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HA）
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HA应用的简单实现
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/qiushangwenyue/Zookeeper-Java-API-Demo