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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  import org.apache.hadoop.classification.InterfaceStability;
23  
24  
25  /**
26   * Base class for internal listeners of ZooKeeper events.
27   *
28   * The {@link ZooKeeperWatcher} for a process will execute the appropriate
29   * methods of implementations of this class.  In order to receive events from
30   * the watcher, every listener must register itself via {@link ZooKeeperWatcher#registerListener}.
31   *
32   * Subclasses need only override those methods in which they are interested.
33   *
34   * Note that the watcher will be blocked when invoking methods in listeners so
35   * they must not be long-running.
36   */
37  @InterfaceAudience.Private
38  public abstract class ZooKeeperListener {
39  
40    // Reference to the zk watcher which also contains configuration and constants
41    protected ZooKeeperWatcher watcher;
42  
43    /**
44     * Construct a ZooKeeper event listener.
45     */
46    public ZooKeeperListener(ZooKeeperWatcher watcher) {
47      this.watcher = watcher;
48    }
49  
50    /**
51     * Called when a new node has been created.
52     * @param path full path of the new node
53     */
54    public void nodeCreated(String path) {
55      // no-op
56    }
57  
58    /**
59     * Called when a node has been deleted
60     * @param path full path of the deleted node
61     */
62    public void nodeDeleted(String path) {
63      // no-op
64    }
65  
66    /**
67     * Called when an existing node has changed data.
68     * @param path full path of the updated node
69     */
70    public void nodeDataChanged(String path) {
71      // no-op
72    }
73  
74    /**
75     * Called when an existing node has a child node added or removed.
76     * @param path full path of the node whose children have changed
77     */
78    public void nodeChildrenChanged(String path) {
79      // no-op
80    }
81  }