本篇博客介绍一下Zookeeper原声API读取节点内容的使用方法。
读取节点内容方法介绍
方法
Zookeeper提供了两个方法来获取节点内容，同步获取和异步获取：
public byte[] getData(String path, boolean watch, Stat stat)
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public void getData(final String path, Watcher watcher,
DataCallback cb, Object ctx)
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参数说明
参数 说明
path 指定数据节点的路径，获取该节点下面的子节点
watcher 注册在path上的Watcher。节点变更会通知会向客户端发起通知。
stat 指定数据节点状态信息。传入旧stat，方法执行过程中会将其替换为新stat对象。
watch 表示是否需要注册一个watcher。true：注册默认watcher，false：不需要注册watcher
cb 注册一个异步回调函数
ctx 传递上下文信息
具体案例
同步方法
package com.secbro.learn; import org.apache.zookeeper.*; import org.apache.zookeeper.data.Stat; import java.util.concurrent.CountDownLatch; /** * 读取节点数据 * Created by zhuzs on 2017/3/27. */ public class TestGetData implements Watcher{ private static CountDownLatch countDownLatch = new CountDownLatch(1); private static ZooKeeper zooKeeper; private static Stat stat = new Stat(); public static void main(String[] args) throws Exception{ zooKeeper = new ZooKeeper("127.0.0.1:2181", 5000, new TestGetData()); countDownLatch.await(); String path = "/test-get-data"; zooKeeper.create(path,"123".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); System.out.println("同步读取节点内容：" + new String(zooKeeper.getData(path,true,stat))); System.out.println("同步读取Stat：czxid=" + stat.getCzxid() + ";mzxid=" + stat.getMzxid() + ";version=" + stat.getVersion()); zooKeeper.setData(path,"123".getBytes(),-1); Thread.sleep(10000); } public void process(WatchedEvent event) { if (Event.KeeperState.SyncConnected == event.getState()) { if(Event.EventType.None == event.getType() && null == event.getPath()){ // 连接时的监听事件 countDownLatch.countDown(); } else if (event.getType() == Event.EventType.NodeDataChanged){ // 子节点内容变更时的监听 try { System.out.println("监听获得通知内容：data=" + new String(zooKeeper.getData(event.getPath(),true,stat))); System.out.println("监听获得通知Stat：czxid=" + stat.getCzxid() + ";mzxid=" + stat.getMzxid() + ";version=" + stat.getVersion()); } catch (Exception e) { e.printStackTrace(); } } } } }
运行结果：
同步读取节点内容：123
同步读取Stat：czxid=14700;mzxid=14700;version=0
监听获得通知内容：data=123
监听获得通知Stat：czxid=14700;mzxid=14701;version=1
代码的基本逻辑为创建一个临时节点，然后读取临时节点内容，并注册监听，当节点变化（内容变化或版本信息变化），触发监听事件，获取最新的节点信息。
异步方法
package com.secbro.learn; import org.apache.zookeeper.*; import org.apache.zookeeper.data.Stat; import java.util.concurrent.CountDownLatch; /** * 读取节点数据 * Created by zhuzs on 2017/3/27. */ public class TestGetData implements Watcher{ private static CountDownLatch countDownLatch = new CountDownLatch(1); private static ZooKeeper zooKeeper; private static Stat stat = new Stat(); public static void main(String[] args) throws Exception{ zooKeeper = new ZooKeeper("127.0.0.1:2181", 5000, new TestGetData()); countDownLatch.await(); String path = "/test-get-data"; zooKeeper.create(path,"123".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); // 异步读取节点内容 zooKeeper.getData(path,true,new MyDataCallback(),null); zooKeeper.setData(path,"123".getBytes(),-1); Thread.sleep(10000); } public void process(WatchedEvent event) { if (Event.KeeperState.SyncConnected == event.getState()) { if(Event.EventType.None == event.getType() && null == event.getPath()){ // 连接时的监听事件 countDownLatch.countDown(); } else if (event.getType() == Event.EventType.NodeDataChanged){ // 子节点内容变更时的监听 try { System.out.println("监听获得通知内容：data=" + new String(zooKeeper.getData(event.getPath(),true,stat))); System.out.println("监听获得通知Stat：czxid=" + stat.getCzxid() + ";mzxid=" + stat.getMzxid() + ";version=" + stat.getVersion()); } catch (Exception e) { e.printStackTrace(); } } } } } class MyDataCallback implements AsyncCallback.DataCallback{ public void processResult(int rc, String path, Object ctx, byte[] data, Stat stat) { System.out.println("异步返回结果：rc=" + rc + ";path=" + path + ";data=" + new String(data)); System.out.println("异步读取Stat：czxid=" + stat.getCzxid() + ";mzxid=" + stat.getMzxid() + ";version=" + stat.getVersion()); } }
运行结果：
异步返回结果：rc=0;path=/test-get-data;data=123
异步读取Stat：czxid=14704;mzxid=14704;version=0
监听获得通知内容：data=123
监听获得通知Stat：czxid=14704;mzxid=14705;version=1
异步方法与同步方法业务逻辑基本相同，区别点在于将同步获取改为异步获取。
