1、Zookeeper 应用案例(上下线动态感知)
8.1 案例1——服务器上下线动态感知
8.1.1 需求描述
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
8.1.2 设计思路
8.1.3 代码开发
1、客户端实现
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(); } } |
2、服务器端实现
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]); } } |
