初探ZooKeeper之Watcher

一、Watcher的使用

package ygsoft.gris.zookeeper;
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import java.util.concurrent.CountDownLatch;

/**
 * 事件实现原理;
 */
public class WatcherDemo {
    public static void main(String[] args) {
        try {
            CountDownLatch countDownLatch = new CountDownLatch(1);
            ZooKeeper zooKeeper = new ZooKeeper("192.168.80.33:2181,192.168.80.36:2181,192.168.80.39:2181",
                    4000, new Watcher() {
                @Override
                public void process(WatchedEvent watchedEvent) {
                    System.out.println("全局监听器：" + watchedEvent.getPath() + "->" + watchedEvent.getType());
                    if (Event.KeeperState.SyncConnected == watchedEvent.getState()) {
                        countDownLatch.countDown();
                    }
                }
            });
            countDownLatch.await();
            System.out.println(zooKeeper.getState());

            //定义路径
            final String path = "/zookeeper-persis-thomas";
            //创建节点
            zooKeeper.create(path, "0".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            Stat stat = zooKeeper.exists(path, new Watcher() {
                @Override
                public void process(WatchedEvent watchedEvent) {
                    System.out.println("自定义监听器：" + watchedEvent.getPath() + "->" + watchedEvent.getType());
                    try {
                        //第二参数传入为true是，表示默认执行全局的监听器
                        zooKeeper.exists(path, true);
                    } catch (KeeperException e) {
                        e.printStackTrace();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            });

            //修改操作时触发监听器
            stat = zooKeeper.setData(path, "1".getBytes(), stat.getVersion());

            //删除时触发监听器
            zooKeeper.delete(path, stat.getVersion());
            zooKeeper.close();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
//代码演示：

二、事件触发

//特性：当数据发生变更时，zookeeper会产生一个watch事件，并且会发送到客户端。但是客户端只会接收到一次通知。
//如果后续这个节点再次发生变更，那么之前设置watch的客户端不会再接收到消息，可以通过循环监听从而达到永久监听的效果
//===如何注册事件机制
//getData Exsits getChildren 来绑定事件
//===如何触发事件
//凡是事务类型操作都会触发，如create/setData/delete