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 }