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。

需求分析

具体实现

1. 先在集群上创建/servers节点

   [zk: localhost:2181(CONNECTED) 7] create /servers "servers"
   Created /servers

2. 在Idea中创建包名：com.zh.zhcase1

3. 服务器端向Zookeeper注册代码 ```java package com.zh.zkcase1;

import org.apache.zookeeper.*;

import java.io.IOException;

/**

• author: zhanghui
• project: big-data-learning
• package: com.zh.zkcase1
• filename: DistributeServer
• date: 2022/2/28 14:29

• description: 服务器端向Zookeeper注册 */ public class DistributeServer { private static String connectString = “linux102:2181,linux103:2181,linux104:2181”; private static int sessionTimeout = 2000; private ZooKeeper zk = null; private String parentNode = “/servers”;

  // 创建到zk的客户端连接 public void getConnect() throws IOException {

   zk = new ZooKeeper(connectString, sessionTimeout, event -> System.out.println(event.getType() + "---" + event.getPath()));
  

  }

  // 注册服务器 public void registerServer(String hostname) throws Exception {

   String create = zk.create(parentNode + "/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...");
   Thread.sleep(Long.MAX_VALUE);
  

  }

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

   // 1. 获取Zk连接
   DistributeServer server = new DistributeServer();
   server.getConnect();
  
   // 2. 利用Zk连接注册服务器信息
   server.registerServer(args[0]);
  
   // 3. 启动业务功能
   server.business(args[0]);
  

  } } ```

1. 客户端代码 ```java package com.zh.zkcase1;

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

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

/**

• author: zhanghui
• project: big-data-learning
• package: com.zh.zkcase1
• filename: DistributeClient
• date: 2022/2/28 14:50

• description: zk客户端 */ public class DistributeClient { private static String connectString = “linux102:2181,linux103:2181,linux104:2181”; private static int sessionTimeout = 2000; private ZooKeeper zk = null; private String parentNode = “/servers”;

  // 创建到zk的客户端连接 public void getConnect() throws IOException {

   new ZooKeeper(connectString, sessionTimeout, event -> {
       System.out.println(event.getType() + "---" + event.getPath());
  
       // 再次启动监听
       try {
           getServerList();
       } catch (Exception e) {
           e.printStackTrace();
       }
   });
  

  }

  // 获取服务器列表信息 public void getServerList() throws Exception {

   // 1. 获取服务器子节点信息，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 Exception {

   System.out.println("client is working...");
   Thread.sleep(Long.MAX_VALUE);
  

  }

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

   // 1. 获取ZK连接
   DistributeClient client = new DistributeClient();
   client.getConnect();
  
   // 2. 获取servers的子节点信息，从中获取服务器信息列表
   client.getServerList();
  
   // 3. 业务进程启动
   client.business();
  

  } } ```

测试

1. 在linux命令行上操作增加减少服务器

   1. 启动DistributeClient客户端

   2. 在linux102上ZK的客户端/servers目录上创建临时带序号节点

      [zk: localhost:2181(CONNECTED) 8] create -e -s /servers/linux102 "linux102"
      Created /servers/linux1020000000000
      [zk: localhost:2181(CONNECTED) 9] create -e -s /servers/linux103 "linux103"
      Created /servers/linux1030000000001
      

   3. 观察idea控制台

      NodeChildrenChanged---/servers
      [linux102, linux103]
      

   4. 执行删除操作

      [zk: localhost:2181(CONNECTED) 10] delete /servers/linux1020000000000
      

   5. 观察idea控制台变化

      NodeChildrenChanged---/servers
      [linux103]
      

2. 在IDEA上操作增加减少服务器

   1. 启动DistributeClient客户端（如果已经启动过，不需要启动）
   2. 启动DistributeServer服务
      1. 点击Edit Configurations…

  2. 在弹出的窗口中（Program arguments）输入想启动的主机，例如，linux102

  3. 回到DistributeServer的main方法，右键，在弹出的窗口中点击`Run "DistributeServer.main()"`

  4. 观察DistributeServer控制台，提示`linux102 is working...`
  4. 观察DistributeClient控制台，提示`[linux102, linux103]`