学习笔记：Zookeeper 应用案例(上下线动态感知)

1、Zookeeper 应用案例(上下线动态感知)

8.1 案例1——服务器上下线动态感知

8.1.1 需求描述

某分布式系统中，主节点可以有多台，可以动态上下线

任意一台客户端都能实时感知到主节点服务器的上下线

8.1.2 设计思路

8.1.3 代码开发

1、客户端实现

package cn.com.toto.zkonlineoroffline;

import java.util.ArrayList;

import java.util.List;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.ZooKeeper;

public class DistributedClient {

private static final String connectString = "192.168.106.80:2181,192.168.106.81:2181,192.168.106.82:2181";

private static final int sessionTimeout = 2000;

private static final String parentNode = "/servers";

// 注意:加volatile的意义何在？

private volatile List<String> serverList;

private ZooKeeper zk = null;

/**

* 创建到zk的客户端连接

*

* @throws Exception

*/

public void getConnect() throws Exception {

zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {

@Override

public void process(WatchedEvent event) {

// 收到事件通知后的回调函数（应该是我们自己的事件处理逻辑）

try {

//重新更新服务器列表，并且注册了监听

getServerList();

} catch (Exception e) {

}

}

});

}

/**

* 获取服务器信息列表

*

* @throws Exception

*/

public void getServerList() throws Exception {

// 获取服务器子节点信息，并且对父节点进行监听

List<String> children = zk.getChildren(parentNode, true);

// 先创建一个局部的list来存服务器信息

List<String> servers = new ArrayList<String>();

for (String child : children) {

// child只是子节点的节点名

byte[] data = zk.getData(parentNode + "/" + child, false, null);

servers.add(new String(data));

}

// 把servers赋值给成员变量serverList，已提供给各业务线程使用

serverList = servers;

//打印服务器列表

System.out.println(serverList);

}

/**

* 业务功能

*

* @throws InterruptedException

*/

public void handleBussiness() throws InterruptedException {

System.out.println("client start working.....");

Thread.sleep(Long.MAX_VALUE);

}

public static void main(String[] args) throws Exception {

// 获取zk连接

DistributedClient client = new DistributedClient();

client.getConnect();

// 获取servers的子节点信息（并监听），从中获取服务器信息列表

client.getServerList();

// 业务线程启动

client.handleBussiness();

}

}

2、服务器端实现

package cn.com.toto.zkonlineoroffline;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.ZooKeeper;

import org.apache.zookeeper.Watcher.Event.KeeperState;

import org.apache.zookeeper.ZooDefs.Ids;

import org.apache.zookeeper.data.Stat;

public class DistributedServer {

private static final String CONNECT_STRING = "192.168.106.80:2181,192.168.106.81:2181,192.168.106.82:2181";

private static final int SESSION_TIME_OUT = 2000;

private static final String PARENT_NODE = "/servers";

private ZooKeeper zk = null;

CountDownLatch countDownLatch = new CountDownLatch(1);

/**

* 创建到zk的客户端连接

*

* @throws Exception

*/

public void getConnect() throws Exception {

zk = new ZooKeeper(CONNECT_STRING, SESSION_TIME_OUT, new Watcher() {

@Override

public void process(WatchedEvent event) {

if(event.getState()==KeeperState.SyncConnected){

countDownLatch.countDown();

}

}

});

countDownLatch.await();

}

/**

* 向zk集群注册服务器信息

*

* @param hostname

* @throws Exception

*/

public void registerServer(String hostname) throws Exception {

Stat exists = zk.exists(PARENT_NODE, false);

if(exists==null) zk.create(PARENT_NODE, null, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

String path = zk.create(PARENT_NODE + "/server", hostname.getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);

System.out.println(hostname + "is online.." + path);

}

/**

* 业务功能

*

* @throws InterruptedException

*/

public void handleBussiness(String hostname) throws InterruptedException {

System.out.println(hostname + "start working.....");

Thread.sleep(Long.MAX_VALUE);

}

public static void main(String[] args) throws Exception {

DistributedServer server = new DistributedServer();

// 获取zk连接

server.getConnect();

// 利用zk连接注册服务器信息(主机名)

server.registerServer(args[0]);

// 启动业务功能

server.handleBussiness(args[0]);

}

}