需求

某分布式系统中，主节点可以有多台，可以动态上下线，任意一台客户端都能实时感知到主节点服务器的上下线。
思路

思路

   1. 创建客户端与服务端
   2.启动client端 监听
   3. 启动server端 注册
   4.当server端 发生上下线
   5.client端都能感知到

实现步骤

1.在shell命令客户端创建 servers (方便连接)

 create /servers "servers"

创建两个自定义类

自定义DistrbuteServer（服务器端代码块）

package com.zookeeper.servers;

import org.apache.xerces.dom.ParentNode;
import org.apache.zookeeper.*;

import java.io.IOException;
import java.util.Scanner;

/**
 * @version v1.0
 * @Author: huang*
 * @Date: 2020/12/16*
 */
public class DistrbuteServer {
    private static String connectString="bigdata01:2181,bigdata02:2181,bigdata03:2181";
    private static int sessionTimeout=2000;
    private ZooKeeper zk=null;
    private String partentNode ="/servers";

    //创建zk的客户端连接
    public  void getConnect() throws IOException {
         zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
                    System.out.println("servers端连接成功");
                }
            }
        });
    }

     //注册服务器（创建一个临时序列节点）
    //
    public void registServer(String hostname) throws Exception{
        String create = zk.create(partentNode + "/server", hostname.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        System.out.println(hostname+"is online"+ create);
    }

   //业务功能
    public void business(String hostname) throws Exception{
        System.out.println(hostname+"is working,,,,");
            //保证线程不结束
           Thread.sleep(Long.MAX_VALUE);
    }

    public static void main(String[] args) throws Exception {
        System.out.println("请输入服务器的名字");
        String hostname = new Scanner(System.in).next();

         //1.获取zk连接
        DistrbuteServer server = new DistrbuteServer();
        server.getConnect();
         //2.利用zk连接注册服务器信息
        server.registServer(hostname);
        //3.启动业务功能
        server.business(hostname);

    }

}

自定义 DistributeClient（客户端代码）

package com.zookeeper.servers;


import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.ipc.Client;
import org.apache.hadoop.mapreduce.tools.CLI;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

import java.util.ArrayList;
import java.util.List;

/**
 * @version v1.0
 * @Author: huang*
 * @Date: 2020/12/16*
 */
public class DistributeClient {
    private  static String connectString="bigdata01:2181,bigdata02:2181,bigdata03:2181";
    private static  int sessionTimeout=20000;
    private ZooKeeper zk=null;
    private String parentNode="/servers";

    //创建zk客户端连接
    public  void getConnect()throws Exception{
        zk=new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                if (watchedEvent.getState()==Event.KeeperState.SyncConnected) {
                    System.out.println("client 客户端连接成功!");
                }
                    //再一次启动监听
                    try {
                        getServerList();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }

        });
    }

     //获取服务器列表信息
    public  void getServerList() throws KeeperException, InterruptedException {
        //1.获取服务器节点信息，并且对父节点进行监听
        List<String> children = zk.getChildren(parentNode, true);
         //2.存储服务器信息列表
        ArrayList<String> servers = new ArrayList<>();
        //3.遍历所有节点，获取节点中的主机名称信息
        for (String child : children) {
            byte[] data = zk.getData(parentNode + "/" + child, false, null);
            servers.add(new String(data));
            //4.打印服务器列表信息
            System.out.println(servers);

        }

        //业务功能


    }

    public void business() throws InterruptedException {
        System.out.println("client is working,,,");
        Thread.sleep(Long.MAX_VALUE);
    }

    public static void main(String[] args) throws Exception {
        DistributeClient client
                = new DistributeClient();
        client.getConnect();
        client.getServerList();
        client.business();
    }

}

测试

shell命令行创建节点

客户端查看测试

server 节点查看测试