Zookeeper:JavaAPI watcher机制

1.watcher架构

watcher由三个部分组成：

zookeeper服务端、zookeeper客户端、客户端的ZKWatchManager对象。

 

接口设计：

Watcher接口中含有一个内部接口Event,其中含有两个枚举KeeperStat(通知状态)和EventType(事件类型)

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public enum KeeperState {             /** Unused, this state is never generated by the server */             @Deprecated             Unknown (-1),               /** The client is in the disconnected state - it is not connected              * to any server in the ensemble. */             Disconnected (0),               /** Unused, this state is never generated by the server */             @Deprecated             NoSyncConnected (1),               /** The client is in the connected state - it is connected              * to a server in the ensemble (one of the servers specified              * in the host connection parameter during ZooKeeper client              * creation). */             SyncConnected (3),               /**              * Auth failed state              */             AuthFailed (4),               /**              * The client is connected to a read-only server, that is the              * server which is not currently connected to the majority.              * The only operations allowed after receiving this state is              * read operations.              * This state is generated for read-only clients only since              * read/write clients aren't allowed to connect to r/o servers.              */             ConnectedReadOnly (5),               /**               * SaslAuthenticated: used to notify clients that they are SASL-authenticated,               * so that they can perform Zookeeper actions with their SASL-authorized permissions.               */             SaslAuthenticated(6),               /** The serving cluster has expired this session. The ZooKeeper              * client connection (the session) is no longer valid. You must              * create a new client connection (instantiate a new ZooKeeper              * instance) if you with to access the ensemble. */             Expired (-112);               private final int intValue;     // Integer representation of value                                             // for sending over wire               KeeperState(int intValue) {                 this.intValue = intValue;             }               public int getIntValue() {                 return intValue;             }               public static KeeperState fromInt(int intValue) {                 switch(intValue) {                     case   -1: return KeeperState.Unknown;                     case    0: return KeeperState.Disconnected;                     case    1: return KeeperState.NoSyncConnected;                     case    3: return KeeperState.SyncConnected;                     case    4: return KeeperState.AuthFailed;                     case    5: return KeeperState.ConnectedReadOnly;                     case    6: return KeeperState.SaslAuthenticated;                     case -112: return KeeperState.Expired;                       default:                         throw new RuntimeException("Invalid integer value for conversion to KeeperState");                 }             }         }

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public enum EventType {             None (-1),             NodeCreated (1),             NodeDeleted (2),             NodeDataChanged (3),             NodeChildrenChanged (4);               private final int intValue;     // Integer representation of value                                             // for sending over wire               EventType(int intValue) {                 this.intValue = intValue;             }               public int getIntValue() {                 return intValue;             }               public static EventType fromInt(int intValue) {                 switch(intValue) {                     case -1: return EventType.None;                     case  1: return EventType.NodeCreated;                     case  2: return EventType.NodeDeleted;                     case  3: return EventType.NodeDataChanged;                     case  4: return EventType.NodeChildrenChanged;                       default:                         throw new RuntimeException("Invalid integer value for conversion to EventType");                 }             }                   }

　　

 

 

 以node节点为例，说明调用的注册方法和可监听时间间的关系：

注册方式	Created	ChildrenChanged	Changed	Deleted
zk.exists("/node",watcher)	可监控		可监控	可监控
zk.getData("/node",watcher)			可监控	可监控
zk.getChildren("/node",watcher)		可监控		可监控

 

 

 

 

 

 2.注册Watcher

KeeperState 通知状态

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public class ZKWatcher implements Watcher{       static CountDownLatch latch = new CountDownLatch(1);       static ZooKeeper zooKeeper;       public static void main(String[] args) throws Exception{         Watcher watcher;         zooKeeper = new ZooKeeper("192.168.10.132:2181", 5000, new ZKWatcher());         latch.await();     }       public void process(WatchedEvent event) {         if(event.getType() == Event.EventType.None){             if(event.getState() == Event.KeeperState.SyncConnected){                 System.out.println("连接成功");                 latch.countDown();             }else if(event.getState() == Event.KeeperState.Disconnected){                 System.out.println("断开连接");             }else if(event.getState() == Event.KeeperState.Expired){                 System.out.println("会话超时");             }else if(event.getState() == Event.KeeperState.AuthFailed){                 System.out.println("认证失败");             }         }       } }

3.检查节点是否存在

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//使用链接对象的监视器 exists(String path,boolean b) //自定义监视器 exists(String path,Watacher watcher) //NodeCreated:节点创建 //NodeDeleted:节点删除 //NodeDataChanged:节点内容发生变化

4.查看节点

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//使用连接对象的监视器 getData(String path,boolean b,Stat stat) //自定义监视器 getData(String path,Watcher w,Stat stat)   //NodeDeleted:节点删除 //NodeDataChanged:节点内容变化

5.查看子节点　

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//使用连接对象的监视器 getChildren(String path,boolean b) //自定义监视器 getChildren(String path,Watcher w)   //NodeDeleted:节点删除 //NodeChildrenChanged:子节点内容变化