View Javadoc

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.Public
38  @InterfaceStability.Evolving
39  public abstract class ZooKeeperListener {
40  
41    // Reference to the zk watcher which also contains configuration and constants
42    protected ZooKeeperWatcher watcher;
43  
44    /**
45     * Construct a ZooKeeper event listener.
46     */
47    public ZooKeeperListener(ZooKeeperWatcher watcher) {
48      this.watcher = watcher;
49    }
50  
51    /**
52     * Called when a new node has been created.
53     * @param path full path of the new node
54     */
55    public void nodeCreated(String path) {
56      // no-op
57    }
58  
59    /**
60     * Called when a node has been deleted
61     * @param path full path of the deleted node
62     */
63    public void nodeDeleted(String path) {
64      // no-op
65    }
66  
67    /**
68     * Called when an existing node has changed data.
69     * @param path full path of the updated node
70     */
71    public void nodeDataChanged(String path) {
72      // no-op
73    }
74  
75    /**
76     * Called when an existing node has a child node added or removed.
77     * @param path full path of the node whose children have changed
78     */
79    public void nodeChildrenChanged(String path) {
80      // no-op
81    }
82  }