zookeeper的API简单编程二---服务器上下线的实时通知处理

当客户服务器端是一个集群时，集群内服务器的数量可能随时发生变化，有的服务器down机下线，有的服务器上线工作提供服务，而客户端如何感知服务的上下线，并入服务器进行通信呢，这个问题就可以通过zookeeper进行解决。

问题分析：

1.每次有服务器上线提供服务时就要在zookeeper上创建一个临时序列节点，这样当服务器下线时，该服务程序结束，就会删除这个节点

2.上下线都会触发父节点NodeChildrenChanged事件通知

3.客户端注册监听器监听父节点，当接收到这个事件通知时，就去访问父节点，并获取父节点下创建了哪些子节点，就表示可以与哪些服务器进行通信，再通过一定的策略决定于那一台服务器进行交互

server的代码

package bigdata.zkserertest;

import java.io.IOException;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;

public class zkServers {
	
	
	private static final String connectString = "lanc05:2181,lanc06:2181,lanc07:2181";
	private static final int sessionTimeout =2000;
	private static final String parent="/servers";
	static ZooKeeper zk =null;
	
	public static void testparent() throws Exception{
		//判断是否存在这个父目录
		Stat exists = zk.exists(parent, false);
		//如果不存在则创建
		if(exists == null){
			zk.create(parent, "IIIII".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);	
			System.out.println(" not exit ,then create----");
		}		
	}
	
	public static void getconnect() throws Exception {
		zk =new ZooKeeper(connectString, sessionTimeout, new Watcher() {
			@Override
			public void process(WatchedEvent event) {
				// TODO Auto-generated method stub
				System.out.print(event + "++++++" + event.getPath());
				try {
					zk.getChildren(parent, true);
				} catch (Exception e) {				
				}
			}
		});
	}
	
	public static void registserver(String args) throws Exception{
		//在父目录下创建一个临时的序列化子节点
		String createsever = zk.create(parent+"/server", args.getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
		System.out.println(args + " is online " + createsever );
	}
	
	public static void serverwork(String args) throws Exception {
		System.out.println(args + " start working .....");
		Thread.sleep(Long.MAX_VALUE);
		
	}
	
	public static void main(String[] args) throws Exception {
		
		//// 获取zookeeper的链接
		 getconnect();
		 //先判断着个父目录是否存在，不存在就创建
		 testparent();
		//在zookeeper上注册该服务器
		 registserver(args[0]);
		//执行这个服务器的相关业务
		 serverwork(args[0]);

		
		
	}

}

client代码：

package bigdata.zkserertest;

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 zkClientss {
	
	private static final String connectString = "lanc05:2181,lanc06:2181,lanc07:2181";
	private static final int sessionTimeout =2000;
	private static final String parent="/servers";
	static ZooKeeper zk =null;
	private static volatile List<String> serverList;
	
	public  void getconnect() throws Exception {
		zk =new ZooKeeper(connectString, sessionTimeout, new Watcher() {
			@Override
			public void process(WatchedEvent event) {
				try {
					//再次注册监听，并更新信息
					getznode();
				} catch (Exception e) {				
				}
			}
		});
	}
	
/**
 * 获取子节点的相关信息和数据
 * @throws Exception
 */
public  void getznode() throws Exception{
	List<String> servers = new ArrayList<String>();
	//获取子节点信息，并对父节点进行监听
		List<String> children = zk.getChildren(parent, true); //使用true 就是使用上面的监听器
		for(String child:children){
			System.out.println(child);
			byte[] data = zk.getData(parent+"/"+child, false, null);
			//c把获取的数据给成员变量，以方便给各个客户端的业务使用
			servers.add(new String(data));	
		}
		serverList =servers;
		System.out.println(serverList);
	}

/**
 * 客户端业务
 * @throws Exception
 */
public  void clientwork() throws Exception {
	System.out.println("client starts working .....");
	Thread.sleep(Long.MAX_VALUE);
	
}
	
	public static void main(String[] args) throws Exception {
		
		// 获取zookeeper的链接
		zkClientss zc= new zkClientss();
		zc.getconnect();
		//查看zookeeper下/servers目录下的子目录
		zc.getznode();
		//业务线程使用
		zc.clientwork();
	}

}