需求

客戶端感知伺服器的上下線。

示意圖

步驟

服務端：

1、所有機子向Zookeeper註冊，註冊znode為臨時的。

2、有機子下線，連線斷開後被Zookeeper自動刪除，觸發監聽事件。

3、有機子上線，觸發監聽事件。

客戶端：

1、連線Zookeeper，獲取伺服器註冊的znode，getchildren()，並註冊監聽。

2、當Zookeeper觸發監聽，會rpc遠端呼叫process。

3、process呼叫getchildren().

服務端程式碼

package hello.zookeeper.schange;

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

public class Server {

	private String connUrl = "zk1:2181,zk2:2181,zk3:2181";
	private int outTime = 1000;
	private String parentNode="/servers/";//Zookeeper先建好這個持久節點

	private ZooKeeper zk = null;

	public void getConnection() throws Exception {

		zk = new ZooKeeper(connUrl, outTime, new Watcher() {

			@Override
			public void process(WatchedEvent event) {
				System.out.println("Server Watcher：" + event.getType() + "---" + event.getPath());
			}
		});
	}

	public void registerServer(String server) throws Exception {
		String msg = zk.create(parentNode+server, server.getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
		System.out.println("registerServer：" + msg);
	}

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

		String name = "server4";
		Server server = new Server();
		server.getConnection();
		server.registerServer(name);

		System.out.println(name + "----start------");

		Thread.sleep(Long.MAX_VALUE);
	}

}
 

客戶端程式碼

package hello.zookeeper.schange;

import java.util.List;

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

public class Client {
	
	private String connUrl = "zk1:2181,zk2:2181,zk3:2181";
	private int outTime = 1000;
	private String parentNode="/servers";

	private ZooKeeper zk = null;

	public void getConnection() throws Exception {

		zk = new ZooKeeper(connUrl, outTime, new Watcher() {

			@Override
			public void process(WatchedEvent event) {
				System.out.println("Client Watcher：" + event.getType() + "---" + event.getPath());
				try {
					getServerList();
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}
	
	
	public void getServerList() throws Exception{
		
		List<String> children = zk.getChildren(parentNode, true);
		if(children!=null&&children.size()>0){
			System.out.println("伺服器列表如下：");
			for(String child:children){
				System.out.println(child);
			}
		}
	}
	
	
	public static void main(String[] args) throws Exception {
		Client client=new Client();
		client.getConnection();
		client.getServerList();
		
		Thread.sleep(Long.MAX_VALUE);
	}
	
	
}
 

執行結果

開了4臺服務端，3臺客戶端

Zookeeper裡/servers節點下有4臺註冊線上的伺服器

客戶端執行獲取服務端列表

伺服器下線一臺，三個客戶端都受到通知

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