本篇部落格介紹一下Zookeeper原聲API讀取節點內容的使用方法。

讀取節點內容方法介紹

方法

Zookeeper提供了兩個方法來獲取節點內容，同步獲取和非同步獲取：

public byte[] getData(String path, boolean watch, Stat stat)

public void getData(final String path, Watcher watcher,
            DataCallback cb, Object ctx)

引數說明

具體案例

同步方法

package com.secbro.learn;

import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;

import
 
 java.util.concurrent.CountDownLatch;

/**
 *  讀取節點資料
 * 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("同步讀取節點內容：" + new String(zooKeeper.getData(path,true,stat)));
        System.out.println("同步讀取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()){ // 連線時的監聽事件
                countDownLatch.countDown();
            } else if (event.getType() == Event.EventType.NodeDataChanged){ // 子節點內容變更時的監聽
                try {
                    System.out.println("監聽獲得通知內容：data="
                            + new String(zooKeeper.getData(event.getPath(),true,stat)));
                    System.out.println("監聽獲得通知Stat：czxid=" + stat.getCzxid()
                            + ";mzxid=" + stat.getMzxid() + ";version="  + stat.getVersion());
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

執行結果：

同步讀取節點內容：123
同步讀取Stat：czxid=14700;mzxid=14700;version=0
監聽獲得通知內容：data=123
監聽獲得通知Stat：czxid=14700;mzxid=14701;version=1

程式碼的基本邏輯為建立一個臨時節點，然後讀取臨時節點內容，並註冊監聽，當節點變化（內容變化或版本資訊變化），觸發監聽事件，獲取最新的節點資訊。

非同步方法

package com.secbro.learn;

import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;

import java.util.concurrent.CountDownLatch;

/**
 *  讀取節點資料
 * 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);
        // 非同步讀取節點內容
        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()){ // 連線時的監聽事件
                countDownLatch.countDown();
            } else if (event.getType() == Event.EventType.NodeDataChanged){ // 子節點內容變更時的監聽
                try {
                    System.out.println("監聽獲得通知內容：data="
                            + new String(zooKeeper.getData(event.getPath(),true,stat)));
                    System.out.println("監聽獲得通知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("非同步返回結果：rc=" + rc + ";path=" + path + ";data=" + new String(data));
        System.out.println("非同步讀取Stat：czxid=" + stat.getCzxid()
                + ";mzxid=" + stat.getMzxid() + ";version="  + stat.getVersion());
    }
}

執行結果：

非同步返回結果：rc=0;path=/test-get-data;data=123
非同步讀取Stat：czxid=14704;mzxid=14704;version=0
監聽獲得通知內容：data=123
監聽獲得通知Stat：czxid=14704;mzxid=14705;version=1

非同步方法與同步方法業務邏輯基本相同，區別點在於將同步獲取改為非同步獲取。