Zookeeper实例原生API--同步更新节点数据

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import java.util.concurrent.CountDownLatch;import org.apache.zookeeper.CreateMode;import org.apache.zookeeper.KeeperException;import org.apache.zookeeper.WatchedEvent;import org.apache.zookeeper.Watcher;import org.apache.zookeeper.Watcher.Event.EventType;import org.apache.zookeeper.Watcher.Event.KeeperState;import org.apache.zookeeper.ZooDefs.Ids;import org.apache.zookeeper.ZooKeeper;import org.apache.zookeeper.data.Stat;/** * * @ClassName: SetData_API_Sync_Usage * @Description: TODO(ZooKeeper API 更新节点数据内容，使用同步(sync)接口) * @author RongShu* @date 2017年6月11日 下午8:39:56 * */public class SetData_API_Sync_Usage implements Watcher {    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);    private static ZooKeeper zk;    public static void main(String[] args) throws Exception {    String path = "/zk-book";    zk = new ZooKeeper("localhost:2181", 5000, new SetData_API_Sync_Usage());    connectedSemaphore.await();        zk.create( path, "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL );        zk.getData( path, true, null );        Stat stat = zk.setData( path, "456".getBytes(), -1 );        System.out.println(stat.getCzxid()+","+stat.getMzxid()+","+stat.getVersion());        Stat stat2 = zk.setData( path, "456".getBytes(), stat.getVersion() );        System.out.println(stat2.getCzxid()+","+stat2.getMzxid()+","+stat2.getVersion());        try {zk.setData( path, "456".getBytes(), stat.getVersion() );} catch ( KeeperException e ) {System.out.println("Error: " + e.code() + "," + e.getMessage());}        Thread.sleep( Integer.MAX_VALUE );    }    @Override    public void process(WatchedEvent event) {        if (KeeperState.SyncConnected == event.getState()) {            if (EventType.None == event.getType() && null == event.getPath()) {                connectedSemaphore.countDown();            }        }    }}输出394,395,1394,396,2Error: BADVERSION,KeeperErrorCode = BadVersion for /zk-book

注意：

Zookeeper的setData接口中version参数是由CAS原理衍生而来，Zookeeper每个节点都有数据版本概念，在调用更新操作的时候，就可以添加version这个参数，该参数可以对应于CAS原理中的 “预期值” 表明是针对这个版本进行的更新。

Zookeeper中数据版本都是从0开始计数的，如果客户端传入的参数为-1，就是告诉Zookeeper服务端，客户端需要基于数据的最新版本进行操作。

扩展

参考

1.《从Paxos到Zookeeper：分布式一致性原理与实践》

2. https://zookeeper.apache.org/doc/r3.5.3-beta/api/index.html

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