Zookeeper应用：服务端上下线

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需求

客户端感知服务器的上下线。

示意图

步骤

服务端：

1、所有机子向Zookeeper注册，注册znode为临时的。

2、有机子下线，连接断开后被Zookeeper自动删除，触发监听事件。

3、有机子上线，触发监听事件。

客户端：

1、连接Zookeeper，获取服务器注册的znode，getchildren()，并注册监听。

2、当Zookeeper触发监听，会rpc远程调用process。

3、process调用getchildren().

服务端代码

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先建好这个持久节点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);}}

客户端代码

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("服务器列表如下：");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);}}

运行结果

开了4台服务端，3台客户端

Zookeeper里/servers节点下有4台注册在线的服务器

客户端运行获取服务端列表

服务器下线一台，三个客户端都受到通知

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