Apache Curator入门实战
Curator是Netflix公司开源的一个Zookeeper客户端，与Zookeeper提供的原生客户端相比，Curator的抽象层次更高，简化了Zookeeper客户端的开发量。
1.Zookeeper安装部署Zookeeper的部署很简单，如果已经有Java运行环境的话，下载tarball解压后即可运行。
[root@linuxidc Temp]$ wget http://mirror.bit.edu.cn/apache/zookeeper/zookeeper-3.4.6/zookeeper-3.4.6.tar.gz [root@linuxidc Temp]$ tar zxvf zookeeper-3.4.6.tar.gz [root@linuxidc Temp]$ cd zookeeper-3.4.6 [root@linuxidc zookeeper-3.4.6]$ cp conf/zoo_sample.cfg conf/zoo.cfg [root@linuxidc zookeeper-3.4.6]$ export ZOOKEEPER_HOME=/usr/local/src/zookeeper-3.4.5 [root@linuxidc zookeeper-3.4.6]$ export PATH=$ZOOKEEPER_HOME/bin:$PATH [root@linuxidc zookeeper-3.4.6]$ bin/zkServer.sh start [root@linuxidc zookeeper-3.4.6]$ bin/zkCli.sh -server 127.0.0.1:2181 2.客户端常用操作用zkCli.sh连接上Zookeeper服务后，用help能列出所有命令：
[root@BC-VM-edce4ac67d304079868c0bb265337bd4 zookeeper-3.4.6]# bin/zkCli.sh -127.0.0.1:2181 Connecting to localhost:2181 2015-06-11 10:55:14,387 [myid:] - INFO [main:Environment@100] - Client environment:zookeeper.version=3.4.6-1569965, built on 02/20/2014 09:09 GMT ... [zk: localhost:2181(CONNECTED) 5] help ZooKeeper -server host:port cmd args connect host:port get path [watch] ls path [watch] set path data [version] rmr path delquota [-n|-b] path quit printwatches on|off create [-s] [-e] path data acl stat path [watch] close ls2 path [watch] history listquota path setAcl path acl getAcl path sync path redo cmdno addauth scheme auth delete path [version] setquota -n|-b val path下面就试验一下常用的命令：
create：创建路径结点。
ls：查看路径下的所有结点。
get：获得结点上的值。
set：修改结点上的值。
delete：删除结点。
[zk: localhost:2181(CONNECTED) 6] create /zktest mydata Created /zktest [zk: localhost:2181(CONNECTED) 12] ls / [zktest, zookeeper] [zk: localhost:2181(CONNECTED) 7] ls /zktest [] [zk: localhost:2181(CONNECTED) 13] get /zktest mydata cZxid = 0x1c ctime = Thu Jun 11 10:58:06 CST 2015 mZxid = 0x1c mtime = Thu Jun 11 10:58:06 CST 2015 pZxid = 0x1c cversion = 0 dataVersion = 0 aclVersion = 0 ephemeralOwner = 0x0 dataLength = 6 numChildren = 0 [zk: localhost:2181(CONNECTED) 14] set /zktest junk cZxid = 0x1c ctime = Thu Jun 11 10:58:06 CST 2015 mZxid = 0x1f mtime = Thu Jun 11 10:59:08 CST 2015 pZxid = 0x1c cversion = 0 dataVersion = 1 aclVersion = 0 ephemeralOwner = 0x0 dataLength = 4 numChildren = 0 [zk: localhost:2181(CONNECTED) 15] delete /zktest [zk: localhost:2181(CONNECTED) 16] ls / [zookeeper] 3.用Curator管理ZookeeperCurator的Maven依赖如下，一般直接使用curator-recipes就行了，如果需要自己封装一些底层些的功能的话，例如增加连接管理重试机制等，则可以引入curator-framework包。
<dependency> <groupId>org.apache.curator</groupId> <artifactId>curator-recipes</artifactId> <version>2.7.0</version> </dependency> 3.1 Client操作利用Curator提供的客户端API，可以完全实现上面原生客户端的功能。值得注意的是，Curator采用流式风格API。
package com.cdai.codebase.bigdata.Hadoop.zookeeper.curator; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.retry.RetryNTimes; /** * Curator framework's client test. * Output: * $ create /zktest hello * $ ls / * [zktest, zookeeper] * $ get /zktest * hello * $ set /zktest world * $ get /zktest * world * $ delete /zktest * $ ls / * [zookeeper] */ public class CuratorClientTest { /** Zookeeper info */ private static final String ZK_ADDRESS = "192.168.1.100:2181"; private static final String ZK_PATH = "/zktest"; public static void main(String[] args) throws Exception { // 1.Connect to zk CuratorFramework client = CuratorFrameworkFactory.newClient( ZK_ADDRESS, new RetryNTimes(10, 5000) ); client.start(); System.out.println("zk client start successfully!"); // 2.Client API test // 2.1 Create node String data1 = "hello"; print("create", ZK_PATH, data1); client.create(). creatingParentsIfNeeded(). forPath(ZK_PATH, data1.getBytes()); // 2.2 Get node and data print("ls", "/"); print(client.getChildren().forPath("/")); print("get", ZK_PATH); print(client.getData().forPath(ZK_PATH)); // 2.3 Modify data String data2 = "world"; print("set", ZK_PATH, data2); client.setData().forPath(ZK_PATH, data2.getBytes()); print("get", ZK_PATH); print(client.getData().forPath(ZK_PATH)); // 2.4 Remove node print("delete", ZK_PATH); client.delete().forPath(ZK_PATH); print("ls", "/"); print(client.getChildren().forPath("/")); } private static void print(String... cmds) { StringBuilder text = new StringBuilder("$ "); for (String cmd : cmds) { text.append(cmd).append(" "); } System.out.println(text.toString()); } private static void print(Object result) { System.out.println( result instanceof byte[] ? new String((byte[]) result) : result); } } 3.2 监听器Curator提供了三种Watcher(Cache)来监听结点的变化：
Path Cache：监视一个路径下1）孩子结点的创建、2）删除，3）以及结点数据的更新。产生的事件会传递给注册的PathChildrenCacheListener。
Node Cache：监视一个结点的创建、更新、删除，并将结点的数据缓存在本地。
Tree Cache：Path Cache和Node Cache的“合体”，监视路径下的创建、更新、删除事件，并缓存路径下所有孩子结点的数据。