1  创建节点

创建节点有异步和同步两种方式。无论是异步或者同步，Zookeeper都不支持递归调用，即无法在父节点不存在的情况下创建一个子节点，如在/zk-ephemeral节点不存在的情况下创建/zk-ephemeral/ch1节点；并且如果一个节点已经存在，那么创建同名节点时，会抛出NodeExistsException异常。

① 同步方式

package com.hust.grid.leesf.examples;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.CreateMode;

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;

public class Zookeeper_Create_API_Sync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

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

        ZooKeeper zookeeper = new ZooKeeper("127.0.0.1:2181", 5000, new Zookeeper_Create_API_Sync_Usage());

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

        connectedSemaphore.await();

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

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

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

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

    }

    public void process(WatchedEvent event) {

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

            connectedSemaphore.countDown();

        }

    }

} 

运行结果如下　　

CONNECTING

Success create znode: /zk-test-ephemeral-

Success create znode: /zk-test-ephemeral-0000000043

结果表明已经成功创建了临时节点和临时顺序节点，在创建顺序节点时，系统会在后面自动增加一串数字。

② 异步方式

使用异步方式于同步方式的区别在于节点的创建过程（包括网络通信和服务端的节点创建过程）是异步的，在同步接口调用过程中，开发者需要关注接口抛出异常的可能，但是在异步接口中，接口本身不会抛出异常，所有异常都会在回调函数中通过Result Code来体现。

package com.hust.grid.leesf.examples;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.AsyncCallback;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.ZooKeeper;

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

import org.apache.zookeeper.ZooDefs.Ids;

public class Zookeeper_Create_API_ASync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

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

        ZooKeeper zookeeper = new ZooKeeper("127.0.0.1:2181", 5000, new Zookeeper_Create_API_ASync_Usage());

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

        connectedSemaphore.await();

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

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

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

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

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

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

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

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

            connectedSemaphore.countDown();

        }

    }

}

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);

    }

} 

运行结果如下　

CONNECTING

Create path result: [0, /zk-test-ephemeral-, I am context. , real path name: /zk-test-ephemeral-

Create path result: [-110, /zk-test-ephemeral-, I am context. , real path name: null

Create path result: [0, /zk-test-ephemeral-, I am context. , real path name: /zk-test-ephemeral-0000000045

结果表明已经成功使用异步方式创建了相应节点。

2 删除节点　

只允许删除叶子节点，即一个节点如果有子节点，那么该节点将无法直接删除，必须先删掉其所有子节点。同样也有同步和异步两种方式。　

① 同步方式

package com.hust.grid.leesf.examples;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.CreateMode;

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;

public class Delete_API_Sync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private static ZooKeeper zk;

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

        String path = "/zk-book";

        zk = new ZooKeeper("127.0.0.1:2181", 5000, new Delete_API_Sync_Usage());

        connectedSemaphore.await();

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

        System.out.println("success create znode: " + path);

        zk.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

        System.out.println("success create znode: " + path + "/c1");

        try {

            zk.delete(path, -1);

        } catch (Exception e) {

            System.out.println("fail to delete znode: " + path);

        }

        zk.delete(path + "/c1", -1);

        System.out.println("success delete znode: " + path + "/c1");

        zk.delete(path, -1);

        System.out.println("success delete znode: " + path);

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

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

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

                connectedSemaphore.countDown();

            }

        }

    }

} 

运行结果如下　

success create znode: /zk-book

success create znode: /zk-book/c1

fail to delete znode: /zk-book

success delete znode: /zk-book/c1

success delete znode: /zk-book

结果表明若节点有子节点，则无法将其删除，必须先删除其所有子节点。

② 异步方式

package com.hust.grid.leesf.examples;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.AsyncCallback;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.ZooKeeper;

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

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

import org.apache.zookeeper.ZooDefs.Ids;

public class Delete_API_ASync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private static ZooKeeper zk;

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

        String path = "/zk-book";

        zk = new ZooKeeper("127.0.0.1:2181", 5000, new Delete_API_ASync_Usage());

        connectedSemaphore.await();

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

        System.out.println("success create znode: " + path);

        zk.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

        System.out.println("success create znode: " + path + "/c1");

        zk.delete(path, -1, new IVoidCallback(), null);

        zk.delete(path + "/c1", -1, new IVoidCallback(), null);

        zk.delete(path, -1, new IVoidCallback(), null);        

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

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

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

                connectedSemaphore.countDown();

            }

        }

    }

}

class IVoidCallback implements AsyncCallback.VoidCallback {

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

        System.out.println(rc + ", " + path + ", " + ctx);

    }

} 

运行结果如下　　

success create znode: /zk-book

success create znode: /zk-book/c1

-111, /zk-book, null

0, /zk-book/c1, null

0, /zk-book, null

结果结果表明第一次删除/zk-book的时异常，ResultCode为-111。

3 子节点获取

读取节点的子节点列表，同样可以使用同步和异步的方式进行操作。

① 同步方式

package com.hust.grid.leesf.examples;

import java.util.List;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.ZooKeeper;

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

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

import org.apache.zookeeper.ZooDefs.Ids;

public class Zookeeper_GetChildren_API_Sync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private static ZooKeeper zk = null;

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

        String path = "/zk-book-1";

        zk = new ZooKeeper("127.0.0.1:2181", 5000, new Zookeeper_GetChildren_API_Sync_Usage());

        connectedSemaphore.await();

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

        System.out.println("success create znode: " + path);

        zk.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println("success create znode: " + path + "/c1");

        List<String> childrenList = zk.getChildren(path, true);

        System.out.println(childrenList);

        zk.create(path + "/c2", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println("success create znode: " + path + "/c2");

        Thread.sleep(1000);

        zk.create(path + "/c3", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println("success create znode: " + path + "/c3");

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

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

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

                connectedSemaphore.countDown();

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

                try {

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

                } catch (Exception e) {

                }

            }

        }

    }

} 

运行结果如下　

success create znode: /zk-book-1

success create znode: /zk-book-1/c1

[c1]

success create znode: /zk-book-1/c2

ReGet Child:[c1, c2]

success create znode: /zk-book-1/c3

ReGet Child:[c3, c1, c2]

值得注意的是，Watcher通知是一次性的，即一旦触发一次通知后，该Watcher就失效了，因此客户端需要反复注册Watcher，即程序中在process里面又注册了Watcher，否则，将无法获取c3节点的创建而导致子节点变化的事件。

② 异步方式

package com.hust.grid.leesf.examples;

import java.util.List;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.AsyncCallback;

import org.apache.zookeeper.CreateMode;

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;

public class Zookeeper_GetChildren_API_ASync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private static ZooKeeper zk = null;

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

        String path = "/zk-book";

        zk = new ZooKeeper("127.0.0.1:2181", 5000, new Zookeeper_GetChildren_API_ASync_Usage());

        connectedSemaphore.await();

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

        System.out.println("success create znode: " + path);

        zk.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println("success create znode: " + path + "/c1");

        zk.getChildren(path, true, new IChildren2Callback(), null);

        zk.create(path + "/c2", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println("success create znode: " + path + "/c2");

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

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

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

                connectedSemaphore.countDown();

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

                try {

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

                } catch (Exception e) {

                }

            }

        }

    }

}

class IChildren2Callback implements AsyncCallback.Children2Callback {

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

        System.out.println("Get Children znode result: [response code: " + rc + ", param path: " + path + ", ctx: "

                + ctx + ", children list: " + children + ", stat: " + stat);

    }

} 

运行结果如下　　

success create znode: /zk-book

success create znode: /zk-book/c1

Get Children znode result: [response code: 0, param path: /zk-book, ctx: null, children list: [c1], stat: 2901,2901,1478226062843,1478226062843,0,1,0,0,0,1,2902

success create znode: /zk-book/c2

ReGet Child:[c1, c2]

结果表示通过异步的方式可以获取子节点信息。

4 数据节点获取

对于节点的数据获取，同样存在同步和异步两种方式。

① 同步方式

package com.hust.grid.leesf.examples;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.CreateMode;

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;

public class GetData_API_Sync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private static ZooKeeper zk = null;

    private static Stat stat = new Stat();

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

        String path = "/zk-book";

        zk = new ZooKeeper("127.0.0.1:2181", 5000,

                new GetData_API_Sync_Usage());

        connectedSemaphore.await();

        zk.create(path, "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println("success create znode: " + path);

        System.out.println("the data of znode " + path + " is : " + new String(zk.getData(path, true, stat)));

        System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " + stat.getVersion());

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

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

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

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

                connectedSemaphore.countDown();

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

                try {

                    System.out.println("the data of znode " + event.getPath() + " is : " + new String(zk.getData(event.getPath(), true, stat)));

                    System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " + stat.getVersion());

                } catch (Exception e) {

                }

            }

        }

    }

} 

运行结果如下　　

success create znode: /zk-book

the data of /zk-book is : 123

czxID: 2924, mzxID: 2924, version: 0

the data of /zk-book is : 123

czxID: 2924, mzxID: 2925, version: 1

结果表明可以使用getData函数获取节点的数据。

② 异步方式

package com.hust.grid.leesf.examples;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.AsyncCallback;

import org.apache.zookeeper.CreateMode;

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;

public class GetData_API_ASync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private static ZooKeeper zk;

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

        String path = "/zk-book";

        zk = new ZooKeeper("127.0.0.1:2181", 5000,

                new GetData_API_ASync_Usage());

        connectedSemaphore.await();

        zk.create(path, "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println("success create znode: " + path);

        zk.getData(path, true, new IDataCallback(), null);

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

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

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

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

                connectedSemaphore.countDown();

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

                try {

                    zk.getData(event.getPath(), true, new IDataCallback(), null);

                } catch (Exception e) {

                }

            }

        }

    }

}

class IDataCallback implements AsyncCallback.DataCallback {

    public void processResult(int rc, String path, Object ctx, byte[] data, Stat stat) {

        System.out.println("rc: " + rc + ", path: " + path + ", data: " + new String(data));

        System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " + stat.getVersion());

    }

} 

运行结果如下　　

success create znode: /zk-book

rc: 0, path: /zk-book, data: 123

czxID: 2932, mzxID: 2932, version: 0

rc: 0, path: /zk-book, data: 123

czxID: 2932, mzxID: 2933, version: 1

结果表明采用异步方式同样可方便获取节点的数据。

5 更新数据

在更新数据时，setData方法存在一个version参数，其用于指定节点的数据版本，表明本次更新操作是针对指定的数据版本进行的，但是，在getData方法中，并没有提供根据指定数据版本来获取数据的接口，那么，这里为何要指定数据更新版本呢，这里方便理解，可以等效于CAS（compare and swap），对于值V，每次更新之前都会比较其值是否是预期值A，只有符合预期，才会将V原子化地更新到新值B。Zookeeper的setData接口中的version参数可以对应预期值，表明是针对哪个数据版本进行更新，假如一个客户端试图进行更新操作，它会携带上次获取到的version值进行更新，而如果这段时间内，Zookeeper服务器上该节点的数据已经被其他客户端更新，那么其数据版本也会相应更新，而客户端携带的version将无法匹配，无法更新成功，因此可以有效地避免分布式更新的并发问题。

① 同步方式

package com.hust.grid.leesf.examples;

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;

public class SetData_API_Sync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private static ZooKeeper zk;

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

        String path = "/zk-book";

        zk = new ZooKeeper("127.0.0.1:2181", 5000, new SetData_API_Sync_Usage());

        connectedSemaphore.await();

        zk.create(path, "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println("success create znode: " + path);

        zk.getData(path, true, null);

        Stat stat = zk.setData(path, "456".getBytes(), -1);

        System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " + stat.getVersion());

        Stat stat2 = zk.setData(path, "456".getBytes(), stat.getVersion());

        System.out.println("czxID: " + stat2.getCzxid() + ", mzxID: " + stat2.getMzxid() + ", version: " + stat2.getVersion());

        try {

            zk.setData(path, "456".getBytes(), stat.getVersion());

        } catch (KeeperException e) {

            System.out.println("Error: " + e.code() + "," + e.getMessage());

        }

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

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

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

                connectedSemaphore.countDown();

            }

        }

    }

} 

运行结果如下　

success create znode: /zk-book

czxID: 2936, mzxID: 2937, version: 1

czxID: 2936, mzxID: 2938, version: 2

Error: BADVERSION,KeeperErrorCode = BadVersion for /zk-book

结果表明由于携带的数据版本不正确，而无法成功更新节点。其中，setData中的version参数设置-1含义为客户端需要基于数据的最新版本进行更新操作。

② 异步方式

package com.hust.grid.leesf.examples;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.AsyncCallback;

import org.apache.zookeeper.CreateMode;

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;

public class SetData_API_ASync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private static ZooKeeper zk;

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

        String path = "/zk-book";

        zk = new ZooKeeper("127.0.0.1:2181", 5000, new SetData_API_ASync_Usage());

        connectedSemaphore.await();

        zk.create(path, "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println("success create znode: " + path);

        zk.setData(path, "456".getBytes(), -1, new IStatCallback(), null);

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

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

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

                connectedSemaphore.countDown();

            }

        }

    }

}

class IStatCallback implements AsyncCallback.StatCallback {

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

        System.out.println("rc: " + rc + ", path: " + path + ", stat: " + stat);

    }

} 

运行结果如下　　

success create znode: /zk-book

rc: 0, path: /zk-book, stat: 2942,2943,1478228414526,1478228414545,1,0,0,96876700808708136,3,0,2942

rc（ResultCode）为0，表明成功更新节点数据。

6 检测节点是否存在

在调用接口时注册Watcher的话，还可以对节点是否存在进行监听，一旦节点被创建、被删除、数据更新，都会通知客户端。

① 同步方式

package com.hust.grid.leesf.examples;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.CreateMode;

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;

public class Exist_API_Sync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private static ZooKeeper zk;

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

        String path = "/zk-book";

        zk = new ZooKeeper("127.0.0.1:2181", 5000, //

                new Exist_API_Sync_Usage());

        connectedSemaphore.await();

        zk.exists(path, true);

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

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

        zk.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

        System.out.println("success create znode: " + path + "/c1");

        zk.delete(path + "/c1", -1);

        zk.delete(path, -1);

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

        try {

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

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

                    connectedSemaphore.countDown();

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

                    System.out.println("success create znode: " + event.getPath());

                    zk.exists(event.getPath(), true);

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

                    System.out.println("success delete znode: " + event.getPath());

                    zk.exists(event.getPath(), true);

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

                    System.out.println("data changed of znode: " + event.getPath());

                    zk.exists(event.getPath(), true);

                }

            }

        } catch (Exception e) {

        }

    }

} 

运行结果如下　

success create znode: /zk-book

data changed of znode: /zk-book

success create znode: /zk-book/c1

success delete znode: /zk-book

结果表明：

　　· 无论节点是否存在，都可以通过exists接口注册Watcher。

　　· 注册的Watcher，对节点创建、删除、数据更新事件进行监听。

　　· 对于指定节点的子节点的各种变化，不会通知客户端。

② 异步方式

package com.hust.grid.leesf.examples;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.AsyncCallback;

import org.apache.zookeeper.CreateMode;

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;

public class Exist_API_ASync_Usage implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private static ZooKeeper zk;

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

        String path = "/zk-book";

        zk = new ZooKeeper("127.0.0.1:2181", 5000,

                new Exist_API_ASync_Usage());

        connectedSemaphore.await();

        zk.exists(path, true, new IIStatCallback(), null);

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

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

        zk.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

        System.out.println("success create znode: " + path + "/c1");

        zk.delete(path + "/c1", -1);

        zk.delete(path, -1);

        Thread.sleep(Integer.MAX_VALUE);

    }

    public void process(WatchedEvent event) {

        try {

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

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

                    connectedSemaphore.countDown();

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

                    System.out.println("success create znode: " + event.getPath());

                    zk.exists(event.getPath(), true, new IIStatCallback(), null);

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

                    System.out.println("success delete znode: " + event.getPath());

                    zk.exists(event.getPath(), true, new IIStatCallback(), null);

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

                    System.out.println("data changed of znode: " + event.getPath());

                    zk.exists(event.getPath(), true, new IIStatCallback(), null);

                }

            }

        } catch (Exception e) {

        }

    }

}

class IIStatCallback implements AsyncCallback.StatCallback {

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

        System.out.println("rc: " + rc + ", path: " + path + ", stat: " + stat);

    }

} 

运行结果如下

rc: -101, path: /zk-book, stat: null

success create znode: /zk-book

rc: 0, path: /zk-book, stat: 2974,2974,1478229717889,1478229717889,0,0,0,0,0,0,2974

data changed of znode: /zk-book

rc: 0, path: /zk-book, stat: 2974,2975,1478229717889,1478229717922,1,0,0,0,3,0,2974

success create znode: /zk-book/c1

success delete znode: /zk-book

rc: -101, path: /zk-book, stat: null

结果表明当节点不存在时，其rc（ResultCode）为-101。

7 权限控制

通过设置Zookeeper服务器上数据节点的ACL控制，就可以对其客户端对该数据节点的访问权限：如果符合ACL控制，则可以进行访问，否则无法访问。

① 使用无权限信息的Zookeeper会话访问含权限信息的数据节点

package com.hust.grid.leesf.examples;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.ZooDefs.Ids;

import org.apache.zookeeper.ZooKeeper;

public class AuthSample_Get {

    final static String PATH = "/zk-book-auth_test";

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

        ZooKeeper zookeeper1 = new ZooKeeper("127.0.0.1:2181", 5000, null);

        zookeeper1.addAuthInfo("digest", "foo:true".getBytes());

        zookeeper1.create(PATH, "init".getBytes(), Ids.CREATOR_ALL_ACL, CreateMode.EPHEMERAL);

        System.out.println("success create znode: " + PATH);

        ZooKeeper zookeeper2 = new ZooKeeper("127.0.0.1:2181", 5000, null);

        zookeeper2.getData(PATH, false, null);

    }

} 

运行结果如下　

success create znode: /zk-book-auth_test

Exception in thread "main" org.apache.zookeeper.KeeperException$NoAuthException: KeeperErrorCode = NoAuth for /zk-book-auth_test

    at org.apache.zookeeper.KeeperException.create(KeeperException.java:113)

    at org.apache.zookeeper.KeeperException.create(KeeperException.java:51)

    at org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1155)

    at org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1184)

    at com.hust.grid.leesf.examples.AuthSample_Get.main(AuthSample_Get.java:17)

表示权限不够，不能进行操作。

② 删除带权限控制的节点

package com.hust.grid.leesf.examples;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.ZooDefs.Ids;

import org.apache.zookeeper.ZooKeeper;

public class AuthSample_Delete {

    final static String PATH = "/zk-book-auth_test";

    final static String PATH2 = "/zk-book-auth_test/child";

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

        ZooKeeper zookeeper1 = new ZooKeeper("127.0.0.1:2181", 5000, null);

        zookeeper1.addAuthInfo("digest", "foo:true".getBytes());

        zookeeper1.create(PATH, "init".getBytes(), Ids.CREATOR_ALL_ACL, CreateMode.PERSISTENT);

        zookeeper1.create(PATH2, "init".getBytes(), Ids.CREATOR_ALL_ACL, CreateMode.EPHEMERAL);

        try {

            ZooKeeper zookeeper2 = new ZooKeeper("127.0.0.1:2181", 5000, null);

            zookeeper2.delete(PATH2, -1);

        } catch (Exception e) {

            System.out.println("fail to delete: " + e.getMessage());

        }

        ZooKeeper zookeeper3 = new ZooKeeper("127.0.0.1:2181", 5000, null);

        zookeeper3.addAuthInfo("digest", "foo:true".getBytes());

        zookeeper3.delete(PATH2, -1);

        System.out.println("success delete znode: " + PATH2);

        ZooKeeper zookeeper4 = new ZooKeeper("127.00.1:2181", 5000, null);

        zookeeper4.delete(PATH, -1);

        System.out.println("success delete znode: " + PATH);

    }

} 

运行结果如下　　

fail to delete: KeeperErrorCode = NoAuth for /zk-book-auth_test/child

success delete znode: /zk-book-auth_test/child

success delete znode: /zk-book-auth_test

结果表明若没有权限，则无法删除节点。

参考资料

http://www.cnblogs.com/leesf456/p/6028416.html

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