Zookeeeper开源客户端curator watcherAPI的使用

一、概述

二、监听单个节点变化

三、监听子节点变化

四、总结

一、概述

curator提供了两种Watcher(Cache)来监听结点的变化。

Node Cache : 只是监听某一个特定的节点，监听节点的新增和修改；
PathChildren Cache : 监控一个ZNode的子节点. 当一个子节点增加，更新，删除时， Path Cache会改变它的状态，会包含最新的子节点，子节点的数据和状态；

二、监听单个节点变化

如果我们需要监听单个节点变化，可以使用NodeCache对象。

NodeCache(CuratorFramework client, String path)

参数说明：

client: curator客户端连接对象；
path: 需要监听的节点路径；

package com.wsh.zookeeper.zookeeperapidemo.curator;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.slf4j.Logger;
import org.slf4j.LoggerFactory;public class CuratorWatcherAPI {private static final Logger logger = LoggerFactory.getLogger(CuratorWatcherAPI.class);private static final String ZOOKEEPER_SERVER_ADDRESS = "192.168.179.128:2181,192.168.179.129:2181,192.168.179.133:2181";/*** Curator对象*/private static CuratorFramework curatorFramework;static {//初始化curator对象curatorFramework = CuratorFrameworkFactory.builder()//会话超时时间.sessionTimeoutMs(5000)//服务器集群地址.connectString(ZOOKEEPER_SERVER_ADDRESS)//重试策略.retryPolicy(new ExponentialBackoffRetry(1000, 3))//命名空间.namespace("watcher").build();//开启客户端curatorFramework.start();}/*** 1. 监控单个节点变化* NodeCache(CuratorFramework client, String path)* client: curator客户端连接对象* path: 需要监听的节点路径*/public void watchOneNode() throws Exception {NodeCache nodeCache = new NodeCache(curatorFramework, "/watcher1");//启动监视器nodeCache.start();nodeCache.getListenable().addListener(new NodeCacheListener() {@Overridepublic void nodeChanged() throws Exception {logger.info("节点路径：" + nodeCache.getCurrentData().getPath());logger.info("节点数据：" + new String(nodeCache.getCurrentData().getData()));}});Thread.sleep(50000);//关闭监视器nodeCache.close();}public static void main(String[] args) throws Exception {CuratorWatcherAPI curatorWatcherAPI = new CuratorWatcherAPI();curatorWatcherAPI.watchOneNode();}}

启动程序，使用zkCli.sh连接到zookeeper集群，使用下面的命令创建两个节点：

[zk: localhost:2181(CONNECTED) 38] create /watcher "watcher"
Created /watcher
[zk: localhost:2181(CONNECTED) 39] create /watcher/watcher1 "watcher1"
Created /watcher/watcher1

观察后端日志：

14:00:21.493 [main-EventThread] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点路径：/watcher1
14:00:21.493 [main-EventThread] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点数据：watcher1114:00:25.321 [main-EventThread] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点路径：/watcher1
14:00:25.321 [main-EventThread] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点数据：watcher111

可以看到，curator监听到了节点的变化事件，并且这个监听是可以重复进行监听的。

三、监听子节点变化

如果我们需要监听子节点的变化，可以通过构造PathChildrenCache对象实现。

PathChildrenCache(CuratorFramework client, String path, boolean cacheData)

参数说明：

client: curator客户端连接对象；
path: 监听节点路径；
cacheData: 监听事件中是否获取节点数据；

package com.wsh.zookeeper.zookeeperapidemo.curator;import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.cache.*;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;public class CuratorWatcherAPI {private static final Logger logger = LoggerFactory.getLogger(CuratorWatcherAPI.class);private static final String ZOOKEEPER_SERVER_ADDRESS = "192.168.179.128:2181,192.168.179.129:2181,192.168.179.133:2181";/*** Curator对象*/private static CuratorFramework curatorFramework;static {//初始化curator对象curatorFramework = CuratorFrameworkFactory.builder()//会话超时时间.sessionTimeoutMs(5000)//服务器集群地址.connectString(ZOOKEEPER_SERVER_ADDRESS)//重试策略.retryPolicy(new ExponentialBackoffRetry(1000, 3))//命名空间.namespace("watcher").build();//开启客户端curatorFramework.start();}/*** 2. 监听子节点数据变化* PathChildrenCache(CuratorFramework client, String path, boolean cacheData)* client: curator客户端连接对象* path: 监听节点路径* cacheData: 监听事件中是否获取节点数据*/public void watchChildrenNode() throws Exception {PathChildrenCache pathChildrenCache = new PathChildrenCache(curatorFramework, "watcher1", true);//启动监听器pathChildrenCache.start();pathChildrenCache.getListenable().addListener(new PathChildrenCacheListener() {@Overridepublic void childEvent(CuratorFramework curatorFramework, PathChildrenCacheEvent pathChildrenCacheEvent) throws Exception {logger.info("事件类型：" + pathChildrenCacheEvent.getType());logger.info("节点路径：" + new String(pathChildrenCacheEvent.getData().getPath()));logger.info("节点数据：" + new String(pathChildrenCacheEvent.getData().getData()));}});Thread.sleep(50000);//关闭监听器pathChildrenCache.close();}public static void main(String[] args) throws Exception {CuratorWatcherAPI curatorWatcherAPI = new CuratorWatcherAPI();curatorWatcherAPI.watchChildrenNode();}}

使用客户端操作节点：

[zk: localhost:2181(CONNECTED) 42] create /watcher/watcher1/node1 "node1"
Created /watcher/watcher1/node1
[zk: localhost:2181(CONNECTED) 43] create /watcher/watcher1/node2 "node2"
Created /watcher/watcher1/node2
[zk: localhost:2181(CONNECTED) 44] set /watcher/watcher1/node1 "node11"
cZxid = 0x500000050
ctime = Tue Dec 29 14:06:31 CST 2020
mZxid = 0x500000052
mtime = Tue Dec 29 14:06:45 CST 2020
pZxid = 0x500000050
cversion = 0
dataVersion = 1
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 6
numChildren = 0
[zk: localhost:2181(CONNECTED) 45] delete /watcher/watcher1/node1

观察后台日志：

14:06:31.361 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 事件类型：CHILD_ADDED
14:06:31.361 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点路径：/watcher1/node1
14:06:31.361 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点数据：node114:06:36.130 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 事件类型：CHILD_ADDED
14:06:36.130 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点路径：/watcher1/node2
14:06:36.130 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点数据：node214:06:45.091 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 事件类型：CHILD_UPDATED
14:06:45.091 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点路径：/watcher1/node1
14:06:45.091 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点数据：node1114:06:55.539 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 事件类型：CHILD_REMOVED
14:06:55.539 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点路径：/watcher1/node1
14:06:55.539 [PathChildrenCache-0] INFO com.wsh.zookeeper.zookeeperapidemo.curator.CuratorWatcherAPI - 节点数据：node11

如上，可以看到，curator监听到了子节点的变化事件，并且这个监听也是可以重复进行监听的。

四、总结

本篇文章主要总结curator中监听事件API的使用方法，在实际工作中，监听机制很有用，可以使用在分布式配置的动态感知等场景。

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Zookeeeper开源客户端curator watcherAPI的使用

一、概述

二、监听单个节点变化

三、监听子节点变化

四、总结

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