Zookeeper：实现“通知协调”的 Demo

小鱼儿 2023-09-23 15:57 94阅读 0赞

> 应用配置集中到节点上，应用启动时主动获取，并在节点上注册一个 watcher，每次配置更新都会通知到应用。数据发布/订阅（Publish/Subscribe）系统，即所谓的配置中心，顾名思义就是发布者将数据发布到 ZooKeeper 的一个或一系列节点上，供订阅者进行数据订阅，进而达到动态获取数据的目的，实现配置信息的集中式管理和数据的动态更新。
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> 本篇内容包括：Demo 概述、代码实现、测试结果

--------------------

### 文章目录 ###

*   *  一、Demo 概述
     *   *   *  1、关于 zookeeper “通知协调”
             *  2、Demo 设计
             *  3、Demo 前提
     *  二、代码实现
     *   *   *  1、引用 Maven 依赖
             *  2、ConnectionWatcher 类创建 Zookeeper 连接
             *  3、ActiveKeyValueStore 类读写 Zookeeper 数据
             *  4、ConfigUpdater 类发布数据信息
             *  5、ConfigWatcher 类订阅数据信息
     *  三、测试结果
     *   *   *  1、ConfigUpdater 打印内容
             *  2、ConfigWatcher 打印内容

--------------------

## 一、Demo 概述 ##

#### 1、关于 zookeeper “通知协调” ####

应用配置集中到节点上，应用启动时主动获取，并在节点上注册一个 watcher，每次配置更新都会通知到应用。

数据发布/订阅（Publish/Subscribe）系统，即所谓的配置中心，顾名思义就是发布者将数据发布到 ZooKeeper 的一个或一系列节点上，供订阅者进行数据订阅，进而达到动态获取数据的目的，实现配置信息的集中式管理和数据的动态更新。

#### 2、Demo 设计 ####

采用发布/订阅模式将配置信息发布到 Zookeeper 节点上，供订阅者动态获取数据：

![Zookeeper订阅发布Demo][Zookeeper_Demo]

1.  首先需要启动 Zookeeper 服务，规划集群配置信息存放的节点 /config;
2.  然后通过 ConfigWatcher 类更新 /config 节点注册监视器 watcher，监控集群配置信息变化;
3.  最后通过 ConfigUpdater 类不断更新 /config 节点配置信息，从而模拟实现集群配置信息订阅发布效果。

#### 3、Demo 前提 ####

参考：[Mac通过Docker安装Zookeeper集群][Mac_Docker_Zookeeper]

--------------------

## 二、代码实现 ##

#### 1、引用 Maven 依赖 ####

<dependency>
                <groupId>org.apache.zookeeper</groupId>
                <artifactId>zookeeper</artifactId>
                <version>3.7.0</version>
            </dependency>

#### 2、ConnectionWatcher 类创建 Zookeeper 连接 ####

import java.io.IOException;
    import java.util.concurrent.CountDownLatch;
    
    import org.apache.zookeeper.WatchedEvent;
    import org.apache.zookeeper.Watcher;
    import org.apache.zookeeper.ZooKeeper;
    
    public class ConnectionWatcher implements Watcher {
        
    
        private final CountDownLatch connectedSignal = new CountDownLatch(1);
        private static final int SESSION_TIMEOUT = 5000;
        protected ZooKeeper zk;
    
    
        public void connect(String hosts) throws IOException, InterruptedException {
        
            zk = new ZooKeeper(hosts, SESSION_TIMEOUT, this);
            connectedSignal.await();
        }
    
        @Override
        public void process(WatchedEvent event) {
        
            if (event.getState() == Event.KeeperState.SyncConnected) {
        
                connectedSignal.countDown();
            }
        }
    
        public void close() throws InterruptedException {
        
            zk.close();
        }
    
    }

#### 3、ActiveKeyValueStore 类读写 Zookeeper 数据 ####

import java.nio.charset.Charset;
    import java.nio.charset.StandardCharsets;
    import java.util.List;
    
    import org.apache.zookeeper.CreateMode;
    import org.apache.zookeeper.KeeperException;
    import org.apache.zookeeper.Watcher;
    import org.apache.zookeeper.ZooDefs;
    import org.apache.zookeeper.data.Stat;
    
    public class ActiveKeyValueStore extends ConnectionWatcher {
        
    
        private static final Charset CHARSET = StandardCharsets.UTF_8;
    
        /**
         * 读取节点数据
         *
         * @param path  节点地址
         * @param value 数据值
         * @throws InterruptedException 中断异常
         * @throws KeeperException ZooKeeper异常
         */
        public void write(String path, String value) throws InterruptedException, KeeperException {
        
            Stat stat = zk.exists(path, false);
            if (stat == null) {
        
                if (value == null) {
        
                    zk.create(path, null,
                            ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
                } else {
        
                    zk.create(path, value.getBytes(CHARSET),
                            ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
                }
    
            } else {
        
                if (value == null) {
        
                    zk.setData(path, null, -1);
                } else {
        
                    zk.setData(path, value.getBytes(CHARSET), -1);
                }
    
            }
        }
    
        /**
         * 读取节点数据
         *
         * @param path 节点地址
         * @param watcher watcher
         * @return 数据值
         * @throws InterruptedException 中断异常
         * @throws KeeperException ZooKeeper异常
         */
        public String read(String path, Watcher watcher) throws InterruptedException, KeeperException {
        
            /* stat */
            byte[] data = zk.getData(path, watcher, null);
            return new String(data, CHARSET);
        }
    }

#### 4、ConfigUpdater 类发布数据信息 ####

import java.io.IOException;
    import java.util.Random;
    import java.util.concurrent.TimeUnit;
    
    import org.apache.zookeeper.KeeperException;
    
    public class ConfigUpdater {
        
        public static final String PATH = "/configuration";
        private final ActiveKeyValueStore store;
        private final Random random = new Random();
    
        public ConfigUpdater(String hosts) throws IOException, InterruptedException {
        
            //定义一个类
            store = new ActiveKeyValueStore();
            //连接Zookeeper
            store.connect(hosts);
        }
    
        public void run() throws InterruptedException, KeeperException {
        
            // noinspection InfiniteLoopStatement
            while (true) {
        
                String value = random.nextInt(100) + "";
                //向 ZNode 写数据（也可以将xml文件写进去）
                store.write(PATH, value);
                System.out.printf("Set %s to %s\n", PATH, value);
                TimeUnit.SECONDS.sleep(random.nextInt(10));
            }
        }
    
        public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        
            String hosts = "localhost:2181";
            ConfigUpdater updater = new ConfigUpdater(hosts);
            updater.run();
        }
    }

#### 5、ConfigWatcher 类订阅数据信息 ####

import java.io.IOException;
    
    import org.apache.zookeeper.KeeperException;
    import org.apache.zookeeper.WatchedEvent;
    import org.apache.zookeeper.Watcher;
    
    public class ConfigWatcher implements Watcher {
        
        private final ActiveKeyValueStore store;
    
        public ConfigWatcher(String hosts) throws InterruptedException, IOException {
        
            store = new ActiveKeyValueStore();
            //连接Zookeeper
            store.connect(hosts);
        }
    
        public void displayConfig() throws InterruptedException, KeeperException {
        
            String value = store.read(ConfigUpdater.PATH, this);
            System.out.printf("Read %s as %s\n", ConfigUpdater.PATH, value);
    
        }
    
        @Override
        public void process(WatchedEvent event) {
        
            System.out.printf("Process incoming event: %s\n", event.toString());
            if (event.getType() == Event.EventType.NodeDataChanged) {
        
                try {
        
                    displayConfig();
                } catch (InterruptedException e) {
        
                    System.err.println("Interrupted. Exiting");
                    Thread.currentThread().interrupt();
                } catch (KeeperException e) {
        
                    System.err.printf("KeeperException: %s. Exiting.\n", e);
                }
            }
        }
    
        public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        
            String hosts = "localhost:2181";
            //创建 watcher
            ConfigWatcher watcher = new ConfigWatcher(hosts);
            //调用 display 方法
            watcher.displayConfig();
            //然后一直处于监控状态
            Thread.sleep(Long.MAX_VALUE);
        }
    }

--------------------

## 三、测试结果 ##

#### 1、ConfigUpdater 打印内容 ####

Set /configuration to 76
    Set /configuration to 55
    Set /configuration to 13
    ...

#### 2、ConfigWatcher 打印内容 ####

Read /configuration as 76
    Read /configuration as 55
    Read /configuration as 13
    ...

通过 ConfigUpdater 发布的信息以及 ConfigWatcher 监控得到的信息可以看出，已经成功模拟实现集群配置信息的订阅发布

[Zookeeper_Demo]: https://lizhengi.oss-cn-beijing.aliyuncs.com/BenjaminNode/%E6%9C%AA%E5%91%BD%E5%90%8D%E6%96%87%E4%BB%B6%20%286%29.png
[Mac_Docker_Zookeeper]: https://blog.csdn.net/weixin_45187434/article/details/127958888