zookeeper中如何实现事件监听Watcher
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Watcher是zookeeper的事件监听机制,今天我们来看看Watcher类的代码都包含了什么内容?
Watcher
Watcher是一个接口,定义了process方法,需要子类实现。其代表了实现Watcher接口时必须实现的的方法,即定义进行处理,WatchedEvent表示观察的事件。
abstract public void process(WatchedEvent event);
内部类
1、Event接口
表示事件代表的状态,其包含了KeeperState和EventType两个内部枚举类。
KeeperState
KeeperState是一个枚举类,其定义了在事件发生时Zookeeper所处的各种状态,其还定义了一个从整型值返回对应状态的方法fromInt。
@InterfaceAudience.Public public interface Event { /** * Enumeration of states the ZooKeeper may be at the event */ @InterfaceAudience.Public public enum KeeperState { /** Unused, this state is never generated by the server */ //未知状态,服务器不再产生此状态 @Deprecated Unknown (-1), /** The client is in the disconnected state - it is not connected * to any server in the ensemble. */ //断开 Disconnected (0), /** Unused, this state is never generated by the server */ //未同步连接,不再使用,服务器不会产生此状态 @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). */ //同步连接状态 SyncConnected (3), /** * Auth failed state */ //认证失败状态 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. */ //只读连接状态 ConnectedReadOnly (5), /** * SaslAuthenticated: used to notify clients that they are SASL-authenticated, * so that they can perform Zookeeper actions with their SASL-authorized permissions. */ //SASL认证通过状态 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 The ZooKeeper * client connection (the session) is no longer valid.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. */ //过期状态 Expired (-112), /** * The client has been closed. This state is never generated by * the server, but is generated locally when a client calls * {@link ZooKeeper#close()} or {@link ZooKeeper#close(int)} */ //关闭 Closed (7); //代表状态的整型值 private final int intValue; // Integer representation of value // for sending over wire KeeperState(int intValue) { this.intValue = intValue; } public int getIntValue() { return intValue; } //从整型构造相应的状态 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; case 7: return KeeperState.Closed; default: throw new RuntimeException("Invalid integer value for conversion to KeeperState"); } } }
EventType
EventType是一个枚举类,其定义了事件的类型(如创建节点、删除节点等事件),同时,其还定义了一个从整型值返回对应事件类型的方法fromInt。
@InterfaceAudience.Public public enum EventType { //无 None (-1), //结点创建 NodeCreated (1), //结点删除 NodeDeleted (2), //结点数据变化 NodeDataChanged (3), //子结点变化 NodeChildrenChanged (4), //监听移除 DataWatchRemoved (5), //子结点监听移除 ChildWatchRemoved (6); private final int intValue; // Integer representation of value // for sending over wire EventType(int intValue) { this.intValue = intValue; } public int getIntValue() { return intValue; } //从整型构造相应的事件 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; case 5: return EventType.DataWatchRemoved; case 6: return EventType.ChildWatchRemoved; default: throw new RuntimeException("Invalid integer value for conversion to EventType"); } } }
2、枚举类WatcherType
监听器类型枚举
@InterfaceAudience.Public public enum WatcherType { //子监听器 Children(1), //数据监听 Data(2), //任意 Any(3); // Integer representation of value private final int intValue; private WatcherType(int intValue) { this.intValue = intValue; } public int getIntValue() { return intValue; } //整数到类型的转换 public static WatcherType fromInt(int intValue) { switch (intValue) { case 1: return WatcherType.Children; case 2: return WatcherType.Data; case 3: return WatcherType.Any; default: throw new RuntimeException( "Invalid integer value for conversion to WatcherType"); } } }
WatchedEvent
/** * Create a WatchedEvent with specified type, state and path */ public WatchedEvent(EventType eventType, KeeperState keeperState, String path) { this.keeperState = keeperState; this.eventType = eventType; this.path = path; }
WatchedEvent类包含了三个属性,分别代表事件发生时Zookeeper的状态、事件类型和发生事件所涉及的节点路径。
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