Zk学习笔记——创建节点

参考：从Paxos到Zookeeper分布式一致性原理和实践

使用的zk依赖是cdh5.16.2的3.4.5

<!-- zookeeper -->
<dependency>
    <groupId>org.apache.zookeeper</groupId>
    <artifactId>zookeeper</artifactId>
    <version>3.4.5-cdh5.16.2</version>
</dependency>

Zk在创建节点的有同步创建和异步创建，但是Zk是不支持递归创建节点，即父节点必须存储。

在创建同名的节点的时候，会抛出NodeExistsException异常。

Zookeeper节点内容只支持字节数组（byte[]）

同步创建节点代码，其中创建了一个永久节点，key是/app1，value是123

package com.bigdata.zookeeper;


import org.apache.zookeeper.*;
import java.util.concurrent.CountDownLatch;

public class ZkExample implements Watcher {

    public static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    public static void main(String[] args) throws Exception {
        ZooKeeper zk = new ZooKeeper("master:2181", 5000, new ZkExample());
        System.out.println(zk.getState());
        try {
            connectedSemaphore.await();
            String path = zk.create("/app1", "123".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            System.out.println("success create znode: " + path);
        } catch (InterruptedException e) {
            System.out.println("Zk session established" + e);
        }
    }

    @Override
    public void process(WatchedEvent watchedEvent) {
        System.out.println(watchedEvent);
        if (Event.KeeperState.SyncConnected == watchedEvent.getState()) {
            connectedSemaphore.countDown();
        }
    }
}

输出，使用Zkui查看zk中的数据，能发现多出了/app1的节点，节点的值是123

Zk中节点的类型分为持久节点（PERSISTENT），持久顺序节点（PERSISTENT_SEQUENTIAL），临时节点（EPHEMERAL），临时顺序节点（EPHEMERAL_SEQUENTIAL）

区别如下

异步创建节点代码，

package com.bigdata.zookeeper;


import org.apache.zookeeper.*;

import java.util.concurrent.CountDownLatch;

public class ZkExample implements Watcher {

    public static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    public static void main(String[] args) throws Exception {
        ZooKeeper zk = new ZooKeeper("master:2181", 5000, new ZkExample());
        System.out.println(zk.getState());
        try {
            connectedSemaphore.await();
            zk.create("/app2", "123".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,
                    CreateMode.PERSISTENT, new IStringCallback(), "This is context");
            Thread.sleep(Integer.MAX_VALUE);
        } catch (InterruptedException e) {
            System.out.println("Zk session established" + e);
        }
    }

    @Override
    public void process(WatchedEvent watchedEvent) {
        System.out.println(watchedEvent);
        if (Event.KeeperState.SyncConnected == watchedEvent.getState()) {
            connectedSemaphore.countDown();
        }
    }
}

class IStringCallback implements AsyncCallback.StringCallback {

    @Override
    public void processResult(int i, String s, Object o, String s1) {
        System.out.println("Create path result : [" + i + ", " + s + ", " + o + ", real path name : " + s1);
    }
}

如果创建成功，返回的状态码是0

如果节点已经存在，返回的状态码是-110

具体介绍