ZooKeeper(3.4.5)

ZooKeeper原生的API支持通过注册Watcher来进行事件监听，但是Watcher通知是一次性的，因此开发过程中需要反复注册Watcher，比较繁琐。Curator引入了Cache来监听ZooKeeper服务端的事件。Cache对ZooKeeper事件监听进行了封装，能够自动处理反复注册监听，简化了ZooKeeper原生API繁琐的开发过程。
简单的示例：
 1 package com.huey.dream.demo;
 2 
 3 import java.util.concurrent.ExecutorService;
 4 import java.util.concurrent.Executors;
 5 
 6 import org.apache.curator.framework.CuratorFramework;
 7 import org.apache.curator.framework.CuratorFrameworkFactory;
 8 import org.apache.curator.framework.recipes.cache.NodeCache;
 9 import org.apache.curator.framework.recipes.cache.NodeCacheListener;
10 import org.apache.curator.framework.recipes.cache.PathChildrenCache;
11 import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent;
12 import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener;
13 import org.apache.curator.framework.recipes.cache.PathChildrenCache.StartMode;
14 import org.apache.curator.retry.ExponentialBackoffRetry;
15 
16 /**
17  * Curator事件监听
18  * @author  huey
19  * @version 1.0 
20  * @created 2015-3-2
21  */
22 public class CarutorDemo {
23 
24     public static void main(String[] args) throws Exception {
25         CuratorFramework client = CuratorFrameworkFactory.builder()
26             .connectString("192.168.1.109:2181")
27             .sessionTimeoutMs(5000)
28             .connectionTimeoutMs(3000)
29             .retryPolicy(new ExponentialBackoffRetry(1000, 3))
30             .build();
31         client.start();
32         
33         client.create()
34             .creatingParentsIfNeeded()
35             .forPath("/zk-huey/cnode", "hello".getBytes());
36         
37         /**
38          * 在注册监听器的时候，如果传入此参数，当事件触发时，逻辑由线程池处理
39          */
40         ExecutorService pool = Executors.newFixedThreadPool(2);
41         
42         /**
43          * 监听数据节点的变化情况
44          */
45         final NodeCache nodeCache = new NodeCache(client, "/zk-huey/cnode", false);
46         nodeCache.start(true);
47         nodeCache.getListenable().addListener(
48             new NodeCacheListener() {
49                 @Override
50                 public void nodeChanged() throws Exception {
51                     System.out.println("Node data is changed, new data: " + 
52                         new String(nodeCache.getCurrentData().getData()));
53                 }
54             }, 
55             pool
56         );
57         
58         /**
59          * 监听子节点的变化情况
60          */
61         final PathChildrenCache childrenCache = new PathChildrenCache(client, "/zk-huey", true);
62         childrenCache.start(StartMode.POST_INITIALIZED_EVENT);
63         childrenCache.getListenable().addListener(
64             new PathChildrenCacheListener() {
65                 @Override
66                 public void childEvent(CuratorFramework client, PathChildrenCacheEvent event)
67                         throws Exception {
68                         switch (event.getType()) {
69                         case CHILD_ADDED:
70                             System.out.println("CHILD_ADDED: " + event.getData().getPath());
71                             break;
72                         case CHILD_REMOVED:
73                             System.out.println("CHILD_REMOVED: " + event.getData().getPath());
74                             break;
75                         case CHILD_UPDATED:
76                             System.out.println("CHILD_UPDATED: " + event.getData().getPath());
77                             break;
78                         default:
79                             break;
80                     }
81                 }
82             },
83             pool
84         );
85         
86         client.setData().forPath("/zk-huey/cnode", "world".getBytes());
87         
88         Thread.sleep(10 * 1000);
89         pool.shutdown();
90         client.close();
91     }
92 }