zookeeper中如何实现事件监听Watcher

小编给大家分享一下zookeeper中如何实现事件监听Watcher，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！

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 The ZooKeeper             * client connection (the session) is no longer valid.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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