服务器动态上下线监听案例

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。

代码实现

服务端代码

package com.atguigu.zkcase1;
import java.io.IOException;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.ZooDefs.Ids;
public class DistributeServer {
 private static String connectString = 
"hadoop102:2181,hadoop103:2181,hadoop104:2181";
 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, new 
Watcher() {
        @Override
        public void process(WatchedEvent event) {
          }
        });
  }

// 注册服务器
 public void registServer(String hostname) throws Exception{
 
    String create = zk.create(parentNode + "/server", 
hostname.getBytes(), 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.registServer(args[0]);

// 3 启动业务功能
    server.business(args[0]);
    }
 }

客户端代码

package com.atguigu.zkcase1;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

public class DistributeClient {
 
 private static String connectString = 
"hadoop102:2181,hadoop103:2181,hadoop104:2181";
 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, new 
Watcher() {
 
       @Override
       public void process(WatchedEvent event) {

          // 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();
  }
}