掌握zookeeper事件监听机制，非常重要，可以说是跨入了进阶的门槛，只有掌握了如何监听某个节点或路径，我们才能在节点变化后，做一些我们想做的事，包括： 
1，配置文件同步 
2，主从切换 
3，分布式队列 
4，分布式锁 
5，其他

本篇我们就来看下，如何使用curator来完成监听，代码如下：

 package com.qin.curator.zk;

 import javax.sound.midi.Patch;

 import org.apache.curator.RetryPolicy;

 import org.apache.curator.framework.CuratorFramework;

 import org.apache.curator.framework.CuratorFrameworkFactory;

 import org.apache.curator.framework.CuratorFrameworkFactory.Builder;

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

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

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

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

 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.curator.utils.ZKPaths;

 import org.apache.zookeeper.WatchedEvent;

 /**

  *

  * 使用curator监听zookeeper节点

  * @author qindongliang

  * **/

 public class CuratorWatch {

     static CuratorFramework zkclient=null;

     static String nameSpace="php";

     static {

           String zkhost="192.168.46.22:2181";//zk的host

           RetryPolicy rp=new ExponentialBackoffRetry(1000, 3);//重试机制

           Builder builder = CuratorFrameworkFactory.builder().connectString(zkhost)

                   .connectionTimeoutMs(5000)

                   .sessionTimeoutMs(5000)

                   .retryPolicy(rp);

           builder.namespace(nameSpace);

           CuratorFramework zclient = builder.build();

           zkclient=zclient;

           zkclient.start();// 放在这前面执行

           zkclient.newNamespaceAwareEnsurePath(nameSpace);

     }

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

         watch();

         Thread.sleep(Long.MAX_VALUE);

     }

     /**

      *

      * 监听节点变化

      *

      * */

     public static void watch()throws Exception{

         PathChildrenCache cache = new PathChildrenCache(zkclient, "/zk", false);

         cache.start();

         System.out.println("监听开始/zk........");

         PathChildrenCacheListener plis=new PathChildrenCacheListener() {

             @Override

             public void childEvent(CuratorFramework client, PathChildrenCacheEvent event)

                     throws Exception {

                   switch ( event.getType() )

                     {

                         case CHILD_ADDED:

                         {

                             System.out.println("Node added: " + ZKPaths.getNodeFromPath(event.getData().getPath()));

                             break;

                         }

                         case CHILD_UPDATED:

                         {

                             System.out.println("Node changed: " + ZKPaths.getNodeFromPath(event.getData().getPath()));

                             break;

                         }

                         case CHILD_REMOVED:

                         {

                             System.out.println("Node removed: " + ZKPaths.getNodeFromPath(event.getData().getPath()));

                             break;

                         }

                     }

             }

         };

         //注册监听

         cache.getListenable().addListener(plis);

     }

 }

运行后的控制台打印：

 18:33:07.722 [main] INFO  o.a.c.f.imps.CuratorFrameworkImpl - Starting

 18:33:07.727 [main] DEBUG o.a.curator.CuratorZookeeperClient - Starting

 18:33:07.727 [main] DEBUG org.apache.curator.ConnectionState - Starting

 18:33:07.727 [main] DEBUG org.apache.curator.ConnectionState - reset

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:zookeeper.version=3.4.6-1569965, built on 02/20/2014 09:09 GMT

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:host.name=QINDONGLIANG.dhgatecn.msf

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.version=1.7.0_04

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.vendor=Oracle Corporation

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.home=D:\Java\jdk1.7.0_04\jre

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.class.path=D:\eclipseworkspace2yw\opzk\bin;D:\eclipseworkspace2yw\opzk\lib\curator-client-2.6.0.jar;D:\eclipseworkspace2yw\opzk\lib\curator-examples-2.6.0.jar;D:\eclipseworkspace2yw\opzk\lib\curator-framework-2.6.0.jar;D:\eclipseworkspace2yw\opzk\lib\curator-recipes-2.6.0.jar;D:\eclipseworkspace2yw\opzk\lib\curator-test-2.6.0.jar;D:\eclipseworkspace2yw\opzk\lib\curator-x-discovery-2.6.0.jar;D:\eclipseworkspace2yw\opzk\lib\curator-x-discovery-server-2.6.0.jar;D:\eclipseworkspace2yw\opzk\lib\curator-x-rpc-2.6.0.jar;D:\eclipseworkspace2yw\opzk\lib\log4j-1.2.15.jar;D:\eclipseworkspace2yw\opzk\lib\zookeeper-3.4.5.jar;D:\eclipseworkspace2yw\opzk\lib\commons-io-2.1.jar

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.library.path=D:\Java\jdk1.7.0_04\bin;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;D:/Java/jdk1.7.0_04/bin/../jre/bin/server;D:/Java/jdk1.7.0_04/bin/../jre/bin;D:/Java/jdk1.7.0_04/bin/../jre/lib/amd64;C:\Program Files\Common Files\Microsoft Shared\Windows Live;C:\Program Files (x86)\Common Files\Microsoft Shared\Windows Live;D:\Java\jdk1.7.0_04\bin;D:\Java\jdk1.7.0_04\jre\bin;D:\apache-ant-1.9.3\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files (x86)\Lenovo\Lenovo Home\;C:\Program Files (x86)\Windows Live\Shared;C:\Program Files\TortoiseSVN\bin;D:\hadoop-2.2.0/bin;C:\MyProgramFiles\apache-maven-3.0.5\bin;D:\python;E:\eclipse;;.

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.io.tmpdir=C:\Users\QINDON~1\AppData\Local\Temp\

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.compiler=<NA>

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:os.name=Windows 7

 18:33:07.734 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:os.arch=amd64

 18:33:07.735 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:os.version=6.1

 18:33:07.735 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:user.name=qindongliang

 18:33:07.735 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:user.home=C:\Users\qindongliang

 18:33:07.735 [main] INFO  org.apache.zookeeper.ZooKeeper - Client environment:user.dir=D:\eclipseworkspace2yw\opzk

 18:33:07.735 [main] INFO  org.apache.zookeeper.ZooKeeper - Initiating client connection, connectString=192.168.46.22:2181 sessionTimeout=5000 watcher=org.apache.curator.ConnectionState@2c351b05

 18:33:07.738 [main] DEBUG org.apache.zookeeper.ClientCnxn - zookeeper.disableAutoWatchReset is false

 18:33:07.760 [main-SendThread(192.168.46.22:2181)] INFO  org.apache.zookeeper.ClientCnxn - Opening socket connection to server 192.168.46.22/192.168.46.22:2181. Will not attempt to authenticate using SASL (unknown error)

 18:33:07.761 [main-SendThread(192.168.46.22:2181)] INFO  org.apache.zookeeper.ClientCnxn - Socket connection established to 192.168.46.22/192.168.46.22:2181, initiating session

 18:33:07.762 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Session establishment request sent on 192.168.46.22/192.168.46.22:2181

 18:33:07.766 [main-SendThread(192.168.46.22:2181)] INFO  org.apache.zookeeper.ClientCnxn - Session establishment complete on server 192.168.46.22/192.168.46.22:2181, sessionid = 0x148ac15236f0046, negotiated timeout = 5000

 18:33:07.771 [main-EventThread] INFO  o.a.c.f.state.ConnectionStateManager - State change: CONNECTED

 18:33:08.784 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x148ac15236f0046, packet:: clientPath:null serverPath:null finished:false header:: 1,3  replyHeader:: 1,233,0  request:: '/php,F  response:: s{117,117,1411712541330,1411712541330,0,5,0,0,0,3,204}

 18:33:08.784 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Got ping response for sessionid: 0x148ac15236f0046 after 4ms

 监听开始/zk........

 18:33:08.795 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x148ac15236f0046, packet:: clientPath:null serverPath:null finished:false header:: 2,3  replyHeader:: 2,233,0  request:: '/php,F  response:: s{117,117,1411712541330,1411712541330,0,5,0,0,0,3,204}

 18:33:08.797 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x148ac15236f0046, packet:: clientPath:null serverPath:null finished:false header:: 3,3  replyHeader:: 3,233,0  request:: '/php/zk,F  response:: s{151,182,1411714954448,1411716422668,2,5,0,0,9,3,228}

 18:33:08.804 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x148ac15236f0046, packet:: clientPath:/php/zk serverPath:/php/zk finished:false header:: 4,12  replyHeader:: 4,233,0  request:: '/php/zk,T  response:: v{'bb,'cc,'cc334},s{151,182,1411714954448,1411716422668,2,5,0,0,9,3,228}

 18:33:08.815 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x148ac15236f0046, packet:: clientPath:/php/zk/bb serverPath:/php/zk/bb finished:false header:: 5,4  replyHeader:: 5,233,0  request:: '/php/zk/bb,T  response:: #6920616d2061207a6b20636f6e74656e742031,s{152,156,1411714954452,1411714982893,2,0,0,0,19,0,152}

 18:33:08.816 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x148ac15236f0046, packet:: clientPath:/php/zk/cc serverPath:/php/zk/cc finished:false header:: 6,4  replyHeader:: 6,233,0  request:: '/php/zk/cc,T  response:: #63313163,s{185,222,1411716737805,1411725726750,3,0,0,0,4,0,185}

 18:33:08.817 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Reading reply sessionid:0x148ac15236f0046, packet:: clientPath:/php/zk/cc334 serverPath:/php/zk/cc334 finished:false header:: 7,4  replyHeader:: 7,233,0  request:: '/php/zk/cc334,T  response:: #636363,s{189,226,1411716744253,1411725775109,2,3,0,0,3,3,220}

 Node added: bb

 Node added: cc

 Node added: cc334

 18:33:10.482 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Got ping response for sessionid: 0x148ac15236f0046 after 1ms

 18:33:12.148 [main-SendThread(192.168.46.22:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Got ping response for sessionid: 0x148ac15236f0046 after 1ms

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