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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.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  }