zookeeper的Java端API应用

1. 基本使用

org.apache.zookeeper.Zookeeper是客户端入口主类，负责建立与server的会话。它提供了表1所示几类主要方法：

功能	描述
create	在本地目录树中创建一个节点
delete	删除一个节点
exists	测试本地是否存在目标节点
get/set data	从目标节点上读取/写数据
get/set ACL	获取/设置目标节点访问控制列表信息
get children	检索一个子节点上的列表
sync	等待要被传送的数据

表1：ZooKeeper API描述

2.pom.xml配置依赖包

在本篇文章中共用一个pom.xml

<dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.10</version>
    </dependency>
    <dependency>
      <groupId>org.apache.zookeeper</groupId>
      <artifactId>zookeeper</artifactId>
      <version>3.4.6</version>
    </dependency>
    <dependency>
      <groupId>jline</groupId>
      <artifactId>jline</artifactId>
      <version>0.9.94</version>
    </dependency>
    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.17</version>
    </dependency>
    <dependency>
      <groupId>io.netty</groupId>
      <artifactId>netty</artifactId>
      <version>3.9.4.Final</version>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>1.6.1</version>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-log4j12</artifactId>
      <version>1.6.1</version>
    </dependency>
  </dependencies>

3. 增删改查demo

zookeeper上的znode节点增删改查demo

package cn.itcast.zk;

import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import org.junit.Before;
import org.junit.Test;

import java.util.List;

/**
 * @author y15079
 * @create 2018-03-16 16:53
 * @desc  简单的增删改查demo
 **/
public class SimpleZkClient {
	private static final String connectString = "mimi1:2181,mimi2:2181,mini3:2181";
	private static final int sessionTimeout = 2000;

	ZooKeeper zkClient = null;

	@Before
	public void init() throws Exception {
		zkClient = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
			public void process(WatchedEvent watchedEvent) {
				//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）
				System.out.println(watchedEvent.getType() + "---" + watchedEvent.getPath());
				try {
					zkClient.getChildren("/", true);
				} catch (Exception e) {
				}
			}
		});
	}

	/**
	 * 数据的增删改查
	 */
	//创建数据节点到zk中
	@Test
	public  void testCreate(String[] args) throws Exception{
		//参数1，要创建的节点的路径 参数2：节点数据 参数3：节点的权限 参数4：节点的类型
		String node = zkClient.create("/idea", "hellozk".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
		//上传的数据可以是任何类型，但都要转成byte[]
	}

	//判断znode是否存在
	public void testExist() throws Exception{
		//节点元数据
		Stat stat = zkClient.exists("/idea", false);
		System.out.println(stat == null ? "not exist": "exist");
	}

	//获取子节点
	@Test
	public void getChildren() throws Exception{
		List<String> children = zkClient.getChildren("/", true);
		for (String child: children){
			System.out.println(child);
		}
		Thread.sleep(Long.MAX_VALUE);//真正运行时可以注释
	}

	//获取znode的数据
	@Test
	public void getData() throws Exception{
		byte[] data = zkClient.getData("/idea",false, null);
		System.out.println(new String(data));
	}

	//删除znode的数据
	@Test
	public void deleteZnode() throws Exception{
		//参数2：指定要删除的版本，-1表示删除所有版本
		zkClient.delete("/idea", -1);
	}

	//设置znode
	@Test
	public void setData() throws Exception{
		zkClient.setData("/app1","hello".getBytes(), -1);
		byte[] data = zkClient.getData("/app1", false, null);
		System.out.println(new String(data));
	}
}

3. Zookeeper 应用案例（分布式共享锁 ||分布式应用系统服务器上下线动态感知）

3.1 分布式共享锁的简单实现

package cn.itcast.zkclock;

import org.apache.zookeeper.*;

import java.util.Collections;
import java.util.List;
import java.util.Random;

/**
 * @author y15079
 * @create 2018-03-17 18:40
 * @desc 分布式共享锁 单线程的
 **/
public class DistributedClientLock {
	//会话超时
	private static final int SESSION_TIMEOUT = 5000;
	//zookeeper集群地址
	private String hosts = "hadoop1:2181,hadoop2:2181,hadoop3:2181";
	private String groupNode = "locks";
	private String subNode = "sub";
	private boolean haveLock = false;

	private ZooKeeper zk;
	//记录client创建的子节点路径
	private volatile String thisPath;

	/**
	 * 连接zk
	 * @throws Exception
	 */
	public void connectZookeeper() throws Exception{
		zk = new ZooKeeper(hosts, SESSION_TIMEOUT, new Watcher() {
			public void process(WatchedEvent watchedEvent) {
				try {
					//判断事件类型，此处只处理子节点变化事件
					if (watchedEvent.getType() == Event.EventType.NodeChildrenChanged && watchedEvent.getPath().equals("/" + groupNode)){
						//获取子节点，并对父节点进行监听, 开始监听，监听锁是否有变化
						List<String> childrenNodes = zk.getChildren("/" + groupNode, true);
						String thisNode = thisPath.substring(("/" + groupNode + "/").length()); //获取父目录下的子节点路径，不带父目录
						//去比较是否自己是最小id， 约定id最小最先拿到锁
						Collections.sort(childrenNodes);
						if (childrenNodes.indexOf(thisNode) == 0){  //indexOf是索引的意思，查看子节点路径在所有子节点中的索引是否为0，为0则证明子节点id最小，最先获取锁
							//访问共享资源处理业务，并且在处理完成之后删除锁
							doSomething();  //删除锁，监听到，暂时不会调用watcher里面的process方法

							//重新注册一把新的锁，不懂为什么注册新的锁
							thisPath = zk.create("/" + groupNode + "/" + subNode, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
							//在上面创建好锁后才调用watcher里面的process方法
						}
					}
				} catch (Exception e) {
				}
			}
		});

		//程序一进来就先注册一把锁到zk上，即创建子节点，还没有开始监听，zk watcher里面的process方法不会执行
		thisPath = zk.create("/" + groupNode + "/" + subNode, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);

		//wait一小会，便于观察
		Thread.sleep(new Random().nextInt(1000));

		//从zk的锁目录下，获取所有子节点，并且监听子节点的变化， 开始监听，监听锁是否有变化
		List<String> childrenNodes = zk.getChildren("/" + groupNode, true);

		//列表中只有一个子节点，那肯定就是thisPath，说明client获得锁
		if (childrenNodes.size() == 1){
			doSomething(); //删除锁，监听到，暂时不会调用watcher里面的process方法
			//为什么还创建锁？为了下一次client获取锁做好准备
			thisPath = zk.create("/" + groupNode + "/" + subNode, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
			//在上面创建好锁后才调用watcher里面的process方法
		}
	}

	/**
	 * 共享资源的访问逻辑写在这个方法中
	 * 处理业务逻辑，并释放
	 * @throws Exception
	 */
	private void doSomething() throws Exception{
		try {
			System.out.println("gain lock: " + thisPath);
			Thread.sleep(2000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}finally {
			System.out.println("finished: " + thisPath );
			//将thisPath删除，监听thisPath的client将获得通知
			//相当于释放锁
			zk.delete(this.thisPath, -1);
		}
	}

	public static void main(String[] args) throws Exception{
		DistributedClientLock dcl = new DistributedClientLock();
		dcl.connectZookeeper();
		Thread.sleep(Long.MAX_VALUE);
	}
}

3.2 分布式应用系统服务器上下线动态感知

客户端实现：

package cn.itcast.zkdist;

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

import java.util.ArrayList;
import java.util.List;

/**
 * @author y15079
 * @create 2018-03-17 15:20
 * @desc  分布式HA应用  客户端
 **/
public class DistributedClient {

	private static final String connectString = "hadoop1:2181,hadoop2:2181,hadoop3:2181";
	private static final int sessionTimeout = 2000;
	private static final String parentNode = "/servers";
	//注意：加volatile的意义何在？保持一致性
	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() {
			public void process(WatchedEvent watchedEvent) {
				//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 Exception
	 */
	public void handleBusiness() throws Exception{
		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();

		//启动业务功能
		client.handleBusiness();
	}
}

　　服务端实现：

package cn.itcast.zkdist;

import org.apache.zookeeper.*;

/**
 * @author y15079
 * @create 2018-03-17 1:12
 * @desc 分布式HA应用  服务端
 **/
public class DistributedServer {

	private static final String connectString = "hadoop1:2181,hadoop2:2181,hadoop3:2181";
	private static final int sessionTimeout = 2000;
	private static final String parentNode = "/servers";

	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() {
			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）
				System.out.println(event.getType() + "---" + event.getPath());
				try {
					zk.getChildren("/",true);
				} catch (Exception e) {
				}
			}
		});
	}

	/**
	 * 向zk集群注册服务器信息
	 * @param hostname
	 * @throws Exception
	 */
	public void registerServer(String hostname) throws Exception{
		String create = zk.create(parentNode+"server", hostname.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
		System.out.println(hostname + " is online..." + create);
	}

	/**
	 * 业务功能
	 * @throws Exception
	 */
	public void handleBusiness(String hostname) throws Exception{
		System.out.println(hostname + " start working......");
		Thread.sleep(Long.MAX_VALUE);
	}

	public static void main(String[] args) throws Exception {
		//获取zk连接
		DistributedServer server = new DistributedServer();
		server.getConnect();
		//利用zk连接注册服务器信息
		server.registerServer(args[0]);

		//启动业务功能
		server.handleBusiness(args[0]);

	}
}

github地址：

https://github.com/SwordfallYeung/Zookeeper-Java-API-Demo