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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.mapreduce;
20  
21  import org.apache.hadoop.classification.InterfaceAudience;
22  import org.apache.hadoop.classification.InterfaceStability;
23  import org.apache.hadoop.hbase.client.Mutation;
24  import org.apache.hadoop.mapreduce.Reducer;
25  
26  /**
27   * Extends the basic <code>Reducer</code> class to add the required key and
28   * value input/output classes. While the input key and value as well as the
29   * output key can be anything handed in from the previous map phase the output
30   * value <u>must</u> be either a {@link org.apache.hadoop.hbase.client.Put Put}
31   * or a {@link org.apache.hadoop.hbase.client.Delete Delete} instance when
32   * using the {@link TableOutputFormat} class.
33   * <p>
34   * This class is extended by {@link IdentityTableReducer} but can also be
35   * subclassed to implement similar features or any custom code needed. It has
36   * the advantage to enforce the output value to a specific basic type.
37   *
38   * @param <KEYIN>  The type of the input key.
39   * @param <VALUEIN>  The type of the input value.
40   * @param <KEYOUT>  The type of the output key.
41   * @see org.apache.hadoop.mapreduce.Reducer
42   */
43  @InterfaceAudience.Public
44  @InterfaceStability.Stable
45  public abstract class TableReducer<KEYIN, VALUEIN, KEYOUT>
46  extends Reducer<KEYIN, VALUEIN, KEYOUT, Mutation> {
47  }