zookeeper客户端使用

客户端API常规应用

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zookeeper 提供了java与C两种语言的客户端。我们要学习的就是java客户端。引入最新的maven依赖：

<dependency>
  <groupId>org.apache.zookeeper</groupId>
  <artifactId>zookeeper</artifactId>
  <version>3.6.2</version>
</dependency>

初始连接

常规的客户端类是 org.apache.zookeeper.ZooKeeper，实例化该类之后将会自动与集群建立连接。

• connectString 连接串，包括ip+端口 ,集群模式下用逗号隔开
• sessionTimeout 会话超时时间，该值不能超过服务端所设置的 minSessionTimeout 和maxSessionTimeout
• watcher 会话监听器，服务端事件将会触该监听

zooKeeper = new ZooKeeper("192.168.2.103:2181", 4000, new Watcher() {
  @Override
  public void process(WatchedEvent watchedEvent) {
    System.out.println("init:"+watchedEvent.getPath());
  }
});

创建、查看节点

创建节点

通过org.apache.zookeeper.ZooKeeper#create()即可创建节点

public void createData() throws InterruptedException, KeeperException {
  List<ACL> aclList = new ArrayList<>();
  int perm = ZooDefs.Perms.ADMIN | ZooDefs.Perms.READ;
  
  // perms 对应权限位permission
  // id 对应权限模式scheme + id
  ACL acl1 = new ACL(perm, new Id("world","anyone"));
  ACL acl2 = new ACL(perm, new Id("ip","192.168.2.103"));
  ACL acl3 = new ACL(perm, new Id("ip","127.0.0.1"));

  aclList.add(acl1);
  aclList.add(acl2);
  aclList.add(acl3);
  zooKeeper.create("/hello", "hello word!".getBytes(), aclList, CreateMode.PERSISTENT);
}

运行完成后，在zookeeper进行查看

[zk: 127.0.0.1:2181(CONNECTED) 64] getAcl /hello
'world,'anyone
: ra
'ip,'192.168.2.103
: ra
'ip,'127.0.0.1
: ra
[zk: 127.0.0.1:2181(CONNECTED) 65] get /hello
hello word

查看节点

查看当前节点

通过org.apache.zookeeper.ZooKeeper#getData()即可查看节点

public void testData() throws InterruptedException, KeeperException {
  final byte[] keeperData = zooKeeper.getData("/pyr", false, null);
  System.out.println("testData:" + new String(keeperData));
}

查看子节点

通过org.apache.zookeeper.ZooKeeper#getChildren()即可获取子节点

public void testGetChildrenWithoutWatch() throws InterruptedException, KeeperException {
  final List<String> children = zooKeeper.getChildren("/pyr", false);
  children.stream().forEach(System.out::println);
}

监听节点

• 在getData() 与getChildren()两个方法中可分别设置监听数据变化和子节点变化。

• 通过设置watch为true，当前事件触发时会调用zookeeper()构建函数中Watcher.process()方法。也可以添加watcher参数来实现自定义监听。一般采用后者。

• 所有的监听都是一次性的，如果要持续监听需要触发后在添加一次监听。

使用默认监听

public void testGetDataWithWatcher() throws InterruptedException, KeeperException {
  final byte[] keeperData = zooKeeper.getData("/pyr", true, null);
  System.out.println("testGetDataWithWatcher:" + new String(keeperData));
  Thread.sleep(Long.MAX_VALUE);
}

自定义监听

public void testGetDataWithCustomWatcher() throws InterruptedException, KeeperException {
  final byte[] keeperData = zooKeeper.getData("/pyr", new Watcher() {
    @Override
    public void process(WatchedEvent watchedEvent) {
      try {
        zooKeeper.getData("/temp", this, null);
      } catch (KeeperException | InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("testGetDataWithCustomWatcher:" + watchedEvent.getPath());

    }
  }, null);
  Thread.sleep(Long.MAX_VALUE);
}

第三方客户端ZkClient

zkClient 是在zookeeper客户端基础之上封装的，使用上更加友好。主要变化如下：

• 可以设置持久监听，或删除某个监听
• 可以插入JAVA对象，自动进行序列化和反序列化
• 简化了基本的增删改查操作。