1、Code -> GitHub

https://github.com/liufengji/zookeeper_code.git

2、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

3、需求分析

4、先在集群上创建/servers节点

[zk: localhost:2181(CONNECTED) 10] create /servers "servers"

5、服务器端代码

import java.io.IOException;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.ZooDefs.Ids;

public class ZKServer {

    private String connectString = "node1:2181,node2:2181,node3:2181";
    private int sessionTimeout = 2000;
    private String parentNode = "/servers";
    ZooKeeper zkClient;

    // 建立连接
    public void getConnection() throws IOException {
        zkClient = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent event) { }
        });
    }

    // 业务
    public void business() throws InterruptedException{
        System.out.println("添加节点了…");
        Thread.sleep(Long.MAX_VALUE);
    }
    
    // 注册
    public void regist(String hostname) throws KeeperException, InterruptedException {
        String create = zkClient.create(parentNode + "/server",
                                     hostname.getBytes(),
 Ids.OPEN_ACL_UNSAFE,
                   CreateMode.EPHEMERAL_SEQUENTIAL);

        System.out.println(hostname + " is online " + create);
    }

    public static void main(String[] args) throws Exception {

        ZKServer zkServer = new ZKServer();
        // 1 建立连接
        zkServer.getConnection();

        // 2 注册
        zkServer.regist(args[0]);

        // 3 具体业务处理
        zkServer.business();
    }
}

6、客户端代码

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

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

public class ZKClient {

    private String connectString = "node1:2181,node2:2181,node3:2181";
    private int sessionTimeout = 2000;
    ZooKeeper zkClient;
    private String parentNode = "/servers";
    
    // 获取连接
    public void getConnect() throws IOException {
        zkClient = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent event) { 
                try {
                    getServersList();
                } catch (KeeperException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
    }

    // 监听节点变化
    public void getServersList() throws KeeperException, InterruptedException{
        List<String> children = zkClient.getChildren(parentNode, true);
        ArrayList<String> servers = new ArrayList<>();
        for (String node : children) {
            byte[] data = zkClient.getData(parentNode+"/"+node, false, null);
            servers.add(new String(data));
        }
        System.out.println(servers);
    }
    
    
    // 业务
    public void business() throws InterruptedException{
        System.out.println("节点状态"); 
        Thread.sleep(Long.MAX_VALUE);
    }
    
    public static void main(String[] args) throws Exception {

        ZKClient zk = new ZKClient();
        
        // 1 获取连接
        zk.getConnect();
        
        // 2 监听节点变化
        zk.getServersList();

        // 3 业务逻辑处理
        zk.business();
        
    }
}