Zk學習筆記——創建節點

參考：從Paxos到Zookeeper分布式一致性原理和實踐

使用的zk依賴是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在創建節點的有同步創建和異步創建，但是Zk是不支持遞歸創建節點，即父節點必須存儲。

在創建同名的節點的時候，會拋出NodeExistsException異常。

Zookeeper節點內容只支持字節數組（byte[]）

同步創建節點代碼，其中創建了一個永久節點，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();
        }
    }
}

輸出，使用Zkui查看zk中的數據，能發現多出了/app1的節點，節點的值是123

 

Zk中節點的類型分為持久節點（PERSISTENT），持久順序節點（PERSISTENT_SEQUENTIAL），臨時節點（EPHEMERAL），臨時順序節點（EPHEMERAL_SEQUENTIAL）

區別如下

異步創建節點代碼，

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);
    }
}

如果創建成功，返回的狀態碼是0

 

如果節點已經存在，返回的狀態碼是-110

具體介紹