第4章 服务器动态上下线监听案例

第4章 服务器动态上下线监听案例

4.1 需求

某分布式系统中，主节点可以有多台，可以动态上下线，任意一台客户端都能实时感知到主节点服务器的上下线。

4.2 需求分析

4.3 具体实现

（1）先在集群上创建/servers节点

[zk: localhost:2181(CONNECTED) 10] create /servers "servers"
Created /servers

（2）在Idea中创建包名：com.wolffy.zookeeper.zkapplication

（3）服务器端向Zookeeper注册代码

package com.wolffy.zookeeper.zkapplication;

import java.io.IOException;

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

public class DistributeServer {

    private static String connectString = "hadoop102:2181,hadoop103:2181,hadoop104:2181";
    private static int sessionTimeout = 2000;
    private ZooKeeper zk = null;
    private String parentNode = "/servers";

    // 创建到zk的客户端连接
    public void getConnect() throws IOException {

        zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {

            @Override
            public void process(WatchedEvent event) {

            }
        });
    }

    // 注册服务器
    public void registServer(String hostname) throws Exception {

        String create = zk.create(parentNode + "/server", hostname.getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);

        System.out.println(hostname + " is online " + create);
    }

    // 业务功能
    public void business(String hostname) throws Exception {
        System.out.println(hostname + " is working ...");

        Thread.sleep(Long.MAX_VALUE);
    }

    public static void main(String[] args) throws Exception {

        // 1获取zk连接
        DistributeServer server = new DistributeServer();
        server.getConnect();

        // 2 利用zk连接注册服务器信息
        server.registServer(args[0]);

        // 3 启动业务功能
        server.business(args[0]);
    }
}

（3）客户端代码

package com.wolffy.zookeeper.zkapplication;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

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

public class DistributeClient {

    private static String connectString = "hadoop102:2181,hadoop103:2181,hadoop104:2181";
    private static int sessionTimeout = 2000;
    private ZooKeeper zk = null;
    private String parentNode = "/servers";

    // 创建到zk的客户端连接
    public void getConnect() throws IOException {

        zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {

            @Override
            public void process(WatchedEvent event) {

                // 再次启动监听
                try {
                    getServerList();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    // 获取服务器列表信息
    public void getServerList() throws Exception {

        // 1获取服务器子节点信息，并且对父节点进行监听
        List<String> children = zk.getChildren(parentNode, true);

        // 2存储服务器信息列表
        ArrayList<String> servers = new ArrayList<>();

        // 3遍历所有节点，获取节点中的主机名称信息
        for (String child : children) {
            byte[] data = zk.getData(parentNode + "/" + child, false, null);

            servers.add(new String(data));
        }

        // 4打印服务器列表信息
        System.out.println(servers);
    }

    // 业务功能
    public void business() throws Exception {

        System.out.println("client is working ...");
        Thread.sleep(Long.MAX_VALUE);
    }

    public static void main(String[] args) throws Exception {

        // 1获取zk连接
        DistributeClient client = new DistributeClient();
        client.getConnect();

        // 2获取servers的子节点信息，从中获取服务器信息列表
        client.getServerList();

        // 3业务进程启动
        client.business();
    }
}

4.4 测试

1）在Linux命令行上操作增加减少服务器

（1）启动DistributeClient客户端

（2）在hadoop102上zk的客户端/servers目录上创建临时带序号节点

[zk: localhost:2181(CONNECTED) 1] create -e -s /servers/hadoop102 "hadoop102"
[zk: localhost:2181(CONNECTED) 2] create -e -s /servers/hadoop103 "hadoop103"

（3）观察Idea控制台变化

[hadoop102, hadoop103]

​ （4）执行删除操作

[zk: localhost:2181(CONNECTED) 8] delete /servers/server0000000000

（5）观察Idea控制台变化

[hadoop103]

2）在Idea上操作增加减少服务器

（1）启动DistributeClient客户端（如果已经启动过，不需要重启）

（2）启动DistributeServer服务

​ ①点击Edit Configurations…

​ ②在弹出的窗口中（Program arguments）输入想启动的主机，例如，hadoop102

标签：String,zk,zookeeper,监听,servers,案例,import,服务器,public
来源： https://www.cnblogs.com/niuniu2022/p/16342482.html