zookeeper应用 - 监控

package monitor;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;
/**
 * 监听客户端的上下线
 * @author lisg
 *
 */
public class ServerMonitor {
	public static final String HOSTS = "vm1";
	private ZooKeeper zk = null;
	
	public static final String PARENT_PATH = "/monitor";
	
	private static int client_count = 0;
	public ServerMonitor() {
		final CountDownLatch cdl = new CountDownLatch(1);
		try {
			zk = new ZooKeeper(HOSTS, 5000, new Watcher() {
				@Override
				public void process(WatchedEvent event) {
					if(KeeperState.SyncConnected.equals(event.getState())) {
						cdl.countDown();
					}
				}
			});
			
			cdl.await();
			
			//创建父节点
			if(zk.exists(PARENT_PATH, false) == null) {
				zk.create(PARENT_PATH, 
						"".getBytes(), 
						ZooDefs.Ids.OPEN_ACL_UNSAFE, 
						CreateMode.PERSISTENT);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public void run() {
		try {
			zk.getChildren(PARENT_PATH, new ClientChangeWatcher());
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	class ClientChangeWatcher implements Watcher {
		@Override
		public void process(WatchedEvent event) {
			try {
				if(Event.EventType.NodeChildrenChanged.equals(event.getType())) {
					//获取子节点，同时注册监听
					final List<String> children = zk.getChildren(PARENT_PATH, this);
					if(client_count > children.size()) {
						System.out.println("有客户端下线");
					} else {
						System.out.println("有客户端上线");
					}
					client_count = children.size();
				}
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}
	
	public static void main(String[] args) {
		new ServerMonitor().run();
		
		try {
			TimeUnit.DAYS.sleep(1);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}