【Zookeeper】服务器动态上下线监听案例

 学习视频 

【尚硅谷】2021新版Zookeeper 3.5.7版本教程

集数：20—23

 学习笔记 

【Java】学习笔记汇总

• 一、需求分析
• 二、具体实现
• • 2.1 代码
  • 2.2 测试

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。

步骤1：先在集群上创建/servers节点

create /servers "servers"

步骤2：编写模拟分布式服务器端代码

public class DistributeServer {

    private String connectString = "192.168.150.101:2181";
    private int sessionTimeout = 10000;
    private ZooKeeper zooKeeper;

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        DistributeServer server = new DistributeServer();
        // 1 获取zk连接
        server.getConnect();
        // 2 注册服务器到zk集群
        server.regist(args[0]);
        // 3 启动业务逻辑（睡觉）
        server.businesss();
    }

    private void businesss() throws InterruptedException {
        Thread.sleep(Long.MAX_VALUE);
    }

    private void regist(String hostname) throws InterruptedException, KeeperException {
        String create = zooKeeper.create("/servers/" + hostname, hostname.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        System.out.println(hostname + " is online!");
    }

    private void getConnect() throws IOException {
        zooKeeper = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {

            }
        });
    }
}

步骤3：编写模拟分布式客户端代码

public class DistributeClient {

    private String connectString = "192.168.150.101:2181";
    private int sessionTimeout = 10000;
    private ZooKeeper zooKeeper;

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        DistributeClient client = new DistributeClient();

        // 1 获取连接
        client.getConnect();
        // 2 监听/servers下面子节点的增加和删除
        client.getServerList();
        // 3 业务逻辑（睡觉）
        client.businesss();
    }

    private void getServerList() throws InterruptedException, KeeperException {
        List children = zooKeeper.getChildren("/servers", true);
        ArrayList servers = new ArrayList<>();
        for (String child : children) {
            byte[] data = zooKeeper.getData("/servers/" + child, false, null);
            servers.add(new String(data));
        }
        System.out.println(servers);
    }

    private void businesss() throws InterruptedException {
        Thread.sleep(Long.MAX_VALUE);
    }
    

    private void getConnect() throws IOException {
        zooKeeper = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                // 调用getServerList，可以保证持续监听
                try {
                    getServerList();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (KeeperException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

步骤1：运行客户端代码DistributeClient

步骤2：启动zk服务器的命令行，测试客户端能否监控到zk节点的变化

zk命令行：

[zk: localhost:2181(CONNECTED) 11] create /servers/server1 "server1"
Created /servers/server1
[zk: localhost:2181(CONNECTED) 12] create /servers/server2 "server2"
Created /servers/server2

Idea运行的客户端输出

# 运行时输出
[]
[]
# create /servers/server1 "server1" 后输出
[server1]
# create /servers/server2 "server2" 后输出
[server2, server1]

可证明客户端代码没问题。

步骤3：带参数运行模拟的服务端程序

首先要设置参数

此时运行代码。

模拟的服务端控制台打印：

server3 is online!

模拟的客户端控制台打印：

[server3, server2, server1]