Zookeeper 文档

Zookeeper 是一个开源的分布式应用程序协调服务，它主要用于处理分布式应用程序中的配置管理、命名服务、分布式锁和集群管理等功能。

安装与配置

安装

1. 下载 Zookeeper 安装包。
2. 解压安装包到指定目录。
3. 修改 conf/zoo_sample.cfg 文件，配置 Zookeeper 的相关参数。

配置

• dataDir: 数据存储目录。
• clientPort: 客户端连接端口。
• maxClientCnxns: 最大客户端连接数。

常用命令

• start: 启动 Zookeeper 服务。
• stop: 停止 Zookeeper 服务。
• status: 查看 Zookeeper 服务状态。

示例

以下是一个简单的示例，演示如何使用 Zookeeper 实现分布式锁。

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

public class DistributedLock implements Watcher {

    private ZooKeeper zk;
    private String root = "/locks";
    private String lockName = "lock";
    private String myZnode;

    public DistributedLock(String hosts) throws IOException, KeeperException, InterruptedException {
        zk = new ZooKeeper(hosts, 3000, this);
        // 创建锁的根节点
        if (zk.exists(root, false) == null) {
            zk.create(root, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        }
    }

    public void acquireLock() throws KeeperException, InterruptedException {
        String znode = root + "/" + lockName;
        myZnode = zk.create(znode, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        List<String> children = zk.getChildren(root, false);
        Collections.sort(children);
        String sequence = myZnode.substring(myZnode.lastIndexOf('/') + 1);
        int index = children.indexOf(sequence);
        if (index == 0) {
            System.out.println("Lock acquired");
        } else {
            String predecessor = children.get(index - 1);
            Stat stat = zk.exists(predecessor, this);
            if (stat != null) {
                zk.getData(predecessor, this, stat);
            }
        }
    }

    public void processWait() throws KeeperException, InterruptedException {
        synchronized (this) {
            this.wait();
        }
    }

    public void processDone() {
        try {
            zk.delete(myZnode, -1);
            System.out.println("Lock released");
        } catch (InterruptedException | KeeperException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void process(WatchedEvent watchedEvent) throws InterruptedException {
        if (Event.KeeperState.SyncConnected == watchedEvent.getState()) {
            if (Event.EventType.NodeData == watchedEvent.getType()) {
                synchronized (this) {
                    this.notifyAll();
                }
            }
        }
    }

    public static void main(String[] args) throws IOException, KeeperException, InterruptedException {
        DistributedLock lock = new DistributedLock("127.0.0.1:2181");
        lock.acquireLock();
        lock.processWait();
        lock.processDone();
    }
}

扩展阅读

更多关于 Zookeeper 的内容，请访问 Zookeeper 官方文档。

Zookeeper