zookeeper持续监听znode节点变化

2019独角兽企业重金招聘Python工程师标准>>>

总共两个类 代码就不多讲了.

main测试主方法在类Executor里。

Executor类

package com.steven.test.zk;

/**
 * A simple example program to use DataMonitor to start and
 * stop executables based on a znode. The program watches the
 * specified znode and saves the data that corresponds to the
 * znode in the filesystem. It also starts the specified program
 * with the specified arguments when the znode exists and kills
 * the program if the znode goes away.
 */
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Executor implements Watcher, Runnable, DataMonitor.DataMonitorListener {
	String znode;

	DataMonitor dm;

	ZooKeeper zk;

	Process child;

	public Executor(String hostPort, String znode) throws KeeperException, IOException {
		zk = new ZooKeeper(hostPort, 3000, this);
		dm = new DataMonitor(zk, znode, null, this);
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		args = new String[]{"localhost:2181","/teststeven"};
		String hostPort = args[0];
		String znode = args[1];
		try {
			new Executor(hostPort, znode).run();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	/***************************************************************************
	 * We do process any events ourselves, we just need to forward them on.
	 *
	 * @see org.apache.zookeeper.Watcher#process(org.apache.zookeeper.proto.WatcherEvent)
	 */
	public void process(WatchedEvent event) {
		dm.process(event);
	}

	public void run() {
		try {
			synchronized (this) {
				while (!dm.dead) {
					wait();
				}
			}
		} catch (InterruptedException e) {
		}
	}

	public void closing(int rc) {
		synchronized (this) {
			notifyAll();
		}
	}

	static class StreamWriter extends Thread {
		OutputStream os;

		InputStream is;

		StreamWriter(InputStream is, OutputStream os) {
			this.is = is;
			this.os = os;
			start();
		}

		public void run() {
			byte b[] = new byte[80];
			int rc;
			try {
				while ((rc = is.read(b)) > 0) {
					os.write(b, 0, rc);
				}
			} catch (IOException e) {
			}

		}
	}

	public void exists(byte[] data) {
		if (data == null) {
			if (child != null) {
				System.out.println("Killing process");
				child.destroy();
				try {
					child.waitFor();
				} catch (InterruptedException e) {
				}
			}
			child = null;
		} else {
			if (child != null) {
				System.out.println("Stopping child");
				child.destroy();
				try {
					child.waitFor();
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
			//other class
		}
	}
}

DataMonitor类
要监控数据主要看DataMonitor类

/**
 * A simple class that monitors the data and existence of a ZooKeeper
 * node. It uses asynchronous ZooKeeper APIs.
 */
import java.util.Arrays;

import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.AsyncCallback.StatCallback;
import org.apache.zookeeper.KeeperException.Code;
import org.apache.zookeeper.data.Stat;

public class DataMonitor implements Watcher, StatCallback {

	ZooKeeper zk;

	String znode;

	Watcher chainedWatcher;

	boolean dead;

	DataMonitorListener listener;

	byte prevData[];

	public DataMonitor(ZooKeeper zk, String znode, Watcher chainedWatcher, DataMonitorListener listener) {
		this.zk = zk;
		this.znode = znode;
		this.chainedWatcher = chainedWatcher;
		this.listener = listener;
		// Get things started by checking if the node exists. We are going
		// to be completely event driven
		zk.exists(znode, true, this, null);
	}

	/**
	 * Other classes use the DataMonitor by implementing this method
	 */
	public interface DataMonitorListener {
		/**
		 * The existence status of the node has changed.
		 */
		void exists(byte data[]);

		/**
		 * The ZooKeeper session is no longer valid.
		 *
		 * @param rc
		 *            the ZooKeeper reason code
		 */
		void closing(int rc);
	}

	public void process(WatchedEvent event) {
		String path = event.getPath();
		if (event.getType() == Event.EventType.None) {
			// We are are being told that the state of the
			// connection has changed
			switch (event.getState()) {
			case SyncConnected:
				// In this particular example we don't need to do anything
				// here - watches are automatically re-registered with
				// server and any watches triggered while the client was
				// disconnected will be delivered (in order of course)
				break;
			case Expired:
				// It's all over
				dead = true;
				listener.closing(KeeperException.Code.SessionExpired);
				break;
			}
		} else {
			if (path != null && path.equals(znode)) {
				// Something has changed on the node, let's find out
				zk.exists(znode, true, this, null);
			}
		}
		if (chainedWatcher != null) {
			chainedWatcher.process(event);
		}
	}

	public void processResult(int rc, String path, Object ctx, Stat stat) {
		boolean exists;
		switch (rc) {
		case Code.Ok:
			exists = true;
			break;
		case Code.NoNode:
			exists = false;
			break;
		case Code.SessionExpired:
		case Code.NoAuth:
			dead = true;
			listener.closing(rc);
			return;
		default:
			// Retry errors
			zk.exists(znode, true, this, null);
			return;
		}

		byte b[] = null;
		if (exists) {
			try {
				b = zk.getData(znode, false, null);
			} catch (KeeperException e) {
				// We don't need to worry about recovering now. The watch
				// callbacks will kick off any exception handling
				e.printStackTrace();
			} catch (InterruptedException e) {
				return;
			}
		}
		if ((b == null && b != prevData) || (b != null && !Arrays.equals(prevData, b))) {
			listener.exists(b);
			prevData = b;
		}
	}
}

其实官方已经给出监听文档，百度搜索代码的质量越来越low了，搜出来的东西还是一个模子刻出来。
参考官网地址：https://zookeeper.apache.org/doc/r3.1.2/javaExample.html

转载于:https://my.oschina.net/stevenliuit/blog/1589594