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1   /**
2    * Copyright 2007 The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *     http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  package org.apache.hadoop.hbase.mapreduce;
21  
22  import org.apache.hadoop.io.Writable;
23  import org.apache.hadoop.mapreduce.Reducer;
24  
25  /**
26   * Extends the basic <code>Reducer</code> class to add the required key and
27   * value input/output classes. While the input key and value as well as the
28   * output key can be anything handed in from the previous map phase the output
29   * value <u>must</u> be either a {@link org.apache.hadoop.hbase.client.Put Put}
30   * or a {@link org.apache.hadoop.hbase.client.Delete Delete} instance when
31   * using the {@link TableOutputFormat} class.
32   * <p>
33   * This class is extended by {@link IdentityTableReducer} but can also be
34   * subclassed to implement similar features or any custom code needed. It has
35   * the advantage to enforce the output value to a specific basic type.
36   *
37   * @param <KEYIN>  The type of the input key.
38   * @param <VALUEIN>  The type of the input value.
39   * @param <KEYOUT>  The type of the output key.
40   * @see org.apache.hadoop.mapreduce.Reducer
41   */
42  public abstract class TableReducer<KEYIN, VALUEIN, KEYOUT>
43  extends Reducer<KEYIN, VALUEIN, KEYOUT, Writable> {
44  }