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。
2．需求分析，如图所示
3．具体实现
（0）先在集群上创建/servers节点
[zk: localhost:2181(CONNECTED) 10] create /servers “servers”
Created /servers
（1）服务器端向Zookeeper注册代码
package com.atguigu.zkcase;
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]);
}
}
（2）客户端代码
package com.atguigu.zkcase;
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();
}
}
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