Zookeeper服务框架之Java API的使用(三)
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一、开发环境配置
第一：打开Zookeeper服务端，参考之前的博客。
第二：配置开发环境环境可以有两种方式：
① 直接下载相关的依赖Jar包，然后在IDE中添加依赖。
② 建立maven项目，使用maven进行依赖管理。
现在开发步骤(① 手动添加依赖至IDE)如下：
步骤一：点击http://hadoop.apache.org/zookeeper/下载对应版本的Jar包，包括（jar、javadoc.jar、sources.jar），笔者对应下载的Zookeeper3.4.9版本。
步骤二：打开IDE（笔者使用eclispe），新建名为zookeeperApp1的java项目，并添加相应的jar包。
步骤三：新建包、Java类进行测试。
package com.npf.test;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;public class ZookeeperApp1Test { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static void main(String[] args) throws Exception { ZooKeeper zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher(){ @Override public void process(WatchedEvent event) { System.out.println("Receive watched event : " + event); if (KeeperState.SyncConnected == event.getState()) { connectedSemaphore.countDown(); } }} ); System.out.println(zookeeper.getState()); try { connectedSemaphore.await(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Zookeeper session established"); }}运行结果如下:
现在开发步骤(② 使用maven管理依赖)如下：
步骤一：新建maven项目.
步骤二：配置pom.xml文件如下:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.npf</groupId> <artifactId>zookeeperApp2</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>zookeeperApp2</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <scope>test</scope> </dependency> <dependency> <groupId>org.apache.zookeeper</groupId> <artifactId>zookeeper</artifactId> <version>3.4.9</version> </dependency> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.16</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>1.6.1</version> </dependency> </dependencies> <profiles> <profile> <id>jdk-1.7</id> <activation> <activeByDefault>true</activeByDefault> <jdk>1.7</jdk> </activation> <properties> <maven.compiler.source>1.7</maven.compiler.source> <maven.compiler.target>1.7</maven.compiler.target> <maven.compiler.compilerVersion>1.7</maven.compiler.compilerVersion> </properties> </profile> </profiles> </project>
步骤三：新建java类进行测试:
package com.npf.test;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;public class ZookeeperApp2Test { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static void main(String[] args) throws Exception { ZooKeeper zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher(){ @Override public void process(WatchedEvent event) { System.out.println("Receive watched event : " + event); if (KeeperState.SyncConnected == event.getState()) { connectedSemaphore.countDown(); } }} ); System.out.println(zookeeper.getState()); try { connectedSemaphore.await(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Zookeeper session established"); }}运行结果如下:
二、操作示例
3.1 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.npf.test;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 ZookeeperCreateNodeAPITest { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static void main(String[] args) throws Exception { ZooKeeper zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher(){ @Override public void process(WatchedEvent event) { if (KeeperState.SyncConnected == event.getState()) { connectedSemaphore.countDown(); } }} ); System.out.println(zookeeper.getState()); connectedSemaphore.await(); String path1 = zookeeper.create("/zk-test-ephemeral-", "datatest".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); System.out.println("Success create znode: " + path1); String path2 = zookeeper.create("/zk-test-ephemeral-", "datatest".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL); System.out.println("Success create znode: " + path2); }}运行结果如下：
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
使用异步方式与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.npf.test;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.KeeperState;import org.apache.zookeeper.ZooDefs.Ids;import org.apache.zookeeper.ZooKeeper;public class ZookeeperCreateNodeAPITest2 { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static void main(String[] args) throws Exception { ZooKeeper zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override public void process(WatchedEvent event) { if (KeeperState.SyncConnected == event.getState()) { connectedSemaphore.countDown(); } } }); System.out.println(zookeeper.getState()); connectedSemaphore.await(); zookeeper.create("/zk-test-ephemeral-", "datatest".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL, new IStringCallback(), "I am context. "); zookeeper.create("/zk-test-ephemeral-", "datatest".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL, new IStringCallback(), "I am context. "); zookeeper.create("/zk-test-ephemeral-", "datatest".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL, new IStringCallback(), "I am context. "); Thread.sleep(Integer.MAX_VALUE); }}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：
结果表明已经成功使用异步方式创建了相应节点。
3.2 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.npf.test;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 ZookeeperDeleteNodeAPITest { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static void main(String[] args) throws Exception { String path = "/zk-book"; ZooKeeper zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override public void process(WatchedEvent event) { if (KeeperState.SyncConnected == event.getState()) { if (EventType.None == event.getType() && null == event.getPath()) { connectedSemaphore.countDown(); } } } }); connectedSemaphore.await(); zookeeper.create(path, "testdata".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); System.out.println("success create znode: " + path); zookeeper.create(path + "/c1", "testdata".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); System.out.println("success create znode: " + path + "/c1"); try { zookeeper.delete(path, -1); } catch (Exception e) { System.out.println("fail to delete znode: " + path); } zookeeper.delete(path + "/c1", -1); System.out.println("success delete znode: " + path + "/c1"); zookeeper.delete(path, -1); System.out.println("success delete znode: " + path); Thread.sleep(Integer.MAX_VALUE); }}运行结果如下：
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.npf.test;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;public class ZookeeperDeleteNodeAPITest2 { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static void main(String[] args) throws Exception { String path = "/zk-book"; ZooKeeper zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override public void process(WatchedEvent event) { if (KeeperState.SyncConnected == event.getState()) { if (EventType.None == event.getType() && null == event.getPath()) { connectedSemaphore.countDown(); } } } }); connectedSemaphore.await(); zookeeper.create(path, "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); System.out.println("success create znode: " + path); zookeeper.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); System.out.println("success create znode: " + path + "/c1"); zookeeper.delete(path, -1, new IVoidCallback(), null); zookeeper.delete(path + "/c1", -1, new IVoidCallback(), null); zookeeper.delete(path, -1, new IVoidCallback(), null); Thread.sleep(Integer.MAX_VALUE); }}class IVoidCallback implements AsyncCallback.VoidCallback { @Override public void processResult(int rc, String path, Object ctx) { System.out.println(rc + ", " + path + ", " + ctx); }}运行结果如下:
结果结果表明第一次删除/zk-book的时异常，ResultCode为-111。
3.3 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.npf.test;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.Watcher.Event.EventType;import org.apache.zookeeper.Watcher.Event.KeeperState;import org.apache.zookeeper.ZooDefs.Ids;import org.apache.zookeeper.ZooKeeper;public class ZookeeperGetNodeAPITest { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static ZooKeeper zookeeper = null; public static void main(String[] args) throws Exception { String path = "/zk-book-1"; zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override 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:" + zookeeper.getChildren(event.getPath(), true)); } catch (Exception e) { } } } } }); connectedSemaphore.await(); zookeeper.create(path, "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); System.out.println("success create znode: " + path); zookeeper.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); System.out.println("success create znode: " + path + "/c1"); List<String> childrenList = zookeeper.getChildren(path, true); System.out.println(childrenList); zookeeper.create(path + "/c2", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); System.out.println("success create znode: " + path + "/c2"); Thread.sleep(1000); zookeeper.create(path + "/c3", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); System.out.println("success create znode: " + path + "/c3"); Thread.sleep(Integer.MAX_VALUE); }}运行结果如下:
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.npf.test;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 ZookeeperGetNodeAPITest2 { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static ZooKeeper zookeeper = null; public static void main(String[] args) throws Exception { String path = "/zk-book-2"; zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override 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:" + zookeeper.getChildren(event.getPath(), true)); } catch (Exception e) { } } } } }); connectedSemaphore.await(); zookeeper.create(path, "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); System.out.println("success create znode: " + path); zookeeper.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); System.out.println("success create znode: " + path + "/c1"); zookeeper.getChildren(path, true, new IChildren2Callback(), null); zookeeper.create(path + "/c2", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); System.out.println("success create znode: " + path + "/c2"); Thread.sleep(Integer.MAX_VALUE); }}class IChildren2Callback implements AsyncCallback.Children2Callback { @Override 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:
结果表示通过异步的方式可以获取子节点信息。
3.4 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.npf.test;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 ZookeeperGetDataAPITest { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static ZooKeeper zookeeper = null; private static Stat stat = new Stat(); public static void main(String[] args) throws Exception { String path = "/zk-book-4"; zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override 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(zookeeper.getData( event.getPath(), true, stat))); System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " + stat.getVersion()); } catch (Exception e) { } } } } }); connectedSemaphore.await(); zookeeper.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(zookeeper.getData(path, true, stat))); System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " + stat.getVersion()); zookeeper.setData(path, "1234".getBytes(), -1); Thread.sleep(Integer.MAX_VALUE); }}运行结果如下:
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.npf.test;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 ZookeeperGetDataAPITest2 { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static ZooKeeper zookeeper = null; public static void main(String[] args) throws Exception { String path = "/zk-book-5"; zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override 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 { zookeeper.getData(event.getPath(), true, new IDataCallback(), null); } catch (Exception e) { } } } } }); connectedSemaphore.await(); zookeeper.create(path, "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); System.out.println("success create znode: " + path); zookeeper.getData(path, true, new IDataCallback(), null); zookeeper.setData(path, "1234".getBytes(), -1); Thread.sleep(Integer.MAX_VALUE); }}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()); }}
结果表明采用异步方式同样可方便获取节点的数据。
3.5 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.npf.test;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 ZookeeperSetDataAPITest { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static ZooKeeper zookeeper = null; public static void main(String[] args) throws Exception { String path = "/zk-book-6"; zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override public void process(WatchedEvent event) { if (KeeperState.SyncConnected == event.getState()) { if (EventType.None == event.getType() && null == event.getPath()) { connectedSemaphore.countDown(); } } } }); connectedSemaphore.await(); zookeeper.create(path, "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); System.out.println("success create znode: " + path); zookeeper.getData(path, true, null); Stat stat = zookeeper.setData(path, "456".getBytes(), -1); System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " + stat.getVersion()); Stat stat2 = zookeeper.setData(path, "456".getBytes(), stat.getVersion()); System.out.println("czxID: " + stat2.getCzxid() + ", mzxID: " + stat2.getMzxid() + ", version: " + stat2.getVersion()); try { zookeeper.setData(path, "456".getBytes(), stat.getVersion()); } catch (KeeperException e) { System.out.println("Error: " + e.code() + "," + e.getMessage()); } Thread.sleep(Integer.MAX_VALUE); }}
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.npf.test;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 ZookeeperSetDataAPITest2 { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); public static ZooKeeper zookeeper = null; public static void main(String[] args) throws Exception { String path = "/zk-book-7"; zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override public void process(WatchedEvent event) { if (KeeperState.SyncConnected == event.getState()) { if (EventType.None == event.getType() && null == event.getPath()) { connectedSemaphore.countDown(); } } } }); connectedSemaphore.await(); zookeeper.create(path, "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); System.out.println("success create znode: " + path); zookeeper .setData(path, "456".getBytes(), -1, new IStatCallback(), null); Thread.sleep(Integer.MAX_VALUE); }}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); }}
rc（ResultCode）为0，表明成功更新节点数据。
3.6 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.npf.test;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 ZookeeperNodeExistAPITest { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); static ZooKeeper zookeeper = null; public static void main(String[] args) throws Exception { String path = "/zk-book"; zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override 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()); zookeeper.exists(event.getPath(), true); } else if (EventType.NodeDeleted == event.getType()) { System.out.println("success delete znode: " + event.getPath()); zookeeper.exists(event.getPath(), true); } else if (EventType.NodeDataChanged == event.getType()) { System.out.println("data changed of znode: " + event.getPath()); zookeeper.exists(event.getPath(), true); } } } catch (Exception e) { } } }); connectedSemaphore.await(); zookeeper.exists(path, true); zookeeper.create(path, "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); zookeeper.setData(path, "123".getBytes(), -1); zookeeper.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); System.out.println("success create znode: " + path + "/c1"); zookeeper.delete(path + "/c1", -1); zookeeper.delete(path, -1); Thread.sleep(Integer.MAX_VALUE); }}运行结果如下:
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.npf.test;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 ZookeeperNodeExistAPITest2 { private static CountDownLatch connectedSemaphore = new CountDownLatch(1); static ZooKeeper zookeeper = null; public static void main(String[] args) throws Exception { String path = "/zk-book"; zookeeper = new ZooKeeper("npfdev1:2181", 5000, new Watcher() { @Override 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()); zookeeper.exists(event.getPath(), true, new IIStatCallback(), null); } else if (EventType.NodeDeleted == event.getType()) { System.out.println("success delete znode: " + event.getPath()); zookeeper.exists(event.getPath(), true, new IIStatCallback(), null); } else if (EventType.NodeDataChanged == event.getType()) { System.out.println("data changed of znode: " + event.getPath()); zookeeper.exists(event.getPath(), true, new IIStatCallback(), null); } } } catch (Exception e) { } } }); connectedSemaphore.await(); zookeeper.exists(path, true, new IIStatCallback(), null); zookeeper.create(path, "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); zookeeper.setData(path, "123".getBytes(), -1); zookeeper.create(path + "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); System.out.println("success create znode: " + path + "/c1"); zookeeper.delete(path + "/c1", -1); zookeeper.delete(path, -1); Thread.sleep(Integer.MAX_VALUE); }}class IIStatCallback implements AsyncCallback.StatCallback { @Override 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:
结果表明当节点不存在时，其rc（ResultCode）为-101。
3.7 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.npf.test;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("npfdev1:2181", 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("npfdev1:2181", 5000, null); zookeeper2.getData(PATH, false, null); }}运行结果如下:
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.npf.test;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("npfdev1:2181", 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("npfdev1:2181", 5000, null); zookeeper2.delete(PATH2, -1); } catch (Exception e) { System.out.println("fail to delete: " + e.getMessage()); } ZooKeeper zookeeper3 = new ZooKeeper("npfdev1:2181", 5000, null); zookeeper3.addAuthInfo("digest", "foo:true".getBytes()); zookeeper3.delete(PATH2, -1); System.out.println("success delete znode: " + PATH2); ZooKeeper zookeeper4 = new ZooKeeper("npfdev1:2181", 5000, null); zookeeper4.delete(PATH, -1); System.out.println("success delete znode: " + PATH); }}运行结果如下:
结果表明若没有权限，则无法删除节点。
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