[网络协议]Zookeeper案例

1.服务器动态上下线（任意一台客户端都能实时感知到主节点服务器的上下线）
思路：
服务器启动时在Zookeeper上/service下创建临时子节点，下线时会自动删除znode
客户端获取/service下所有子节点(即所有服务)并注册监听，当子节点有变化时会通知客户端并调用process()，同时在process()中再次启动监听

(1)在集群上创建/servers 节点
[zk: localhost:2181(CONNECTED) 10] create /servers "servers"

(2)服务注册
public class ServiceRegistry {

    private static ZooKeeper zk = null;

    public static void main(String[] args) throws Exception {
        //获取zk连接
        getConnect();
        //注册服务(创建临时子节点)
        createNode();
        //服务一直运行
        Thread.sleep(Integer.MAX_VALUE);
    }

    public static void getConnect() {
        try {
            zk = new ZooKeeper("192.168.196.129:2181", 30000, new Watcher() {
                @Override
                public void process(WatchedEvent watchedEvent) {

                }
            });
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //在/servers下创建带序列号的临时子节点
    public static void createNode() {
        try {
            String nodeCreated = zk.create("/servers/server", "节点数据".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    
}

(3)客户端
public class zkClient {

    private static ZooKeeper zk = null;

    public static void main(String[] args) throws Exception {
        //获取zk连接
        getConnect();
        //获取服务(获取子节点)
        getChildren();
        //服务一直运行
        Thread.sleep(Integer.MAX_VALUE);
    }

    public static void getConnect() {
        try {
            zk = new ZooKeeper("192.168.196.129:2181", 30000, new Watcher() {
                @Override
                public void process(WatchedEvent watchedEvent) {
                    //收到事件通知后的回调函数
                    System.out.println("监听回调：" + watchedEvent);
                    try {
                        //再次启动监听
                        List<String> children = zk.getChildren("/servers", true);
                        children.forEach(e -> System.out.println(e));
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 获取子节点
    public static void getChildren() {
        try {
            List<String> children = zk.getChildren("/servers", true);
            children.forEach(e -> System.out.println(e));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

2.分布式锁