Zookeeper：实现“通知协调”的 Demo
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。 ～ 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”
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
- 首先需要启动 Zookeeper 服务，规划集群配置信息存放的节点 /config;
- 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;
- 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
二、代码实现
1、引用 Maven 依赖
<!-- 选择对应的Zookeeper版本 -->
<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
本文参与 腾讯云自媒体同步曝光计划，分享自作者个人站点/博客。
原始发表：2022-11-21，如有侵权请联系 cloudcommunity@tencent.com 删除
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