Zookeeper学习笔记十之 异步实现主节点选举

异步实现主节点选举 

    Zookeeper中，所有同步调用方法都有对应的异步调用方法，通过异步调用，我们可以在单线程中同时进行多个调用，接下来实现一个异步实现主节点选举的例子

       Zookeeper.create方法的异步调用版本

       void create(String path, byte data[], List acl, CreateMode createMode, AsyncCallback.StringCallback cb,Object ctx) ，相较于同步调用，多了StringCallback ，和Object两个参数。StringCallback 提供回调方法的对象，Object用户指定上下文信息

代码示例

package com.my.service;

import java.io.IOException;
import java.util.Random;

import org.apache.zookeeper.AsyncCallback.DataCallback;
import org.apache.zookeeper.AsyncCallback.StringCallback;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException.Code;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;

public class MyZookeeper {

	private ZooKeeper zooKeeper;
	private String hostPort;
	private Random random = new Random(47);
	private String serverId = Integer.toString(random.nextInt());
	boolean isMaster = false;

	public MyZookeeper(String hostPort) {
		this.hostPort = hostPort;
	}

	// 创建一个zk连接监视点，打印断开连接日志信息
	Watcher watcher = new Watcher() {

		public void process(WatchedEvent event) {
			// 如果监控到与服务端连接断开，打印日志
			if (KeeperState.Disconnected.equals(event.getState())) {
				System.out.println("Zookeeper Disconnected!客户端与ZooKeeper服务器连接断开!");
			}

		}

	};

	// 连接到zk服务端
	public void startZk() throws IOException {
		zooKeeper = new ZooKeeper(hostPort, 15000, watcher);
	}

	public void stopZk() throws InterruptedException {
		zooKeeper.close();
	}

	// 实现一个回调的接口，并创建实例
	StringCallback masterCallback = new StringCallback() {

		public void processResult(int rc, String path, Object ctx, String name) {
			switch (Code.get(rc)) {// rc返回调用的结构，返回OK或与KeeperException异常对应的编码值
			case CONNECTIONLOSS:
				checkMasterSync();
				return;
			case OK:
				//创建成功，成为主节点
				isMaster = true;
				break;
			default:
				isMaster = false;
			}
			System.out.println("I am" + (isMaster ? "" : "not") + " the master");
		}
	};
	// 实现一个检查数据的回调接口，并创建实例
	DataCallback masterCheckCallBack = new DataCallback() {

		public void processResult(int rc, String path, Object ctx, byte[] data, Stat stat) {
			switch (Code.get(rc)) {
			case CONNECTIONLOSS:
				checkMasterSync();
				return;
			case NONODE:
				//主节点不存在,进行异步主节点创建
				runForMasterSync();
				return;

			}
		}

	};

	public void checkMasterSync() {
		zooKeeper.getData("/master", false, masterCheckCallBack, null);
	}

	public void runForMasterSync() {
		zooKeeper.create("/master", serverId.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL,
				masterCallback, null);
	}

	public static void main(String[] args) throws IOException, InterruptedException {

		MyZookeeper myZookeeper = new MyZookeeper("127.0.0.1:2181");
		myZookeeper.startZk();
		myZookeeper.runForMasterSync();
		//线程休眠一段时间，观看异步创建效果
		Thread.sleep(5000);
		if (myZookeeper.isMaster) {
			System.out.println("我是主节点");
			Thread.sleep(60000);
		} else {
			System.out.println("其他节点已经成为了主节点");
		}
	}
}