可以将ZK看作一个具有高可用性特征的文件系统。这个文件系统中没有文件和目录，而是统一使用节点（znode）的概念，称为znode。znode既可以作为保存数据的容器（如同文件），也可以作为保存其他znode的容器（如同目录）。所有的znode构成了一个层次化的命名空间，一种自然的建立组成员列表的方式就是利用这种层次结构，创建一个以组名为节点名的znode作为父节点，然后以组成员名（服务器名）为节点名来创建作为子节点的znode。
创建组
package com.zhen.zookeeper.createGroup;
import java.io.IOException;
import java.util.concurrent.CountDownLatch;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
/**
* @author FengZhen
* @date 2018年10月13日
* 创建组
*/
public class CreateGroup implements Watcher{
private static final int SESSION_TIMEOUT = 5000;
private ZooKeeper zk;
private CountDownLatch connectedSignal = new CountDownLatch(1);
public void connect(String hosts) throws IOException, InterruptedException {
/**
* hosts:ZooKeeper服务的主机地址（可指定端口，默认是2181）
* SESSION_TIMEOUT:以毫秒为单位的会话超时参数（此处为5秒）
* this:Watcher对象的实例。Watcher对象接收来自于ZooKeeper的回调，以获得各种事件的通知。
*/
zk = new ZooKeeper(hosts, SESSION_TIMEOUT, this);
connectedSignal.await();
}
/**
* 当客户端已经与ZK建立连接后，Watcher的process方法会被调用
* 参数是一个用于表示该连接的事件。
*/
public void process(WatchedEvent event) {
//连接事件
if (event.getState() == KeeperState.SyncConnected) {
/**
* 通过调用CountDownLatch的countDown方法来递减它的计数器。
* 锁存器（latch）被创建时带有一个值为1的计数器，用于表示在它释放所有等待线程之前需要发生的事件数。
* 在调用一次countDown方法之后，计数器的值变为0，则await方法返回。
*/
connectedSignal.countDown();
}
}
public void create(String groupName) throws KeeperException, InterruptedException {
String path = "/" + groupName;
/**
* 用ZK的create方法创建一个新的ZK的znode
* path：路径（用字符串表示）
* null：znode的内容（字节数组，此处为空值）
* Ids.OPEN_ACL_UNSAFE：访问控制列表(简称ACL，此处为完全开放的ACL，允许任何客户端对znode进行读写)
* CreateMode.PERSISTENT：znode类型
* znode类型可以分为两种：1.短暂的(ephemeral) 2.持久的(persistent)
* 创建znode的客户端断开连接时，无论客户端是明确断开还是因为任何原因而终止，短暂znode都会被ZK服务删除。持久znode不会被删除。
* create方法的返回值是ZK所创建的节点路径
*/
String createdPath = zk.create(path, null, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
System.out.println("Created " + createdPath);
}
public void close() throws InterruptedException {
zk.close();
}
public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
String hosts = "localhost:2181";
String groupName = "zoo";
CreateGroup createGroup = new CreateGroup();
createGroup.connect(hosts);
createGroup.create(groupName);
createGroup.close();
}
}
提供一个连接类
package com.zhen.zookeeper;
import java.io.IOException;
import java.util.concurrent.CountDownLatch;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.Watcher.Event.KeeperState;
/**
* @author FengZhen
* @date 2018年10月13日
* 等待与ZK建立连接
*/
public class ConnectionWatcher implements Watcher{
private static final int SESSION_TIMEOUT = 5000;
protected ZooKeeper zk;
private CountDownLatch connectedSignal = new CountDownLatch(1);
public void connect(String hosts) throws IOException, InterruptedException {
/**
* hosts:ZooKeeper服务的主机地址（可指定端口，默认是2181）
* SESSION_TIMEOUT:以毫秒为单位的会话超时参数（此处为5秒）
* this:Watcher对象的实例。Watcher对象接收来自于ZooKeeper的回调，以获得各种事件的通知。
*/
zk = new ZooKeeper(hosts, SESSION_TIMEOUT, this);
connectedSignal.await();
}
/**
* 当客户端已经与ZK建立连接后，Watcher的process方法会被调用
* 参数是一个用于表示该连接的事件。
*/
public void process(WatchedEvent event) {
//连接事件
if (event.getState() == KeeperState.SyncConnected) {
/**
* 通过调用CountDownLatch的countDown方法来递减它的计数器。
* 锁存器（latch）被创建时带有一个值为1的计数器，用于表示在它释放所有等待线程之前需要发生的事件数。
* 在调用一次countDown方法之后，计数器的值变为0，则await方法返回。
*/
connectedSignal.countDown();
}
}
public void close() throws InterruptedException {
zk.close();
}
}
加入组
package com.zhen.zookeeper.joinGroup;
import java.io.IOException;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.ZooDefs.Ids;
import com.zhen.zookeeper.ConnectionWatcher;
/**
* @author FengZhen
* @date 2018年10月13日
* 加入组-注册组成员
*/
public class JoinGroup extends ConnectionWatcher{
public void join(String groupName, String memberName) throws KeeperException, InterruptedException {
String path = "/" + groupName + "/" + memberName;
//创建短暂znode作为组znode的子节点
String createdPath = zk.create(path, null, Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("Created " + createdPath);
}
public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
String hosts = "localhost:2181";
String groupName = "zoo";
String memberName = "member1";
JoinGroup joinGroup = new JoinGroup();
joinGroup.connect(hosts);
joinGroup.join(groupName, memberName);
Thread.sleep(Long.MAX_VALUE);
}
/**
* echo dump | nc localhost 2181
SessionTracker dump:
Session Sets (3):
0 expire at Sat Oct 13 15:57:48 CST 2018:
0 expire at Sat Oct 13 15:57:50 CST 2018:
1 expire at Sat Oct 13 15:57:52 CST 2018:
0x166594274c90001
ephemeral nodes dump:
Sessions with Ephemerals (1):
0x166594274c90001:
/zoo/member1
*/
}
列出组成员
package com.zhen.zookeeper.listGroup;
import java.io.IOException;
import java.util.List;
import org.apache.zookeeper.KeeperException;
import com.zhen.zookeeper.ConnectionWatcher;
/**
* @author FengZhen
* @date 2018年10月13日
* 列出组成员
*/
public class ListGroup extends ConnectionWatcher{
public void list(String groupName) {
String path = "/" + groupName;
try {
/**
* 输出一个znode的子节点列表
* path：该znode的路径
* false:观察标志
* 如果在一个znode上设置了观察标志，那么一旦该znode的状态改变，关联的观察（Watcher）会被触发。
* 虽然此处没有使用观察，但在查看一个znode的子节点时，通过设置观察可以让应用程序接收到组成员加入、退出和组被删除的有关通知
*/
List<String> children = zk.getChildren(path, false);
if (children.isEmpty()) {
System.out.printf("No members in group %s
", groupName);
System.exit(1);
}
for (String child : children) {
System.out.println(child);
}
} catch (KeeperException e) {
System.out.printf("Group %s does not exist
", groupName);
System.exit(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws IOException, InterruptedException {
String hosts = "localhost:2181";
String groupName = "zoo";
ListGroup listGroup = new ListGroup();
listGroup.connect(hosts);
listGroup.list(groupName);
listGroup.close();
}
/**
* 也可使用命令行工具
* ./zkCli.sh -server localhost:2181 ls /zoo
* Connecting to localhost:2181
2018-10-13 16:26:10,856 [myid:] - INFO [main:Environment@100] - Client environment:zookeeper.version=3.4.9-1757313, built on 08/23/2016 06:50 GMT
2018-10-13 16:26:10,860 [myid:] - INFO [main:Environment@100] - Client environment:host.name=192.168.1.109
2018-10-13 16:26:10,860 [myid:] - INFO [main:Environment@100] - Client environment:java.version=1.8.0_162
2018-10-13 16:26:10,863 [myid:] - INFO [main:Environment@100] - Client environment:java.vendor=Oracle Corporation
2018-10-13 16:26:10,863 [myid:] - INFO [main:Environment@100] - Client environment:java.home=/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre
2018-10-13 16:26:10,863 [myid:] - INFO [main:Environment@100] - Client environment:java.class.path=/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin/../build/classes:/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin/../build/lib/*.jar:/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin/../lib/slf4j-log4j12-1.6.1.jar:/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin/../lib/slf4j-api-1.6.1.jar:/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin/../lib/netty-3.10.5.Final.jar:/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin/../lib/log4j-1.2.16.jar:/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin/../lib/jline-0.9.94.jar:/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin/../zookeeper-3.4.9.jar:/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin/../src/java/lib/*.jar:/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin/../conf:
2018-10-13 16:26:10,863 [myid:] - INFO [main:Environment@100] - Client environment:java.library.path=/Users/FengZhen/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.
2018-10-13 16:26:10,863 [myid:] - INFO [main:Environment@100] - Client environment:java.io.tmpdir=/var/folders/tr/vc5hfpsd2c56s7m9wh93401h0000gn/T/
2018-10-13 16:26:10,863 [myid:] - INFO [main:Environment@100] - Client environment:java.compiler=<NA>
2018-10-13 16:26:10,863 [myid:] - INFO [main:Environment@100] - Client environment:os.name=Mac OS X
2018-10-13 16:26:10,864 [myid:] - INFO [main:Environment@100] - Client environment:os.arch=x86_64
2018-10-13 16:26:10,864 [myid:] - INFO [main:Environment@100] - Client environment:os.version=10.13.4
2018-10-13 16:26:10,864 [myid:] - INFO [main:Environment@100] - Client environment:user.name=FengZhen
2018-10-13 16:26:10,864 [myid:] - INFO [main:Environment@100] - Client environment:user.home=/Users/FengZhen
2018-10-13 16:26:10,864 [myid:] - INFO [main:Environment@100] - Client environment:user.dir=/Users/FengZhen/Desktop/Hadoop/zookeeper-3.4.9/bin
2018-10-13 16:26:10,865 [myid:] - INFO [main:ZooKeeper@438] - Initiating client connection, connectString=localhost:2181 sessionTimeout=30000 watcher=org.apache.zookeeper.ZooKeeperMain$MyWatcher@799f7e29
2018-10-13 16:26:10,898 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1032] - Opening socket connection to server localhost/0:0:0:0:0:0:0:1:2181. Will not attempt to authenticate using SASL (unknown error)
2018-10-13 16:26:11,014 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@876] - Socket connection established to localhost/0:0:0:0:0:0:0:1:2181, initiating session
2018-10-13 16:26:11,024 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1299] - Session establishment complete on server localhost/0:0:0:0:0:0:0:1:2181, sessionid = 0x166594274c90006, negotiated timeout = 30000
WATCHER::
WatchedEvent state:SyncConnected type:None path:null
[member1]
*/
}
删除组
package com.zhen.zookeeper.deleteGroup;
import java.io.IOException;
import java.util.List;
import org.apache.zookeeper.KeeperException;
import com.zhen.zookeeper.ConnectionWatcher;
/**
* @author FengZhen
* @date 2018年10月13日
* 删除组
*
*/
public class DeleteGroup extends ConnectionWatcher{
public void delete(String groupName) {
String path = "/" + groupName;
try {
List<String> children = zk.getChildren(path, false);
for (String child : children) {
zk.delete(path + "/" + child, -1);
}
/**
* delete方法有两个参数
* path：节点路径
* -1：版本号
* 如果所提供的版本号与znode的版本号一致，ZK会删除这个znode。
* 这是一种乐观的加锁机制，使客户端能够检测出对znode的修改冲突。
* 通过将版本号设置为-1，可以绕过这个版本检测机制，不管znode的版本号是什么而直接将其删除。
* ZK不支持递归删除，因此在删除父节点之前必须先删除子节点
*/
zk.delete(path, -1);
} catch (KeeperException e) {
System.out.printf("Group %s does not exist
", groupName);
System.exit(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws IOException, InterruptedException {
String hosts = "localhost:2181";
String groupName = "zoo";
DeleteGroup deleteGroup = new DeleteGroup();
deleteGroup.connect(hosts);
deleteGroup.delete(groupName);
deleteGroup.close();
}
}