ZK watcher 实现节点的监听

zk: localhost:2181(CONNECTED) 14] help
ZooKeeper -server host:port cmd args
        stat path [watch]
        set path data [version]
        ls path [watch]
        delquota [-n|-b] path
        ls2 path [watch]
        setAcl path acl
        setquota -n|-b val path
        history
        redo cmdno
        printwatches on|off
        delete path [version]
        sync path
        listquota path
        rmr path
        get path [watch]
        create [-s] [-e] path data acl
        addauth scheme auth
        quit
        getAcl path
        close
        connect host:port

监听器的原理：

watcher实现节点的监听

客户端A创建节点

[zk: localhost:2181(CONNECTED) 18] create /testwatcher 123
Created /testwatcher
[zk: localhost:2181(CONNECTED) 19] ls /
[controller_epoch, brokers, zookeeper, hellozk, testwatcher, admin, consumers, zktmp_1230000000021, config, my_zktmp0000000022, zktmp]

客户端B监听节点testwatch 变化 

[zk: 192.168.13.138(CONNECTED) 57] ls /
[controller_epoch, brokers, zookeeper, hellozk, testwatcher, admin, consumers, zktmp_1230000000021, config, my_zktmp0000000022, zktmp]
[zk: 192.168.13.138(CONNECTED) 58] get /testwatcher watch
123
cZxid = 0xd0000057a
ctime = Sun Mar 31 23:18:51 CST 2019
mZxid = 0xd0000057a
mtime = Sun Mar 31 23:18:51 CST 2019
pZxid = 0xd0000057a
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 3
numChildren = 0
[zk: 192.168.13.138(CONNECTED) 59]
WATCHER::

WatchedEvent state:SyncConnected type:NodeDataChanged path:/testwatcher

客户端A 重新set 修改数据

[zk: localhost:2181(CONNECTED) 20] set /testwatcher 456
cZxid = 0xd0000057a
ctime = Sun Mar 31 23:18:51 CST 2019
mZxid = 0xd0000057b
mtime = Sun Mar 31 23:19:36 CST 2019
pZxid = 0xd0000057a
cversion = 0
dataVersion = 1
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 3
numChildren = 0

客户端B收到了数据变化的监听

WatchedEvent state:SyncConnected type:NodeDataChanged path:/testwatcher

客户端A再次修改数据，客户端B不会再接受数据，因为watch机制是 只会监听一次变化，再次节点变化，则监听不到，只能再次设置监听任务

案例2：实现服务器变化，通知全部订阅节点的client

package com.itcast.zookeeper;

import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;

import java.io.IOException;
import java.util.List;

public class ZKClient2 {

    static ZooKeeper zk = null;

    public static void main(String[] args) throws KeeperException, InterruptedException, IOException {

        zk = new ZooKeeper("192.168.13.130:2181", 3000, new Watcher() {

            //客户端A再次修改数据，客户端B不会再接受数据，因为watch机制是 只会监听一次变化，再次节点变化，则监听不到，只能再次设置监听任务
            //比如/myGirls节点设置了一次beautiful的数据，

            /**
             * 监听到了数据
             * watchedEvent.getState()---SyncConnected
             * watchedEvent.getPath()----/myGirls
             * watchedEvent.getType()----NodeDataChanged
             *
             * 再次将myGirls节点设置成sexy将不会重复监听，徐涛再次设置监听任务
             */

            @Override
            public void process(WatchedEvent watchedEvent) {
                System.out.println("watchedEvent.getState()---" + watchedEvent.getState());
                System.out.println("watchedEvent.getPath()----" + watchedEvent.getPath());
                System.out.println("watchedEvent.getType()----" + watchedEvent.getType());

                if (watchedEvent.getType().equals(Event.EventType.NodeDataChanged)) {
                    try {
                    //true再次监听
                        byte[] data = zk.getData("/myGirls", true, null);
                        System.out.println("变更的数据是:" +new String(data));
                    } catch (KeeperException | InterruptedException e) {
                        e.printStackTrace();
                    }
                }

            }
        });

        //开启监听，数据有变化，则出发客户端监听回调
        zk.getData("/myGirls",true,null);
        Thread.sleep(Integer.MAX_VALUE);
        zk.close();


    }

}

修改节点数据

set /myGirls 7777777778890000

发现Client监听到了变化的数据