zookeeper手把手教程（四）

2023年3月26日 275次阅读 来源: 黑白蓝调

1. 分布式应用场景

前面讲过分布式应用场景有：

  • 负载均衡
  • 分布式ID生成
  • 分布式锁
  • 分布式队列
  • 消息订阅发布
  • 命名服务
  • master选举

负载均衡

请求分摊

master选举

package com.frame.test.gp.zookeeperAPI.curator;

import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.recipes.leader.LeaderSelector;
import org.apache.curator.framework.recipes.leader.LeaderSelectorListener;
import org.apache.curator.framework.state.ConnectionState;

import java.util.concurrent.TimeUnit;

/**
 * @author Administrator
 * @CREATE 2017/8/12 20:12
 */
public class MasterSelector {

    private final static String MASTER_PATH = "/curator_master_path";

    public static void main(String[] args) {
        CuratorFramework curatorFramework = CuratorClientUtils.getInstance();
        LeaderSelector leaderSelector = new LeaderSelector(curatorFramework, MASTER_PATH, new LeaderSelectorListener() {
            @Override
            public void takeLeadership(CuratorFramework curatorFramework) throws Exception {
                System.out.println("获得leader成功");
                TimeUnit.SECONDS.sleep(2);
            }

            @Override
            public void stateChanged(CuratorFramework client, ConnectionState newState) {

            }
        });
        leaderSelector.autoRequeue();
        leaderSelector.start(); //开始选举
    }
}

消息订阅发布

实现配置信息的集中式管理和数据的动态更新,典型场景disconf

实现配置中心有两种模式：push 、pull。
长轮训
zookeeper采用的是推拉相结合的方式。 客户端向服务器端注册自己需要关注的节点。一旦节点数据发生变化，那么服务器端就会向客户端
发送watcher事件通知。客户端收到通知后，主动到服务器端获取更新后的数据

  1. 数据量比较小
  2. 数据内容在运行时会发生动态变更
  3. 集群中的各个机器共享配置

分布式ID生成

利用zookeeper中的顺序节点的特性，制作分布式的序列号生成器(ID生成器)，（在往数据库查询数据时，通常需要一个id，在单机环境下，可以利用数据库的自动成功id号，但是这种在分布式环境下就无法使用了，可以使用UUID，但是UUID有一个缺点，就是没有规律很难理解。使用zookeeper的命名服务可以生成有顺序的容易理解的，支持分布式的编号）

package com.frame.test.gp.zookeeperAPI.GenId;

import org.I0Itec.zkclient.ZkClient;
import org.I0Itec.zkclient.serialize.BytesPushThroughSerializer;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
 * @author Administrator
 * @CREATE 2017/8/13 0:16
 * 分布式ID生成器，实际上是产生持久化有序节点，然后获取有序节点，作为ID
 */
public class IdMark {
    private ZkClient zkClient;

    private final String server;  //记录服务器的地址
    private final String root;    //记录父节点的路径
    private final String nodeName;  //几点名称
    private volatile boolean runing = false;
    private ExecutorService cleanExector;

    public enum RemoveMethod {
        NONE,  //不
        IMMEDIATELY,  //立即
        DELAY   //延期
    }

    public IdMark(String server, String root, String nodeName) {
        this.server = server;
        this.root = root;
        this.nodeName = nodeName;
    }

    public void start() throws Exception {
        if (runing) {
            throw new Exception("server has started ...");
        }
        runing = true;

        init();
    }

    public void stop() throws Exception {
        if (!runing) {
            throw new Exception("server has stopped ...");
        }
        runing = false;

        freeResource();
    }

    /**
     * 初始化服务器资源
     */
    private void init() {
        zkClient = new ZkClient(server, 5000, 5000, new BytesPushThroughSerializer());
        cleanExector = Executors.newFixedThreadPool(10);
        try {
            zkClient.createPersistent(root, true);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 释放资源
     */
    private void freeResource() {
        cleanExector.shutdown();
        try {
            cleanExector.awaitTermination(2, TimeUnit.SECONDS);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            cleanExector = null;
        }
        if (zkClient != null) {
            zkClient.close();
            zkClient = null;
        }

    }

    /**
     * 检查服务是否运行
     *
     * @throws Exception
     */
    public void checkRunning() throws Exception {
        if (!runing) {
            throw new Exception("请先调用start ");
        }
    }

    private String extractId(String str) {
        int index = str.lastIndexOf(nodeName);
        if (index >= 0) {
            index += nodeName.length();
            return index <= str.length() ? str.substring(index) : "";
        }
        return str;
    }

    /**
     * 获取ID
     *
     * @param removeMethod
     * @return
     */
    public String generateId(RemoveMethod removeMethod) throws Exception {
        checkRunning();
        final String fullNodePath = root.concat("/").concat(nodeName);
        //创建顺序节点每个父节点会为他的第一级子节点维护一份时序，会记录每个子节点创建的先后顺序。
        //基于这个特性,在创建子节点的时候，可以设置这个属性,呢么在创建节点过程,
        //Zookeeper会自动为给定节点名添加后缀，作为新节点名
        final String outPath = zkClient.createPersistentSequential(fullNodePath, null);
        if (removeMethod.equals(RemoveMethod.IMMEDIATELY)) {  //立即删除
            zkClient.deleteRecursive(outPath);
        } else if (removeMethod.equals(RemoveMethod.DELAY)) { //延期删除
            cleanExector.execute(new Runnable() {
                @Override
                public void run() {
                    zkClient.delete(outPath);
                }
            });
        }
        return extractId(outPath);
    }

    public static void main(String[] args) throws Exception {
        IdMark idMaker=null;
        try {
             idMaker = new IdMark("192.168.202.133:2181,192.168.202.134:2181,192.168.202.135:2181",
                    "/NameService/IdGen", "ID-");
             idMaker.start();
            for (int i = 0; i < 2; i++) {
                String id = idMaker.generateId(RemoveMethod.DELAY);
                System.out.println(id);
            }
        }finally {
            idMaker.stop();
        }
    }
}

分布式队列生成

package com.frame.test.gp.zookeeperAPI.queue;

import org.I0Itec.zkclient.ZkClient;
import org.I0Itec.zkclient.exception.ZkNoNodeException;

import java.util.Collections;
import java.util.Comparator;
import java.util.List;

/**
 * @author Administrator
 * @CREATE 2017/8/12 19:25
 */
public class DistributedSimpleQueue<T> {
    private final ZkClient zkClient;
    private final String root;
    private static final String node_name = "n_";

    public DistributedSimpleQueue(ZkClient zkClient, String root) {
        this.zkClient = zkClient;
        this.root = root;
    }

    //获取队列的大小
    public int size() {
        //获取根节点下的所有子节点
        return zkClient.getChildren(root).size();
    }

    //判断队列是否为空
    public boolean isEmpty() {
        return size() == 0;
    }

    //存入队列
    public boolean offer(T element) {
        try {
            String nodeFullPath = root.concat("/").concat(node_name);
            zkClient.createPersistentSequential(nodeFullPath, element);
        } catch (ZkNoNodeException e) {
            zkClient.createPersistent(root);
            offer(element);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return true;
    }

    //从队列中取出元素
    public T poll() {
        try {
            List<String> list = zkClient.getChildren(root);
            if (list.size() == 0) {
                return null;
            }
            //将队列由小到大的顺序排序
            Collections.sort(list, new Comparator<String>() {
                public int compare(String lhs, String rhs) {
                    return getNodeNumber(lhs, node_name).compareTo(getNodeNumber(rhs, node_name));
                }
            });

            /**
             * 将队列中的元素做循环，然后构建完整的路径，在通过这个路径去读取数据
             */
            for (String nodeName : list) {
                String nodeFullPath = root.concat("/").concat(nodeName);
                try {
                    T node = zkClient.readData(nodeFullPath);
                    zkClient.delete(nodeFullPath);
                    return node;
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    public String getNodeNumber(String str, String nodeName) {
        int index = str.lastIndexOf(nodeName);
        if (index >= 0) {
            index += node_name.length();
            return index <= str.length() ? str.substring(index) : "";
        }
        return str;
    }
}



package com.frame.test.gp.zookeeperAPI.queue;

import com.frame.entity.Admin;
import org.I0Itec.zkclient.ZkClient;
import org.I0Itec.zkclient.serialize.SerializableSerializer;

/**
 * @author Administrator
 * @CREATE 2017/8/12 22:33
 */
public class QueueTest {
    private final static String CONNECTSTRING = "192.168.202.133:2181,192.168.202.134:2181,192.168.202.135:2181";

    public static void main(String[] args) {
        ZkClient zkClient = new ZkClient(CONNECTSTRING, 5000, 5000, new SerializableSerializer());
        zkClient.deleteRecursive("/queue");

        DistributedSimpleQueue<Admin> adminDistributedSimpleQueue = new DistributedSimpleQueue<>(zkClient, "/queue");
        for (int i = 0; i < 10; i++){
            Admin admin=new Admin();
            admin.setAdminName("队列"+i);
            admin.setAdminId((long) i);
            adminDistributedSimpleQueue.offer(admin);
            System.out.println("size: "+adminDistributedSimpleQueue.size());
        }

        Admin admin=adminDistributedSimpleQueue.poll();
        System.out.println(admin.getAdminName());
    }
}

分布式锁

package com.frame.test.gp.zookeeperAPI.javaapilock;

import com.frame.test.gp.thread.thread15.Lock;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;

import java.io.IOException;
import java.util.List;
import java.util.Random;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

/**
 * @author Administrator
 * @CREATE 2017/8/10 23:10
 */
public class DistributeLock {
    private static final String ROOT_LOCKS = "/LOCKS";  //根节点

    private ZooKeeper zooKeeper;

    private int sessionTimeOut; //会话超时时间

    private String lockID; //记录锁节点ID

    public static final byte[] data = {1, 2}; //节点数据

    public CountDownLatch countDownLatch = new CountDownLatch(1);

    public DistributeLock() throws IOException, InterruptedException {
        this.zooKeeper = ZKClientUtils.getInstance();
        this.sessionTimeOut = ZKClientUtils.getSessionTimeOut();
    }

    //获取锁的方法,有序节点最小的获得锁
    public boolean lock() {
        try {
            lockID = zooKeeper.create(ROOT_LOCKS + "/", data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);

            System.out.println(Thread.currentThread().getName() + "->成功创建了lock节点[" + lockID + "],开始竞争锁;");

            List<String> childreaNodes = zooKeeper.getChildren(ROOT_LOCKS, true); //获取根节点下的所有子节点
            //排序 从小到大
            SortedSet<String> sortedSet = new TreeSet<String>();
            for (String children : childreaNodes) {
                sortedSet.add(ROOT_LOCKS + "/" + children);
            }
            String first = sortedSet.first();
            if (lockID.equalsIgnoreCase(first)) {
                //表示当前就是最小的节点
                System.out.println(Thread.currentThread().getName() + "->成功获得锁,lock节点为:[" + lockID + "]");
                return true;
            }
            //获得锁的下一个节点 监控锁节点，当锁释放之后下一个节点获取锁
            SortedSet<String> lessThanLockId = sortedSet.headSet(lockID);  //handSet 返回从开始节点到指定元素的集合
            if (!lessThanLockId.isEmpty()) {
                String prevLockID = lessThanLockId.last(); //拿到比当前LOCKID这个节点更小的上一个节点
                zooKeeper.exists(prevLockID, new LockWatcher(countDownLatch));
                countDownLatch.await(sessionTimeOut, TimeUnit.MILLISECONDS);
                //上面这段代码意味着如果会话超时或者节点被删除(释放)
                System.out.println(Thread.currentThread().getName() + "成功获取锁:[" + lockID + "];下一个监控节点："+prevLockID);
            }
            return true;
        } catch (Exception e) {
            e.printStackTrace();
        }

        return false;
    }

    public boolean unlock() {
        System.out.println(Thread.currentThread().getName() + "->开始释放锁:[" + lockID + "]");
        try {
            zooKeeper.delete(lockID, -1);
            System.out.println("节点[" + lockID + "]成功被删除");
            return true;
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (KeeperException e) {
            e.printStackTrace();
        }
        return false;
    }

    public static void main(String[] args) {
        final CountDownLatch countDownLatch = new CountDownLatch(1);
        Random random = new Random();
        for (int i = 0; i < 10; i++) {
            new Thread(() -> {
                DistributeLock lock = null;
                try {
                    lock = new DistributeLock();
                    countDownLatch.countDown();
                    countDownLatch.await();
                    lock.lock();
                    Thread.sleep(random.nextInt(500));
                } catch (IOException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    if (lock != null) {
                        lock.unlock();
                    }
                }

            }).start();
        }
    }

}


package com.frame.test.gp.zookeeperAPI.javaapilock;

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

import java.util.concurrent.CountDownLatch;

/**
 * @author Administrator
 * @CREATE 2017/8/10 23:41
 */
public class LockWatcher implements Watcher{

    private CountDownLatch countDownLatch;

    public LockWatcher(CountDownLatch countDownLatch) {
        this.countDownLatch = countDownLatch;
    }

    @Override
    public void process(WatchedEvent watchedEvent) {
        if(watchedEvent.getType()== Event.EventType.NodeDeleted){
            countDownLatch.countDown();
        }
    }
}


package com.frame.test.gp.zookeeperAPI.javaapilock;

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

import java.io.IOException;
import java.util.concurrent.CountDownLatch;

/**
 * @author Administrator
 * @CREATE 2017/8/10 23:04
 */
public class ZKClientUtils {
    private final static String CONNECTSTRING = "192.168.202.133:2181,192.168.202.134:2181,192.168.202.135:2181";

    public static int getSessionTimeOut() {
        return sessionTimeOut;
    }

    public static final int sessionTimeOut = 5000;

    //获取链接
    public static ZooKeeper getInstance() throws IOException, InterruptedException {
        final CountDownLatch countDownLatch = new CountDownLatch(1);
        ZooKeeper zooKeeper = new ZooKeeper(CONNECTSTRING, sessionTimeOut, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                if (watchedEvent.getState()== Event.KeeperState.SyncConnected){
                    countDownLatch.countDown();
                }
            }
        });
        countDownLatch.await();
        return zooKeeper;
    }
}
    原文作者：黑白蓝调
    原文地址: https://www.jianshu.com/p/ec41cdeccee5
    本文转自网络文章，转载此文章仅为分享知识，如有侵权，请联系博主进行删除。
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