参考资料

参考这个做一次性的监听
https://blog.csdn.net/sunnylinner/article/details/52013616

参考这个做永久监听，需要一个专门的zk的server，复制监听和回调，然后不同的client去操作zk，然后被server监听并处理
https://www.jianshu.com/p/9968356828b6

监听相关

事件的类型：

• EventType.None (zkClient连接服务器连接成功的时候，事件类型为None)
• EventType.NodeCreated
• EventType.NodeDeleted
• EventType.NodeDataChanged
• EventType.NodeChildrenChanged

Zookeeper通知机制

客户端注册监听它关心的目录节点，当目录节点发生变化（数据改变、被删除、子目录节点增加删除）时，zookeeper会通知客户端。

常见的设置监听

1. 通过zk.exists(path, true);来设置一次性的zk的watch的监听，该方法不能用于PERSISTENT_SEQUENTIAL，因为路径不确定
2. 通过zk.exists(path,Watcher)来对该path设置专门的Watcher，该方法不能用于PERSISTENT_SEQUENTIAL，因为路径不确定
3. 通过zk.getChildren(PARENT, true);来对当前节点的所有子节点设置一次性的监听，可以用于PERSISTENT_SEQUENTIAL

   private static final String PARENT = "/name"; //在zk初始化的时候设置一个全局的Watcher，实现等待初始化的功能 ZooKeeper zk = new ZooKeeper("127.0.0.1:2181",3000, new Watcher() { public void process(WatchedEvent event) { System.out.println("已经触发了" + event.getType() + "事件！"); if ( Event.KeeperState.SyncConnected == event.getState()&&event.getType()==EventType.None) { connectedSemaphore.countDown(); } } }); connectedSemaphore.await(); zk.exists(PARENT+"/rootTest", true); zk.create(PARENT+"/rootTest", "mydata".getBytes(), Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT); zk.exists(PARENT+"/rootTest", true); zk.delete(PARENT+"/rootTest", -1); //或者 zk.getChildren(PARENT, true); zk.create(PARENT+"/root", "mydata".getBytes(), Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT_SEQUENTIAL);

永久性监听的服务端和客户端的实现

Server端，持续监听母目录下面的节点变化，并且做出相应的相应

public class ZooKeeperServer {
    private static final String PARENT = "/name";
    public static void main(String[] args) throws Exception {
    	MyWatcher watch=new MyWatcher();
        ZooKeeper zk = new ZooKeeper("127.0.0.1:2181",3000,watch);
        watch.setZk(zk);
        Thread.sleep(Long.MAX_VALUE);
    }
}
//如果根节点为空就创建，不为空就不处理
public class MyWatcher implements Watcher{
	private ZooKeeper zk=null;
	private static final String PARENT = "/name";
	public void setZk(ZooKeeper zk) {
		this.zk = zk;
	}
	 public void process(WatchedEvent event) {
		 String path = event.getPath();
         EventType type = event.getType();
         System.out.println("路径"+path+"已经触发了" +type + "事件！");
         try {
			if(zk.exists(PARENT,true)==null){
				zk.create(PARENT, "root".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT);
			}
			zk.getChildren(PARENT, true);
		} catch (Exception e) {
		} 
     }
}

客户端，单次触发

public class ZooKeeperClient {
	private static final String PARENT = "/name";
    public static void main(String[] args) throws Exception {
        ZooKeeper zk = new ZooKeeper("127.0.0.1:2181",3000,null);
        zk.create(PARENT+"/testRootPath", "testRootData".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT_SEQUENTIAL);
        zk.close();
    }
}