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上一章我们知道zookeeper的简介，启动，设置节点以及结构性能。本小节我们来玩玩api，获取下数据。
读一下：http://zookeeper.apache.org/doc/trunk/javaExample.html
然后我说 what the fuck it is？
我就想读个数据，需要这么复杂么。。。
动手改一下
版本1: 只获取数据，不管别的：
import org.apache.zookeeper.KeeperException; import org.apache.zookeeper.ZooKeeper; import java.io.IOException; public class ZkReader { public static void main(String[] args) throws IOException, InterruptedException, KeeperException { String hostPort = "192.168.1.2,192.168.1.3,192.168.1.4"; String znode = "/test"; ZooKeeper zk = new ZooKeeper(hostPort, 3000, null); System.out.println(new String(zk.getData(znode,false,null))); } }
在zkcli上创建 /test 并改变它的值：123，运行，输出：
123
能得到结果，但是报错了：
14/10/17 11:51:58 ERROR zookeeper.ClientCnxn: Error while calling watcher java.lang.NullPointerException at org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:521) at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:497)
看下源码，需要注册个watcher，意思是不这样zookeeper就只是个纯配置了？ok
版本2：zk get data＋watcher
import org.apache.zookeeper.KeeperException; import org.apache.zookeeper.WatchedEvent; import org.apache.zookeeper.Watcher; import org.apache.zookeeper.ZooKeeper; import java.io.IOException; public class ZkReader { public static void main(String[] args) throws IOException, InterruptedException, KeeperException { String hostPort = "10.16.73.22,10.16.73.12,10.16.73.13"; String znode = "/test"; ZooKeeper zk = new ZooKeeper(hostPort, 3000, new MyWatcher()); System.out.println(new String(zk.getData(znode,false,null))); } } class MyWatcher implements Watcher { @Override public void process(WatchedEvent event) { System.out.println("hello zookeeper"); System.out.println(String.format("hello event! type=%s, stat=%s, path=%s",event.getType(),event.getState(),event.getPath())); } }
输出却是：
hello zookeeper
123
hello event! type=None, stat=SyncConnected, path=null
data总是在中间？百撕不得姐，在邮件组里咨询下，等答案
这两个版本只是做到了获取数据，如果数据有变动，需要自动更新呢？ok，看第三个版本：
标签：style blog http color io os ar java for
原文地址：http://www.cnblogs.com/shenguanpu/p/4030855.html
