問題描述

我按照zk權威指南上的代碼創建節點：

package com.zkstudy;import java.io.IOException;import java.util.Random;import org.apache.zookeeper.CreateMode;import org.apache.zookeeper.KeeperException;import org.apache.zookeeper.WatchedEvent;import org.apache.zookeeper.Watcher;import org.apache.zookeeper.ZooDefs.Ids;import org.apache.zookeeper.ZooKeeper;import org.apache.zookeeper.data.Stat;public class Master implements Watcher { private ZooKeeper zk = null; private String host; private String serverId = null; private boolean isLeader = false; public Master(String host) {this.host = host;Random radom = new Random();serverId = Integer.toHexString(radom.nextInt()); } public void start() {try { this.zk = new ZooKeeper(host, 15000, this);} catch (IOException e) { e.printStackTrace();} } public void createMaster() {while (true) { try {zk.create('/master', serverId.getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);isLeader = true;break; } catch (KeeperException e) {e.printStackTrace();isLeader = false;break; } catch (InterruptedException e) {e.printStackTrace(); } if (checkMaster()) {break; }} } public boolean checkMaster() {while (true) { Stat stat = new Stat(); try {byte[] data = zk.getData('/master', false, stat);isLeader = new String(data).equals(serverId);return true; } catch (KeeperException e) {e.printStackTrace();return false; } catch (InterruptedException e) {e.printStackTrace(); }} } public void process(WatchedEvent event) {System.out.println('watcher thread:---------->' + Thread.currentThread().getId());System.out.println('event:---------->' + event); } public static void main(String[] args) throws InterruptedException {Master master = new Master('123.206.28.37:2181');master.start();master.createMaster();if (master.isLeader) { System.out.println('i am master');}System.out.println('main thread:---------->' + Thread.currentThread().getId());Thread.sleep(5000); }}

然后我運行了兩遍。出現了如下問題：

watcher thread:---------->10event:---------->WatchedEvent state:SyncConnected type:None path:nullorg.apache.zookeeper.KeeperException$NodeExistsException: KeeperErrorCode = NodeExists for /mastermain thread:---------->1 at org.apache.zookeeper.KeeperException.create(KeeperException.java:119) at org.apache.zookeeper.KeeperException.create(KeeperException.java:51) at org.apache.zookeeper.ZooKeeper.create(ZooKeeper.java:783) at com.zkstudy.Master.createMaster(Master.java:40) at com.zkstudy.Master.main(Master.java:83)

提示master節點已經存在。但是我在命令行里面查看卻沒有發現master節點：

[zk: localhost:2181(CONNECTED) 10] ls[zk: localhost:2181(CONNECTED) 11] ls /[zk, zookeeper][zk: localhost:2181(CONNECTED) 12]

請問這是為什么呢？zk使用的是單節點，不是偽集群。

問題解答

自問自答吧。因為我創建的是臨時節點，臨時節點在繪畫斷開以后會自動刪除，估計這個 ls / 命令應該是列舉的持久節點。