Zookeeper客户端API之读取子节点内容（九）
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)public void getData(final String path, Watcher watcher,
DataCallback cb, Object ctx)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。
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原始发表：2017-03-27 ，如有侵权请联系 cloudcommunity@tencent.com 删除
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