Zookeeper应用：服务端上下线
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() {
@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() {
@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("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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