一、前言
上一篇博客已经介绍了如何使用Zookeeper提供的原生态Java API进行操作，本篇博文主要讲解如何通过开源客户端来进行操作。
二、ZkClient
ZkClient是在Zookeeper原声API接口之上进行了包装，是一个更易用的Zookeeper客户端，其内部还实现了诸如Session超时重连、Watcher反复注册等功能。
2.1 添加依赖
在pom.xml文件中添加如下内容即可。
<dependency> <groupId>com.101tecgroupId> <artifactId>zkclientartifactId> <version>0.2version> dependency>
2.2 创建会话
使用ZkClient可以轻松的创建会话，连接到服务端。
package com.hust.grid.leesf.zkclient.examples; import java.io.IOException; import org.I0Itec.zkclient.ZkClient; public class Create_Session_Sample { public static void main(String[] args) throws IOException, InterruptedException { ZkClient zkClient = new ZkClient("127.0.0.1:2181", 5000); System.out.println("ZooKeeper session established."); } }
运行结果：
ZooKeeper session established.
结果表明已经成功创建会话。
2.3 创建节点
ZkClient提供了递归创建节点的接口，即其帮助开发者完成父节点的创建，再创建子节点。
package com.hust.grid.leesf.zkclient.examples; import org.I0Itec.zkclient.ZkClient; public class Create_Node_Sample { public static void main(String[] args) throws Exception { ZkClient zkClient = new ZkClient("127.0.0.1:2181", 5000); String path = "/zk-book/c1"; zkClient.createPersistent(path, true); System.out.println("success create znode."); } }
运行结果：
success create znode.
结果表明已经成功创建了节点，值得注意的是，在原生态接口中是无法创建成功的（父节点不存在），但是通过ZkClient可以递归的先创建父节点，再创建子节点。
可以看到确实成功创建了/zk-book和/zk-book/c1两个节点。
2.4 删除节点
ZkClient提供了递归删除节点的接口，即其帮助开发者先删除所有子节点（存在），再删除父节点。
package com.hust.grid.leesf.zkclient.examples; import org.I0Itec.zkclient.ZkClient; public class Del_Data_Sample { public static void main(String[] args) throws Exception { String path = "/zk-book"; ZkClient zkClient = new ZkClient("127.0.0.1:2181", 5000); zkClient.createPersistent(path, ""); zkClient.createPersistent(path+"/c1", ""); zkClient.deleteRecursive(path); System.out.println("success delete znode."); } }
运行结果:
success delete znode.
结果表明ZkClient可直接删除带子节点的父节点，因为其底层先删除其所有子节点，然后再删除父节点。
2.5 获取子节点
package com.hust.grid.leesf.zkclient.examples; import java.util.List; import org.I0Itec.zkclient.IZkChildListener; import org.I0Itec.zkclient.ZkClient; public class Get_Children_Sample { public static void main(String[] args) throws Exception { String path = "/zk-book"; ZkClient zkClient = new ZkClient("127.0.0.1:2181", 5000); zkClient.subscribeChildChanges(path, new IZkChildListener() { public void handleChildChange(String parentPath, ListcurrentChilds) throws Exception { System.out.println(parentPath + " 's child changed, currentChilds:" + currentChilds); } }); zkClient.createPersistent(path); Thread.sleep(1000); zkClient.createPersistent(path + "/c1"); Thread.sleep(1000); zkClient.delete(path + "/c1"); Thread.sleep(1000); zkClient.delete(path); Thread.sleep(Integer.MAX_VALUE); } }
运行结果：
/zk-book 's child changed, currentChilds:[] /zk-book 's child changed, currentChilds:[c1] /zk-book 's child changed, currentChilds:[] /zk-book 's child changed, currentChilds:null
结果表明：
客户端可以对一个不存在的节点进行子节点变更的监听。
一旦客户端对一个节点注册了子节点列表变更监听之后，那么当该节点的子节点列表发生变更时，服务端都会通知客户端，并将最新的子节点列表发送给客户端
该节点本身的创建或删除也会通知到客户端。
2.6 获取数据
package com.hust.grid.leesf.zkclient.examples; import org.I0Itec.zkclient.IZkDataListener; import org.I0Itec.zkclient.ZkClient; public class Get_Data_Sample { public static void main(String[] args) throws Exception { String path = "/zk-book"; ZkClient zkClient = new ZkClient("127.0.0.1:2181", 5000); zkClient.createEphemeral(path, "123"); zkClient.subscribeDataChanges(path, new IZkDataListener() { public void handleDataDeleted(String dataPath) throws Exception { System.out.println("Node " + dataPath + " deleted."); } public void handleDataChange(String dataPath, Object data) throws Exception { System.out.println("Node " + dataPath + " changed, new data: " + data); } }); System.out.println(zkClient.readData(path)); zkClient.writeData(path, "456"); Thread.sleep(1000); zkClient.delete(path); Thread.sleep(Integer.MAX_VALUE); } }
运行结果：
123 Node /zk-book changed, new data: 456 Node /zk-book deleted.
结果表明可以成功监听节点数据变化或删除事件。
2.7 检测节点是否存在
package com.hust.grid.leesf.zkclient.examples; import org.I0Itec.zkclient.ZkClient; public class Exist_Node_Sample { public static void main(String[] args) throws Exception { String path = "/zk-book"; ZkClient zkClient = new ZkClient("127.0.0.1:2181", 2000); System.out.println("Node " + path + " exists " + zkClient.exists(path)); } }
运行结果：
Node /zk-book exists false
结果表明，可以通过ZkClient轻易检测节点是否存在，其相比于原生态的接口更易于理解。
三、Curator客户端
Curator解决了很多Zookeeper客户端非常底层的细节开发工作，包括连接重连，反复注册Watcher和NodeExistsException异常等，现已成为Apache的顶级项目。
3.1 添加依赖
在pom.xml文件中添加如下内容即可。
<dependency>
<groupId>org.apache.curatorgroupId>
<artifactId>curator-frameworkartifactId>
<version>2.4.2version>
dependency>
3.2 创建会话
Curator除了使用一般方法创建会话外，还可以使用fluent风格进行创建。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.RetryPolicy; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.retry.ExponentialBackoffRetry; public class Create_Session_Sample { public static void main(String[] args) throws Exception { RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3); CuratorFramework client = CuratorFrameworkFactory.newClient("127.0.0.1:2181", 5000, 3000, retryPolicy); client.start(); System.out.println("Zookeeper session1 established. "); CuratorFramework client1 = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .sessionTimeoutMs(5000).retryPolicy(retryPolicy).namespace("base").build(); client1.start(); System.out.println("Zookeeper session2 established. "); } }
运行结果：
Zookeeper session1 established.
Zookeeper session2 established.
值得注意的是session2会话含有隔离命名空间，即客户端对Zookeeper上数据节点的任何操作都是相对/base目录进行的，这有利于实现不同的Zookeeper的业务之间的隔离。
3.3 创建节点
通过使用Fluent风格的接口，开发人员可以进行自由组合来完成各种类型节点的创建。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.retry.ExponentialBackoffRetry; import org.apache.zookeeper.CreateMode; public class Create_Node_Sample { public static void main(String[] args) throws Exception { String path = "/zk-book/c1"; CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); client.start(); client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "init".getBytes()); System.out.println("success create znode: " + path); } }
运行结果：
success create znode: /zk-book/c1
其中，也创建了/zk-book/c1的父节点/zk-book节点。
3.4 删除节点
package com.hust.grid.leesf.curator.examples; 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; public class Del_Data_Sample { public static void main(String[] args) throws Exception { String path = "/zk-book/c1"; CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); client.start(); client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "init".getBytes()); Stat stat = new Stat(); System.out.println(new String(client.getData().storingStatIn(stat).forPath(path))); client.delete().deletingChildrenIfNeeded().withVersion(stat.getVersion()).forPath(path); System.out.println("success delete znode " + path); Thread.sleep(Integer.MAX_VALUE); } }
运行结果：
init
success delete znode /zk-book/c1
结果表明成功删除/zk-book/c1节点。
3.5 获取数据
package com.hust.grid.leesf.curator.examples; 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; public class Get_Data_Sample { public static void main(String[] args) throws Exception { String path = "/zk-book"; CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); client.start(); client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "init".getBytes()); Stat stat = new Stat(); System.out.println(new String(client.getData().storingStatIn(stat).forPath(path))); } }
运行结果：
init
结果表明成功获取了节点的数据。
3.6 更新数据
package com.hust.grid.leesf.curator.examples; 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; public class Set_Data_Sample { public static void main(String[] args) throws Exception { String path = "/zk-book"; CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); client.start(); client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "init".getBytes()); Stat stat = new Stat(); client.getData().storingStatIn(stat).forPath(path); System.out.println("Success set node for : " + path + ", new version: " + client.setData().withVersion(stat.getVersion()).forPath(path).getVersion()); try { client.setData().withVersion(stat.getVersion()).forPath(path); } catch (Exception e) { System.out.println("Fail set node due to " + e.getMessage()); } } }
运行结果：
Success set node for : /zk-book, new version: 1 Fail set node due to KeeperErrorCode = BadVersion for /zk-book
结果表明当携带数据版本不一致时，无法完成更新操作。
3.7 异步接口
如同Zookeeper原生API提供了异步接口，Curator也提供了异步接口。在Zookeeper中，所有的异步通知事件处理都是由EventThread这个线程来处理的，EventThread线程用于串行处理所有的事件通知，其可以保证对事件处理的顺序性，但是一旦碰上复杂的处理单元，会消耗过长的处理时间，从而影响其他事件的处理，Curator允许用户传入Executor实例，这样可以将比较复杂的事件处理放到一个专门的线程池中去。
package com.hust.grid.leesf.curator.examples; 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; public class Create_Node_Background_Sample { static String path = "/zk-book"; static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); static CountDownLatch semaphore = new CountDownLatch(2); static ExecutorService tp = Executors.newFixedThreadPool(2); public static void main(String[] args) throws Exception { client.start(); System.out.println("Main thread: " + Thread.currentThread().getName()); 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() + "]" + ", Thread of processResult: " + Thread.currentThread().getName()); System.out.println(); semaphore.countDown(); } }, tp).forPath(path, "init".getBytes()); 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() + "]" + ", Thread of processResult: " + Thread.currentThread().getName()); semaphore.countDown(); } }).forPath(path, "init".getBytes()); semaphore.await(); tp.shutdown(); } }
运行结果：
Main thread: main event[code: -110, type: CREATE], Thread of processResult: main-EventThread event[code: 0, type: CREATE], Thread of processResult: pool-3-thread-1
其中，创建节点的事件由线程池自己处理，而非默认线程处理。
Curator除了提供很便利的API，还提供了一些典型的应用场景，开发人员可以使用参考更好的理解如何使用Zookeeper客户端，所有的都在recipes包中，只需要在pom.xml中添加如下依赖即可
<dependency> <groupId>org.apache.curatorgroupId> <artifactId>curator-recipesartifactId> <version>2.4.2version>
dependency>
3.8 节点监听
package com.hust.grid.leesf.curator.examples; 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; public class NodeCache_Sample { static String path = "/zk-book/nodecache"; static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception { client.start(); client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "init".getBytes()); final NodeCache cache = new NodeCache(client, path, false); cache.start(true); cache.getListenable().addListener(new NodeCacheListener() { public void nodeChanged() throws Exception { System.out.println("Node data update, new data: " + new String(cache.getCurrentData().getData())); } }); client.setData().forPath(path, "u".getBytes()); Thread.sleep(1000); client.delete().deletingChildrenIfNeeded().forPath(path); Thread.sleep(Integer.MAX_VALUE); } }
运行结果：
Node data update, new data: u
当节点数据变更后收到了通知。NodeCache不仅可以监听数据节点的内容变更，也能监听指定节点是否存在。
3.9 子节点监听
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.cache.PathChildrenCache; import org.apache.curator.framework.recipes.cache.PathChildrenCache.StartMode; import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent; import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener; import org.apache.curator.retry.ExponentialBackoffRetry; import org.apache.zookeeper.CreateMode; public class PathChildrenCache_Sample { static String path = "/zk-book"; static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .retryPolicy(new ExponentialBackoffRetry(1000, 3)).sessionTimeoutMs(5000).build(); public static void main(String[] args) throws Exception { client.start(); PathChildrenCache cache = new PathChildrenCache(client, path, true); cache.start(StartMode.POST_INITIALIZED_EVENT); cache.getListenable().addListener(new PathChildrenCacheListener() { public void childEvent(CuratorFramework client, PathChildrenCacheEvent event) throws Exception { switch (event.getType()) { case CHILD_ADDED: System.out.println("CHILD_ADDED," + event.getData().getPath()); break; case CHILD_UPDATED: System.out.println("CHILD_UPDATED," + event.getData().getPath()); break; case CHILD_REMOVED: System.out.println("CHILD_REMOVED," + event.getData().getPath()); break; default: break; } } }); client.create().withMode(CreateMode.PERSISTENT).forPath(path); Thread.sleep(1000); client.create().withMode(CreateMode.PERSISTENT).forPath(path + "/c1"); Thread.sleep(1000); client.delete().forPath(path + "/c1"); Thread.sleep(1000); client.delete().forPath(path); Thread.sleep(Integer.MAX_VALUE); } }
运行结果：
CHILD_ADDED,/zk-book/c1
CHILD_REMOVED,/zk-book/c1
监听节点的子节点，包括新增、数据变化、删除三类事件。
3.10 Master选举
借助Zookeeper，开发者可以很方便地实现Master选举功能，其大体思路如下：选择一个根节点，如/master_select，多台机器同时向该节点创建一个子节点/master_select/lock，利用Zookeeper特性，最终只有一台机器能够成功创建，成功的那台机器就是Master。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.leader.LeaderSelector; import org.apache.curator.framework.recipes.leader.LeaderSelectorListenerAdapter; import org.apache.curator.retry.ExponentialBackoffRetry; public class Recipes_MasterSelect { static String master_path = "/curator_recipes_master_path"; static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception { client.start(); LeaderSelector selector = new LeaderSelector(client, master_path, new LeaderSelectorListenerAdapter() { public void takeLeadership(CuratorFramework client) throws Exception { System.out.println("成为Master角色"); Thread.sleep(3000); System.out.println("完成Master操作，释放Master权利"); } }); selector.autoRequeue(); selector.start(); Thread.sleep(Integer.MAX_VALUE); } }
运行结果：
成为Master角色
完成Master操作，释放Master权利
成为Master角色
以上结果会反复循环，并且当一个应用程序完成Master逻辑后，另外一个应用程序的相应方法才会被调用，即当一个应用实例成为Master后，其他应用实例会进入等待，直到当前Master挂了或者推出后才会开始选举Master。
3.11 分布式锁
为了保证数据的一致性，经常在程序的某个运行点需要进行同步控制。以流水号生成场景为例，普通的后台应用通常采用时间戳方式来生成流水号，但是在用户量非常大的情况下，可能会出现并发问题。
package com.hust.grid.leesf.curator.examples; import java.text.SimpleDateFormat; import java.util.Date; import java.util.concurrent.CountDownLatch; public class Recipes_NoLock { public static void main(String[] args) throws Exception { final CountDownLatch down = new CountDownLatch(1); for (int i = 0; i < 10; i++) { new Thread(new Runnable() { public void run() { try { down.await(); } catch (Exception e) { } SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss|SSS"); String orderNo = sdf.format(new Date()); System.err.println("生成的订单号是 : " + orderNo); } }).start(); } down.countDown(); } }
运行结果：
生成的订单号是 : 16:29:10|590 生成的订单号是 : 16:29:10|590 生成的订单号是 : 16:29:10|591 生成的订单号是 : 16:29:10|591 生成的订单号是 : 16:29:10|590 生成的订单号是 : 16:29:10|590 生成的订单号是 : 16:29:10|591 生成的订单号是 : 16:29:10|590 生成的订单号是 : 16:29:10|592 生成的订单号是 : 16:29:10|591
结果表示订单号出现了重复，即普通的方法无法满足业务需要，因为其未进行正确的同步。可以使用Curator来实现分布式锁功能。
package com.hust.grid.leesf.curator.examples; import java.text.SimpleDateFormat; import java.util.Date; import java.util.concurrent.CountDownLatch; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.locks.InterProcessMutex; import org.apache.curator.retry.ExponentialBackoffRetry; public class Recipes_Lock { static String lock_path = "/curator_recipes_lock_path"; static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception { client.start(); final InterProcessMutex lock = new InterProcessMutex(client, lock_path); final CountDownLatch down = new CountDownLatch(1); for (int i = 0; i < 30; i++) { new Thread(new Runnable() { public void run() { try { down.await(); lock.acquire(); } catch (Exception e) { } SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss|SSS"); String orderNo = sdf.format(new Date()); System.out.println("生成的订单号是 : " + orderNo); try { lock.release(); } catch (Exception e) { } } }).start(); } down.countDown(); } }
运行结果：
生成的订单号是 : 16:31:50|293 生成的订单号是 : 16:31:50|319 生成的订单号是 : 16:31:51|278 生成的订单号是 : 16:31:51|326 生成的订单号是 : 16:31:51|402 生成的订单号是 : 16:31:51|420 生成的订单号是 : 16:31:51|546 生成的订单号是 : 16:31:51|602 生成的订单号是 : 16:31:51|626 生成的订单号是 : 16:31:51|656 生成的订单号是 : 16:31:51|675 生成的订单号是 : 16:31:51|701 生成的订单号是 : 16:31:51|708 生成的订单号是 : 16:31:51|732 生成的订单号是 : 16:31:51|763 生成的订单号是 : 16:31:51|785 生成的订单号是 : 16:31:51|805 生成的订单号是 : 16:31:51|823 生成的订单号是 : 16:31:51|839 生成的订单号是 : 16:31:51|853 生成的订单号是 : 16:31:51|868 生成的订单号是 : 16:31:51|884 生成的订单号是 : 16:31:51|897 生成的订单号是 : 16:31:51|910 生成的订单号是 : 16:31:51|926 生成的订单号是 : 16:31:51|939 生成的订单号是 : 16:31:51|951 生成的订单号是 : 16:31:51|965 生成的订单号是 : 16:31:51|972 生成的订单号是 : 16:31:51|983
结果表明此时已经不存在重复的流水号。
3.12 分布式计数器
分布式计数器的典型应用是统计系统的在线人数，借助Zookeeper也可以很方便实现分布式计数器功能：指定一个Zookeeper数据节点作为计数器，多个应用实例在分布式锁的控制下，通过更新节点的内容来实现计数功能。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.atomic.AtomicValue; import org.apache.curator.framework.recipes.atomic.DistributedAtomicInteger; import org.apache.curator.retry.ExponentialBackoffRetry; import org.apache.curator.retry.RetryNTimes; public class Recipes_DistAtomicInt { static String distatomicint_path = "/curator_recipes_distatomicint_path"; static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception { client.start(); DistributedAtomicInteger atomicInteger = new DistributedAtomicInteger(client, distatomicint_path, new RetryNTimes(3, 1000)); AtomicValuerc = atomicInteger.add(8); System.out.println("Result: " + rc.succeeded()); } }
运行结果：
Result: true
结果表明已经将数据成功写入数据节点中。
3.13 分布式Barrier
如同JDK的CyclicBarrier，Curator提供了DistributedBarrier来实现分布式Barrier。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.barriers.DistributedBarrier; import org.apache.curator.retry.ExponentialBackoffRetry; public class Recipes_Barrier { static String barrier_path = "/curator_recipes_barrier_path"; static DistributedBarrier barrier; public static void main(String[] args) throws Exception { for (int i = 0; i < 5; i++) { new Thread(new Runnable() { public void run() { try { CuratorFramework client = CuratorFrameworkFactory.builder() .connectString("127.0.0.1:2181") .retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); client.start(); barrier = new DistributedBarrier(client, barrier_path); System.out.println(Thread.currentThread().getName() + "号barrier设置"); barrier.setBarrier(); barrier.waitOnBarrier(); System.err.println("启动..."); } catch (Exception e) { } } }).start(); } Thread.sleep(2000); barrier.removeBarrier(); } }
运行结果：
Thread-1号barrier设置 Thread-2号barrier设置 Thread-4号barrier设置 Thread-3号barrier设置 Thread-0号barrier设置 启动... 启动... 启动... 启动... 启动...
结果表明通过DistributedBarrier可以实现类似于CyclicBarrier的分布式Barrier功能。
四、Curator工具类
4.1 ZKPaths
其提供了简单的API来构建znode路径、递归创建、删除节点等。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.retry.ExponentialBackoffRetry; import org.apache.curator.utils.ZKPaths; import org.apache.curator.utils.ZKPaths.PathAndNode; import org.apache.zookeeper.ZooKeeper; public class ZKPaths_Sample { static String path = "/curator_zkpath_sample"; static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception { client.start(); ZooKeeper zookeeper = client.getZookeeperClient().getZooKeeper(); System.out.println(ZKPaths.fixForNamespace(path, "sub")); System.out.println(ZKPaths.makePath(path, "sub")); System.out.println(ZKPaths.getNodeFromPath("/curator_zkpath_sample/sub1")); PathAndNode pn = ZKPaths.getPathAndNode("/curator_zkpath_sample/sub1"); System.out.println(pn.getPath()); System.out.println(pn.getNode()); String dir1 = path + "/child1"; String dir2 = path + "/child2"; ZKPaths.mkdirs(zookeeper, dir1); ZKPaths.mkdirs(zookeeper, dir2); System.out.println(ZKPaths.getSortedChildren(zookeeper, path)); ZKPaths.deleteChildren(client.getZookeeperClient().getZooKeeper(), path, true); } }
运行结果：
/curator_zkpath_sample/sub /curator_zkpath_sample/sub sub1 /curator_zkpath_sample sub1 [child1, child2]
借助ZKPaths可快速方便的完成节点的创建等操作。
4.2 EnsurePath
其提供了一种能够确保数据节点存在的机制，当上层业务希望对一个数据节点进行操作时，操作前需要确保该节点存在。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.retry.ExponentialBackoffRetry; import org.apache.curator.utils.EnsurePath; public class EnsurePathDemo { static String path = "/zk-book/c1"; static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception { client.start(); client.usingNamespace("zk-book"); EnsurePath ensurePath = new EnsurePath(path); ensurePath.ensure(client.getZookeeperClient()); ensurePath.ensure(client.getZookeeperClient()); EnsurePath ensurePath2 = client.newNamespaceAwareEnsurePath("/c1"); ensurePath2.ensure(client.getZookeeperClient()); } }
EnsurePath采取了如下节点创建方式，试图创建指定节点，如果节点已经存在，那么就不进行任何操作，也不对外抛出异常，否则正常创建数据节点。
五、总结
本篇介绍了使用Zookeeper的开源客户端如何操作Zookeeper的方法，相应的源码也已经上传至github，谢谢各位园友的观看～