ZooKeeper是一个分布式协调服务，它可以用于实现服务发现。以下是使用ZooKeeper实现服务发现的步骤：

1. 安装和配置ZooKeeper

首先，你需要安装和配置ZooKeeper集群。确保ZooKeeper集群正常运行并且各个节点之间可以通信。

2. 创建服务注册节点

在ZooKeeper中创建一个用于存储服务信息的节点。通常，这个节点会放在一个特定的路径下，例如 /services。

create /services/my-service ""

3. 服务注册

当一个服务启动时，它会在ZooKeeper中创建一个临时节点来注册自己。这个节点可以包含服务的地址、端口等信息。

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;

public class ServiceRegistry {
    private static final String ZK_ADDRESS = "localhost:2181";
    private static final int SESSION_TIMEOUT = 3000;
    private static final String SERVICES_PATH = "/services";
    private static final String SERVICE_NAME = "my-service";

    public static void main(String[] args) throws Exception {
        ZooKeeper zk = new ZooKeeper(ZK_ADDRESS, SESSION_TIMEOUT, event -> {
            // 处理连接事件
        });

        String servicePath = SERVICES_PATH + "/" + SERVICE_NAME;
        if (zk.exists(servicePath, false) == null) {
            zk.create(servicePath, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        }

        // 注册服务信息
        String serviceInfo = "http://localhost:8080";
        zk.create(servicePath + "/instance", serviceInfo.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);

        // 关闭ZooKeeper连接
        zk.close();
    }
}

4. 服务发现

其他服务可以通过查询ZooKeeper来发现可用的服务实例。

import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;

import java.util.List;

public class ServiceDiscovery {
    private static final String ZK_ADDRESS = "localhost:2181";
    private static final int SESSION_TIMEOUT = 3000;
    private static final String SERVICES_PATH = "/services";
    private static final String SERVICE_NAME = "my-service";

    public static void main(String[] args) throws Exception {
        ZooKeeper zk = new ZooKeeper(ZK_ADDRESS, SESSION_TIMEOUT, event -> {
            // 处理连接事件
        });

        String servicePath = SERVICES_PATH + "/" + SERVICE_NAME;
        if (zk.exists(servicePath, false) != null) {
            List instances = zk.getChildren(servicePath, false);
            for (String instance : instances) {
                byte[] data = zk.getData(servicePath + "/" + instance, false, new Stat());
                System.out.println("Service instance: " + new String(data));
            }
        }

        // 关闭ZooKeeper连接
        zk.close();
    }
}

5. 监听服务变化

为了实时获取服务实例的变化，可以使用ZooKeeper的监听机制。

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

public class ServiceChangeListener implements Watcher {
    private static final String ZK_ADDRESS = "localhost:2181";
    private static final int SESSION_TIMEOUT = 3000;
    private static final String SERVICES_PATH = "/services";
    private static final String SERVICE_NAME = "my-service";

    private ZooKeeper zk;

    public ServiceChangeListener() throws Exception {
        zk = new ZooKeeper(ZK_ADDRESS, SESSION_TIMEOUT, this);
    }

    @Override
    public void process(WatchedEvent event) {
        if (event.getType() == Event.EventType.NodeChildrenChanged) {
            try {
                String servicePath = SERVICES_PATH + "/" + SERVICE_NAME;
                List instances = zk.getChildren(servicePath, this);
                for (String instance : instances) {
                    byte[] data = zk.getData(servicePath + "/" + instance, false, new Stat());
                    System.out.println("Service instance changed: " + new String(data));
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) throws Exception {
        new ServiceChangeListener();
        // 保持程序运行
        Thread.sleep(Long.MAX_VALUE);
    }
}

总结

通过以上步骤，你可以使用ZooKeeper实现服务发现。服务注册时会在ZooKeeper中创建临时节点，服务发现时查询这些节点并监听其变化。这样可以实现动态的服务发现和管理。