Zookeeper之创建组，加入组，列出组成员和删除组

创建组znode

public class CreateGroup implements Watcher {  private static final int SESSION_TIMEOUT = 5000;  //ZooKeeper类是客户端API的主要类，用于维护客户端和ZooKeeper服务之间的连接  private ZooKeeper zk;  //锁存器(latch)此计数器为1，表示在释放所有等待线程之前需要发生的事件数，  private CountDownLatch connectedSignal = new CountDownLatch(1);  public void connect(String hosts) throws IOException, InterruptedException {    //参数this表示一个Watcher对象接收来自于Zookeeper的回调，以获得各种事件的通知，在此表示CreateGroup对象    zk = new ZooKeeper(hosts, SESSION_TIMEOUT, this);    connectedSignal.await();  }  @Override  public void process(WatchedEvent event) { // Watcher interface    if (event.getState() == KeeperState.SyncConnected) {      //在调用这个方法表示计数器递减1，若计数器的值变为0，则await()方法返回      connectedSignal.countDown();    }  }  public void create(String groupName) throws KeeperException,      InterruptedException {    String path = "/" + groupName;    String createdPath = zk.create(path, null/*data*/, Ids.OPEN_ACL_UNSAFE,        CreateMode.PERSISTENT);// 持久化的 znode    System.out.println("Created " + createdPath);  }  public void close() throws InterruptedException {    zk.close();  }  public static void main(String[] args) throws Exception {    CreateGroup createGroup = new CreateGroup();    createGroup.connect("192.168.8.88");    createGroup.create("zoo");    createGroup.close();  }}

加入组成员-子znode

// vv ConnectionWatcherpublic class ConnectionWatcher implements Watcher {  private static final int SESSION_TIMEOUT = 5000;  protected ZooKeeper zk;  private CountDownLatch connectedSignal = new CountDownLatch(1);  public void connect(String hosts) throws IOException, InterruptedException {    zk = new ZooKeeper(hosts, SESSION_TIMEOUT, this);    connectedSignal.await();  }  @Override  public void process(WatchedEvent event) {    if (event.getState() == KeeperState.SyncConnected) {      connectedSignal.countDown();    }  }  public void close() throws InterruptedException {    zk.close();  }}// ^^ ConnectionWatcher// vv JoinGrouppublic class JoinGroup extends ConnectionWatcher {  public void join(String groupName, String memberName) throws KeeperException,      InterruptedException {    String path = "/" + groupName + "/" + memberName;    String createdPath = zk.create(path, null/*data*/, Ids.OPEN_ACL_UNSAFE,      CreateMode.EPHEMERAL);    System.out.println("Created " + createdPath);  }  public static void main(String[] args) throws Exception {    JoinGroup joinGroup = new JoinGroup();    joinGroup.connect("192.168.8.88");    joinGroup.join("zoo", "goat");    // stay alive until process is killed or thread is interrupted    Thread.sleep(Long.MAX_VALUE);  }}// ^^ JoinGroup

列出组成员

// vv ListGrouppublic class ListGroup extends ConnectionWatcher {  public void list(String groupName) throws KeeperException,      InterruptedException {    String path = "/" + groupName;    try {      //第二个参数若为true表示对这个父节点设置监视，应用程序可以接收组成员的加入，退出和这个父组znode被删除的有关通知      List<String> children = zk.getChildren(path, false);      if (children.isEmpty()) {        System.out.printf("No members in group %s\n", groupName);        System.exit(1);      }      for (String child : children) {        System.out.println(child);      }    } catch (KeeperException.NoNodeException e) {      System.out.printf("Group %s does not exist\n", groupName);      System.exit(1);    }  }  public static void main(String[] args) throws Exception {    ListGroup listGroup = new ListGroup();    listGroup.connect("192.168.8.88");    listGroup.list("zoo");    listGroup.close();  }}// ^^ ListGroup

删除组

// vv DeleteGrouppublic class DeleteGroup extends ConnectionWatcher {  public void delete(String groupName) throws KeeperException,      InterruptedException {    String path = "/" + groupName;    try {      List<String> children = zk.getChildren(path, false);      for (String child : children) {        zk.delete(path + "/" + child, -1);//-1表示绕过版本检测机制，不管znode版本是什么直接将其删除      }      zk.delete(path, -1);    } catch (KeeperException.NoNodeException e) {      System.out.printf("Group %s does not exist\n", groupName);      System.exit(1);    }  }  public static void main(String[] args) throws Exception {    DeleteGroup deleteGroup = new DeleteGroup();    deleteGroup.connect("192.168.8.88");    deleteGroup.delete("zoo");    deleteGroup.close();  }}// ^^ DeleteGroup