Zookeeper的java客户端API使用方法（五）-蒲公英云

Zookeeper的java客户端API使用方法（五）

Bertha 。 2022-07-12 09:27 257阅读 0赞

前面几篇博文，我们简单的介绍了一下zookeeper，如何安装zookeeper集群，以及如何使用命令行等。这篇博文我们重点来看下Zookeeper的java客户端API使用方式。

创建会话

客户端可以通过创建一个Zookeeper（org.apache.zookeeper.ZooKeeper）实例来连接ZooKeeper服务器。给大家推荐一篇博文，构造方法和参数都介绍的非常的详细，看一下就好。

我们看一下建立会话的代码就好了。

public class CreateSession implements Watcher{ 
    private static ZooKeeper zookeeper;
    //创建一个与服务器的连接 需要(服务端的 ip+端口号)(session过期时间)(Watcher监听注册) 
    public static void main(String[] args) throws IOException, InterruptedException {
        zookeeper = new ZooKeeper("127.0.0.1:2181", 5000, new CreateSession());
        System.out.println(zookeeper.getState());
        Thread.sleep(Integer.MAX_VALUE);
    }
    private void doSomething(){
        System.out.println("do something");
    }
    @Override
    public void process(WatchedEvent event) {
        System.out.println("Receive watched event:" + event);
        if(event.getState() == KeeperState.SyncConnected){
            System.out.println("ZooKeeper session established.");  
            doSomething();
        }
    }
}

需要我们注意就一点：ZooKeeper 允许客户端向服务端注册一个 Watcher 监听，当服务端的一些指定事件触发了这个 Watcher，那么就会向指定客户端发送一个事件通知来实现分布式的通知功能。

zookeeper的所有的API，都有同步和异步两种方式，使用异步API时，client可为每个operation设置callback，在operation被执行后，zookeeper会执行对应的callback。

下面给大家展示一下两个方式创建节点的不同。

同步创建节点

public class CreateNodeSync implements Watcher{ 
    private static ZooKeeper zookeeper;
     //创建一个与服务器的连接 需要(服务端的 ip+端口号)(session过期时间)(Watcher监听注册) 
    public static void main(String[] args) throws IOException, InterruptedException {
        zookeeper = new ZooKeeper("127.0.0.1:2181", 5000, new CreateNodeSync());
        System.out.println(zookeeper.getState());
        Thread.sleep(Integer.MAX_VALUE);
    }
    /** * 创建Znode * CreateMode: * PERSISTENT (持续的，相对于EPHEMERAL，不会随着client的断开而消失) * PERSISTENT_SEQUENTIAL（持久的且带顺序的） * EPHEMERAL (短暂的，生命周期依赖于client session) * EPHEMERAL_SEQUENTIAL (短暂的，带顺序的) */
    private void doSomething(){
        try {
            String path = zookeeper.create("/node_2", "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            System.out.println("return path:" + path);
        } catch (KeeperException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("do something");
    }
    @Override
    public void process(WatchedEvent event) {
        System.out.println("Receive watched event:" + event);
        if(event.getState() == KeeperState.SyncConnected){
            doSomething();
        }
    }
}

异步创建节点

public class CreateNodeASync implements Watcher { 
    private static ZooKeeper zookeeper;
     //创建一个与服务器的连接 需要(服务端的 ip+端口号)(session过期时间)(Watcher监听注册) 
    public static void main(String[] args) throws IOException, InterruptedException {
        zookeeper = new ZooKeeper("127.0.0.1:2181", 5000, new CreateNodeASync());
        System.out.println(zookeeper.getState());
        Thread.sleep(Integer.MAX_VALUE);
    }
    private void doSomething() {
        zookeeper.create("/node_1", "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT,
                new IStringCallback(), "this is content");
        System.out.println("do something");
    }
    @Override
    public void process(WatchedEvent event) {
        System.out.println("Receive watched event:" + event);
        if (event.getState() == KeeperState.SyncConnected) {
            doSomething();
        }
    }
    static class IStringCallback implements AsyncCallback.StringCallback {
        @Override
        public void processResult(int rc, String path, Object ctx, String name) {
            System.out.println("rc:" + rc);
            System.out.println("path:" + path);
            System.out.println("ctx:" + ctx);
            System.out.println("name:" + name);
        }
    }
}