Zookeeper客户端API之读取子节点内容（九）

2022-01-10 13:51:58

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

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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