ZooKeeper-znode概念与使用

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

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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

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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

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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

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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\n", groupName);
                System.exit(1);
            }
            for (String child : children) {
                System.out.println(child);
            }
        } catch (KeeperException e) {
            System.out.printf("Group %s does not exist\n", 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

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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\n", 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();
    }
     
}

　　

 

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