Zookeeper框架Curator之事件监听-yellowcong

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Curator通过NodeCache、PathChildrenCache、TreeCache 对节点变化进行监听操作，以前的Zookeeper的Wacher效果差，而Curator的做法是以牺牲内存的方法来换取效率，通过NodeCache的方法，监听缓存的数据，比较缓存数据和Zookeeper服务器数据，来判断事件

1.Curator Cache 与原生ZooKeeper Wacher区别

原生的ZooKeeper Wacher是一次性的：一个Wacher一旦触发就会被移出，如果你想要反复使用Wacher，就要在Wacher被移除后重新注册，使用起来很麻烦。使用Curator Cache 可以反复使用Wacher了。

2.Curator Cache 和Curator Wacher区别

2.相关类

Curator Cache主要提供了一下三组类，分别用于实现对节点的监听，子节点的监听和二者的混合：

1.NodeCache,NodeCacheListener，ChildData，节点创建，节点数据内容变更，不能监听节点删除。

2.PathChildrenCache，PathChildrenCacheListener，PathChildrenCacheEvent监听指定节点的子节点的变更包括添加，删除，子节点数据数据变更这三类。这个监听用得多

3.TreeCache，TreeCacheListener，TreeCacheEvent，TreeCacheSelector

NodeCacheListener案例

这个节点监听操作，不会监听删除事件，而且这种监听操作用到的场景很少

package com.yellowcong.zookeeper.curator;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import org.apache.curator.RetryPolicy;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.cache.ChildData;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;/** * 创建日期:2017年10月14日 <br/> * 创建用户:yellowcong <br/> * 功能描述:   */public class CuratorWatcherDemo {    private static final String CONNECT_PATH = "192.168.66.110:2181,192.168.66.110:2182,192.168.66.110:2183";    // Session 超时时间    private static final int SESSION_TIME_OUT = 60000;    //连接超时    private static final int CONNECT_TIME_OUT = 5000;    public static void main(String[] args) throws Exception {        //1、尝试策略        RetryPolicy retryPolicy = new ExponentialBackoffRetry(5000, 10);        //2、创建CuratorFramework 工厂类        CuratorFramework cf = CuratorFrameworkFactory.builder()            .connectString(CONNECT_PATH)            .connectionTimeoutMs(SESSION_TIME_OUT)            .sessionTimeoutMs(CONNECT_TIME_OUT)            .retryPolicy(retryPolicy)            .build();        //3、启动连接        cf.start();        //4、建立一个Cache缓存        final NodeCache cache = new NodeCache(cf, "/curator/nodecache",false);        cache.start();        ExecutorService pool = Executors.newCachedThreadPool();        //创建监听器        cache.getListenable().addListener(new NodeCacheListener() {            public void nodeChanged() throws Exception {                ChildData data = cache.getCurrentData();                System.out.println("修改路径\t"+data.getPath());                System.out.println("数据类容\t"+new String(data.getData()));                System.out.println("状态\t"+data.getStat());                System.out.println("-------------------------");            }        },pool);        //创建节点        Thread.sleep(1000);        cf.create().withMode(CreateMode.PERSISTENT).forPath("/curator/nodecache","nodecache  test".getBytes());        //数据修改        Thread.sleep(1000);        cf.setData().forPath("/curator/nodecache","update".getBytes());        //获取节点数据        Thread.sleep(1000);        byte [] data = cf.getData().forPath("/curator/nodecache");        System.out.println(new String(data));        //删除节点        cf.delete().deletingChildrenIfNeeded().forPath("/curator/nodecache");    }}

PathChildrenCacheListener 案例

PathChildrenCache.StartMode
• BUILD_INITIAL_CACHE //同步初始化客户端的cache，及创建cache后，就从服务器端拉入对应的数据(这个是NodeCache使用的方式)
• NORMAL //异步初始化cache
•POST_INITIALIZED_EVENT //异步初始化，初始化完成触发事件PathChildrenCacheEvent.Type.INITIALIZED (这个方式是 PathChildrenCacheListener 使用的)

dataIsCompressed 是否进行数据压缩，如果设定为false，如果在节点修改了数据，就不会直接存在缓存中，需要自己重新取一遍，一般设置为true

package com.yellowcong.zookeeper.curator;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import org.apache.curator.RetryPolicy;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.cache.ChildData;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.framework.recipes.cache.PathChildrenCache.StartMode;import org.apache.curator.retry.ExponentialBackoffRetry;import org.apache.zookeeper.CreateMode;import org.apache.zookeeper.data.Stat;/** * 创建日期:2017年10月14日 <br/> * 创建用户:yellowcong <br/> * 功能描述:   */public class CuratorWatcherDemo2 {    private static final String CONNECT_PATH = "192.168.66.110:2181,192.168.66.110:2182,192.168.66.110:2183";    // Session 超时时间    private static final int SESSION_TIME_OUT = 60000;    //连接超时    private static final int CONNECT_TIME_OUT = 5000;    public static void main(String[] args) throws Exception {        //1、尝试策略        RetryPolicy retryPolicy = new ExponentialBackoffRetry(5000, 10);        //2、创建CuratorFramework 工厂类        CuratorFramework cf = CuratorFrameworkFactory.builder()            .connectString(CONNECT_PATH)            .connectionTimeoutMs(SESSION_TIME_OUT)            .sessionTimeoutMs(CONNECT_TIME_OUT)            .retryPolicy(retryPolicy)            .build();        //3、启动连接        cf.start();        //4、建立一个Cache缓存 ,第三个参数是 dataIsCompressed 是否进行数据压缩  ,需要配置为true        //如果第三个参数设置为 false,则不接受节点变更后的数据        final PathChildrenCache cache = new PathChildrenCache(cf, "/curator", true);        //5、设定监听的模式 ,异步初始化，初始化完成触发事件 PathChildrenCacheEvent.Type.INITIALIZED        cache.start(StartMode.POST_INITIALIZED_EVENT);        ExecutorService pool = Executors.newCachedThreadPool();        //创建监听器        cache.getListenable().addListener(new PathChildrenCacheListener() {            public void childEvent(CuratorFramework cf, PathChildrenCacheEvent event) throws Exception {                // TODO Auto-generated method stub                ChildData data = event.getData();                System.out.println("路径\t"+data.getPath());                System.out.println("更改数据\t"+new String(data.getData()));                System.out.println("节点状态\t"+data.getStat());                System.out.println(event.getType());                switch (event.getType()) {                //初始化会触发这个事件                case INITIALIZED:                    System.out.println("子类缓存系统初始化完成");                    break;                case CHILD_ADDED:                    System.out.println("添加子节点");                    break;                case CHILD_UPDATED:                    System.out.println("更新子节点");                    break;                case CHILD_REMOVED:                    System.out.println("删除子节点");                    break;                default:                    break;                }                System.out.println("----------------------------------");            }        });        //判断节点是否存在，然后删除掉        Stat stat = cf.checkExists().forPath("/curator/nodecache2");        if(stat != null){            Thread.sleep(1000);            cf.delete().deletingChildrenIfNeeded().forPath("/curator/nodecache2");        }        //创建节点        Thread.sleep(1000);        cf.create().withMode(CreateMode.PERSISTENT).forPath("/curator/nodecache2","nodecache  test".getBytes());        //数据修改        Thread.sleep(1000);        cf.setData().forPath("/curator/nodecache2","update".getBytes());        //获取节点数据        Thread.sleep(1000);        byte [] data = cf.getData().forPath("/curator/nodecache2");        System.out.println(new String(data));        //删除节点        Thread.sleep(1000);        cf.delete().deletingChildrenIfNeeded().forPath("/curator/nodecache2");    }}

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