1 /**
2 *
3 * Licensed to the Apache Software Foundation (ASF) under one
4 * or more contributor license agreements. See the NOTICE file
5 * distributed with this work for additional information
6 * regarding copyright ownership. The ASF licenses this file
7 * to you under the Apache License, Version 2.0 (the
8 * "License"); you may not use this file except in compliance
9 * with the License. You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 */
19 package org.apache.hadoop.hbase.zookeeper;
20
21 import org.apache.hadoop.hbase.classification.InterfaceAudience;
22
23 /**
24 * Base class for internal listeners of ZooKeeper events.
25 *
26 * The {@link ZooKeeperWatcher} for a process will execute the appropriate
27 * methods of implementations of this class. In order to receive events from
28 * the watcher, every listener must register itself via {@link ZooKeeperWatcher#registerListener}.
29 *
30 * Subclasses need only override those methods in which they are interested.
31 *
32 * Note that the watcher will be blocked when invoking methods in listeners so
33 * they must not be long-running.
34 */
35 @InterfaceAudience.Private
36 public abstract class ZooKeeperListener {
37
38 // Reference to the zk watcher which also contains configuration and constants
39 protected ZooKeeperWatcher watcher;
40
41 /**
42 * Construct a ZooKeeper event listener.
43 */
44 public ZooKeeperListener(ZooKeeperWatcher watcher) {
45 this.watcher = watcher;
46 }
47
48 /**
49 * Called when a new node has been created.
50 * @param path full path of the new node
51 */
52 public void nodeCreated(String path) {
53 // no-op
54 }
55
56 /**
57 * Called when a node has been deleted
58 * @param path full path of the deleted node
59 */
60 public void nodeDeleted(String path) {
61 // no-op
62 }
63
64 /**
65 * Called when an existing node has changed data.
66 * @param path full path of the updated node
67 */
68 public void nodeDataChanged(String path) {
69 // no-op
70 }
71
72 /**
73 * Called when an existing node has a child node added or removed.
74 * @param path full path of the node whose children have changed
75 */
76 public void nodeChildrenChanged(String path) {
77 // no-op
78 }
79
80 /**
81 * @return The watcher associated with this listener
82 */
83 public ZooKeeperWatcher getWatcher() {
84 return this.watcher;
85 }
86 }