出来进行左移56位
3）和第一步的结果做或运算

2.2 Session分桶（zookeeper的一个特性）

按照Session会话过期时间进行分区块保存。
这样设计的好处：可以快速清理过期的session

2.3 session激活过程：

1）检测会话是否过期
2）计算会话下一次超时时间
3）定位会话的所在区块
4）迁移会话

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