需求

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。

需求分析

具体实现

先在集群上创建/servers节点

create /servers "servers"

一些依赖

pom.xml：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.mcq</groupId>
  <artifactId>zookeeper1026</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>RELEASE</version>
		</dependency>
		<dependency>
			<groupId>org.apache.logging.log4j</groupId>
			<artifactId>log4j-core</artifactId>
			<version>2.8.2</version>
		</dependency>
		<!-- https://mvnrepository.com/artifact/org.apache.zookeeper/zookeeper -->
		<dependency>
			<groupId>org.apache.zookeeper</groupId>
			<artifactId>zookeeper</artifactId>
			<version>3.4.10</version>
		</dependency>
</dependencies>
</project>

在src/main/resources下添加一个file log4j.properties：

log4j.rootLogger=INFO, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - %m%n
log4j.appender.logfile=org.apache.log4j.FileAppender
log4j.appender.logfile.File=target/spring.log
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=%d %p [%c] - %m%n

服务器端向 Zookeeper 注册代码

package com.mcq.zookeeper1026;

import java.io.IOException;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;

public class DistributeServer {
	private String connectString = "hadoop103:2181,hadoop104:2181,hadoop105:2181";
	private int sessionTimeOut = 2000;
	private ZooKeeper zk = null;
	private String parentNode = "/servers";

	public void getConnect() throws IOException {
		zk = new ZooKeeper(connectString, sessionTimeOut, new Watcher() {

			@Override
			public void process(WatchedEvent event) {
				// TODO Auto-generated method stub

			}

		});
	}

	// 注册服务器
	public void registServer(String hostname) throws Exception {
		System.out.println(zk);
		String path = zk.create(parentNode + "/server", hostname.getBytes(), Ids.OPEN_ACL_UNSAFE,
				CreateMode.EPHEMERAL_SEQUENTIAL);
		System.out.println(hostname + " is online " + path);
	}

	// 业务功能
	public void business(String hostname) throws InterruptedException {
		System.out.println(hostname + " is working ……");
		Thread.sleep(Long.MAX_VALUE);
	}

	public static void main(String[] args) throws Exception {
		// 1.获取zk连接
		DistributeServer server = new DistributeServer();
		server.getConnect();
		// 2.利用zk连接注册服务器信息
		server.registServer(args[0]);
		// 3.启动业务功能
		server.business(args[0]);

	}
}

客户端代码

package com.mcq.zookeeper1026;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

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

public class DistributeClient {
	public static void main(String[] args) throws IOException, KeeperException, InterruptedException {
		//1.获取zk连接
		DistributeClient client=new DistributeClient();
		client.getConnect();
		//2.获取servers的子节点信息，从中获取服务器信息列表
		client.getServerList();
		//3.业务进程启动
		client.business();
	}

	private void business() throws InterruptedException {
		// TODO Auto-generated method stub
		System.out.println("client is working ……");
		Thread.sleep(Long.MAX_VALUE);
	}

	private String parentNode="/servers";

	private void getServerList() throws KeeperException, InterruptedException {
		// TODO Auto-generated method stub
		//1.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);
		//2.存储服务器信息列表
		ArrayList<String> servers=new ArrayList<>();
		//3.遍历所有节点，获取节点中的主机名称信息
		for(String child:children) {
			byte[] data=zk.getData(parentNode+"/"+child,false,null);
			servers.add(new String(data));
		}
		//4.打印服务器列表信息
		System.out.println(servers);
	}

	private ZooKeeper zk=null;
	private String connectString="hadoop103:2181,hadoop104:2181,hadoop105:2181";
	private int sessionTimeOut=2000;

	private void getConnect() throws IOException {
		// TODO Auto-generated method stub
		//创建到zk的客户端连接
		zk=new ZooKeeper(connectString,sessionTimeOut,new Watcher() {

			@Override
			public void process(WatchedEvent event) {
				// TODO Auto-generated method stub
				try {
					getServerList();
				}catch(Exception e) {
					e.printStackTrace();
				}
			}

		});
	}
}

运行程序

先运行客户端

在xshell上登录客户端（bin/zkCli.sh）,进行一些操作，可以看到eclipse的控制台会实时输出有哪些节点。

然后运行服务器端，记得先在run configuration里设置一下参数，比如设成hadoop103，那么运行后，客户端的控制台会实时显示当前的节点。

点上面那个红框可以切换控制台。

原文地址：https://www.cnblogs.com/mcq1999/p/11743939.html