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。其实本质就是节点的创建和移除。

具体实现

1、先在集群上创建/servers 节点

2、编写服务端java代码

package dynamicSartedAndStop; import org.apache.zookeeper.*; import java.io.IOException;  public class DistributeServer { private static String connectString = "192.168.80.18:2181,192.168.80.19:2181,192.168.80.20:2181"; private static int sessionTimeout = 200000; private ZooKeeper zk = null; private String parentNode = "/servers";  public void getConnect() throws IOException { zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() { public void process(WatchedEvent watchedEvent) { } }); }  public void registServer(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); }  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 {  DistributeServer server = new DistributeServer(); server.getConnect();  server.registServer(args[0]);  server.business(args[0]); } }

3、编写客户端java代码

package dynamicSartedAndStop; 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;  public class DistributeClient { private static String connectString = "192.168.80.18:2181,192.168.80.19:2181,192.168.80.20:2181";  private static int sessionTimeout = 200000; private ZooKeeper zk = null; private String parentNode = "/servers";  public void getConnect() throws IOException { zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() { public void process(WatchedEvent event) {  try { getServerList(); } catch (Exception e) { e.printStackTrace(); } } }); }  public void getServerList() throws Exception {  List<String> children = zk.getChildren(parentNode, true);  ArrayList<String> servers = new ArrayList<>();  for (String child : children) { byte[] data = zk.getData(parentNode + "/" + child, false, null); servers.add(new String(data)); }  System.out.println(servers); }  public void business() throws Exception { 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(); } }