加入组

接下来我们实现如何在一个组中注册成员。我们将使用ephemeral znode来创建这些成员节点。那么当客户端程序退出时，这些成员将被删除。

我们创建一个ConnetionWatcher类，然后继承实现一个JoinGroup类：

  1. public class ConnectionWatcher implements Watcher {
  3.  private static final int SESSION_TIMEOUT = 5000;
  5.  protected ZooKeeper zk;
  7.  private CountDownLatch connectedSignal = new CountDownLatch(1);
  9.  public void connect(String hosts) throws IOException, InterruptedException {
  10.      zk = new ZooKeeper(hosts, SESSION_TIMEOUT, this);
  11.      connectedSignal.await();
  12.  }
  14.  @Override
  15.  public void process(WatchedEvent event) {
  16.      if (event.getState() == KeeperState.SyncConnected) {
  17.          connectedSignal.countDown();
  18.      }
  19.  }
  21.  public void close() throws InterruptedException {
  22.      zk.close();
  23.  }
  24. }
  1. public class JoinGroup extends ConnectionWatcher {
  3.  public void join(String groupName, String memberName) throws KeeperException,
  4.  InterruptedException {
  5.      String path = "/" + groupName + "/" + memberName;
  6.      String createdPath = zk.create(path, null/*data*/, Ids.OPEN_ACL_UNSAFE,
  7.      CreateMode.EPHEMERAL);
  8.      System.out.println("Created " + createdPath);
  9.  }
  11.  public static void main(String[] args) throws Exception {
  12.      JoinGroup joinGroup = new JoinGroup();
  13.      joinGroup.connect(args[0]);
  14.      joinGroup.join(args[1], args[2]);
  15.      // stay alive until process is killed or thread is interrupted
  16.      Thread.sleep(Long.MAX_VALUE);
  17.  }
  18. }

加入组与创建组非常相似。我们加入了一个ephemeral znode后，让线程阻塞住。然后我们可以使用命令行查看zookeeper中我们创建的znode。当我们将阻塞的程序强行关闭后，我们会发现我们创建的znode会自动消失。