需求

客戶端感知服務器的上下線。

示意圖

步驟

服務端：

1、所有機子向Zookeeper注冊，注冊znode為臨時的。

2、有機子下線，連接斷開后被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、連接Zookeeper，獲取服務器注冊的znode，getchildren()，并注冊監聽。

2、當Zookeeper觸發監聽，會rpc遠程調用process。

3、process調用getchildren().

服務端代碼

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() {@Overridepublic 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);}}

客戶端代碼

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() {@Overridepublic 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("服務器列表如下：");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);}}

運行結果

開了4臺服務端，3臺客戶端

Zookeeper里/servers節點下有4臺注冊在線的服務器

客戶端運行獲取服務端列表

服務器下線一臺，三個客戶端都受到通知

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