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
package cn.com.toto.zkonlineoroffline;
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 DistributedClient {
private static final String connectString = "192.168.106.80:2181,192.168.106.81:2181,192.168.106.82:2181";
private static final int sessionTimeout = 2000;
private static final String parentNode = "/servers";
// 注意:加volatile的意义何在？
private volatile List<String> serverList;
private ZooKeeper zk = null;
/**
* 创建到zk的客户端连接
*
* @throws Exception
*/
public void getConnect() throws Exception {
zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
@Override
public void process(WatchedEvent event) {
// 收到事件通知后的回调函数（应该是我们自己的事件处理逻辑）
try {
//重新更新服务器列表，并且注册了监听
getServerList();
} catch (Exception e) {
}
}
});
}
/**
* 获取服务器信息列表
*
* @throws Exception
*/
public void getServerList() throws Exception {
// 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);
// 先创建一个局部的list来存服务器信息
List<String> servers = new ArrayList<String>();
for (String child : children) {
// child只是子节点的节点名
byte[] data = zk.getData(parentNode + "/" + child, false, null);
servers.add(new String(data));
}
// 把servers赋值给成员变量serverList，已提供给各业务线程使用
serverList = servers;
//打印服务器列表
System.out.println(serverList);
}
/**
* 业务功能
*
* @throws InterruptedException
*/
public void handleBussiness() throws InterruptedException {
System.out.println("client start working.....");
Thread.sleep(Long.MAX_VALUE);
}
public static void main(String[] args) throws Exception {
// 获取zk连接
DistributedClient client = new DistributedClient();
client.getConnect();
// 获取servers的子节点信息（并监听），从中获取服务器信息列表
client.getServerList();
// 业务线程启动
client.handleBussiness();
}
}
package cn.com.toto.zkonlineoroffline;
import java.util.concurrent.CountDownLatch;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.data.Stat;
public class DistributedServer {
private static final String CONNECT_STRING = "192.168.106.80:2181,192.168.106.81:2181,192.168.106.82:2181";
private static final int SESSION_TIME_OUT = 2000;
private static final String PARENT_NODE = "/servers";
private ZooKeeper zk = null;
CountDownLatch countDownLatch = new CountDownLatch(1);
/**
* 创建到zk的客户端连接
*
* @throws Exception
*/
public void getConnect() throws Exception {
zk = new ZooKeeper(CONNECT_STRING, SESSION_TIME_OUT, new Watcher() {
@Override
public void process(WatchedEvent event) {
if(event.getState()==KeeperState.SyncConnected){
countDownLatch.countDown();
}
}
});
countDownLatch.await();
}
/**
* 向zk集群注册服务器信息
*
* @param hostname
* @throws Exception
*/
public void registerServer(String hostname) throws Exception {
Stat exists = zk.exists(PARENT_NODE, false);
if(exists==null) zk.create(PARENT_NODE, null, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
String path = zk.create(PARENT_NODE + "/server", hostname.getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println(hostname + "is online.." + path);
}
/**
* 业务功能
*
* @throws InterruptedException
*/
public void handleBussiness(String hostname) throws InterruptedException {
System.out.println(hostname + "start working.....");
Thread.sleep(Long.MAX_VALUE);
}
public static void main(String[] args) throws Exception {
DistributedServer server = new DistributedServer();
// 获取zk连接
server.getConnect();
// 利用zk连接注册服务器信息(主机名)
server.registerServer(args[0]);
// 启动业务功能
server.handleBussiness(args[0]);
}
}
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