zookeeper分布式集群中基于Curator实现单点设备上线下线心跳感知系统（二）

假设该设备A处于分布式集群中，且需要实时感知分布式集群中其他设备的上线、下线，存活状态：

import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.cache.*;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.data.Stat;


public class Main {
    private String DEVICE_PATH = "/devices";

    public static void main(String[] args) {
        //初始化log4j，zookeeper否则报错。
        //org.apache.log4j.BasicConfigurator.configure();

        try {
            Main m = new Main();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private String getAddress() {
        String ip = "127.0.0.1";
        return ip + ":2181," + ip + ":2182," + ip + ":2183";
    }

    public Main() throws Exception {
        RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 5);
        CuratorFramework client = CuratorFrameworkFactory.builder()
                .connectString(getAddress())
                .sessionTimeoutMs(20 * 1000)
                .connectionTimeoutMs(20 * 1000)
                .retryPolicy(retryPolicy)
                .build();

        client.start();


        //检测是否存在该路径。
        Stat stat = client.checkExists().forPath(DEVICE_PATH);

        //如果不存在这个路径，stat为null，创建新的节点路径。
        if (stat == null) {
            String s = client.create()
                    .creatingParentsIfNeeded()
                    .withMode(CreateMode.PERSISTENT)
                    .forPath(DEVICE_PATH);

            System.out.println("已创建:" + s);
        } else {
            System.out.println("已存在:" + DEVICE_PATH);
        }

        TreeCache treeCache = new TreeCache(client, DEVICE_PATH);
        TreeCacheListener treeCacheListener = new TreeCacheListener() {
            @Override
            public void childEvent(CuratorFramework client, TreeCacheEvent event) throws Exception {
                System.out.println("-----");
                System.out.println("路径:" + event.getData().getPath());
                System.out.println("数据:" + new String(event.getData().getData(), "UTF-8"));

                System.out.println("ZooKeeper:" + client.getZookeeperClient().getZooKeeper().toString());
            }
        };

        treeCache.getListenable().addListener(treeCacheListener);
        treeCache.start();

        synchronized (this) {
            wait();
        }
    }
}

下面这个设备B模拟一个普通设备接入分布式集群中：

import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.zookeeper.CreateMode;


public class Main {
    private String DEVICE_PATH = "/devices";

    public static void main(String[] args) {
        //初始化log4j，zookeeper否则报错。
        //org.apache.log4j.BasicConfigurator.configure();

        try {
            Main app = new Main();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public Main() throws Exception {
        RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 5);
        CuratorFramework client = CuratorFrameworkFactory.builder()
                .connectString(getAddress())
                .sessionTimeoutMs(20 * 1000)
                .connectionTimeoutMs(20 * 1000)
                .retryPolicy(retryPolicy)
                .build();

        client.start();


        String s = client.create()
                .creatingParentsIfNeeded()
                .withMode(CreateMode.EPHEMERAL_SEQUENTIAL)
                .forPath(DEVICE_PATH + "/client");

        System.out.println("已创建:" + s);

        synchronized (this) {
            wait();
        }
    }

    private String getAddress() {
        String ip = "127.0.0.1";
        return ip + ":2181," + ip + ":2182," + ip + ":2183";
    }
}

设备A和设备B均针对/devices作为node path监听。