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 java.io.IOException;
22
23 import org.apache.commons.logging.Log;
24 import org.apache.commons.logging.LogFactory;
25 import org.apache.hadoop.hbase.classification.InterfaceAudience;
26 import org.apache.hadoop.hbase.classification.InterfaceStability;
27 import org.apache.hadoop.hbase.client.Mutation;
28 import org.apache.hadoop.io.Writable;
29
30 /**
31 * Convenience class that simply writes all values (which must be
32 * {@link org.apache.hadoop.hbase.client.Put} or
33 * {@link org.apache.hadoop.hbase.client.Delete} instances)
34 * passed to it out to the configured HBase table. This works in combination
35 * with {@link TableOutputFormat} which actually does the writing to HBase.<p>
36 *
37 * Keys are passed along but ignored in TableOutputFormat. However, they can
38 * be used to control how your values will be divided up amongst the specified
39 * number of reducers. <p>
40 *
41 * You can also use the {@link TableMapReduceUtil} class to set up the two
42 * classes in one step:
43 * <blockquote><code>
44 * TableMapReduceUtil.initTableReducerJob("table", IdentityTableReducer.class, job);
45 * </code></blockquote>
46 * This will also set the proper {@link TableOutputFormat} which is given the
47 * <code>table</code> parameter. The
48 * {@link org.apache.hadoop.hbase.client.Put} or
49 * {@link org.apache.hadoop.hbase.client.Delete} define the
50 * row and columns implicitly.
51 */
52 @InterfaceAudience.Public
53 @InterfaceStability.Stable
54 public class IdentityTableReducer
55 extends TableReducer<Writable, Mutation, Writable> {
56
57 @SuppressWarnings("unused")
58 private static final Log LOG = LogFactory.getLog(IdentityTableReducer.class);
59
60 /**
61 * Writes each given record, consisting of the row key and the given values,
62 * to the configured {@link org.apache.hadoop.mapreduce.OutputFormat}.
63 * It is emitting the row key and each
64 * {@link org.apache.hadoop.hbase.client.Put Put} or
65 * {@link org.apache.hadoop.hbase.client.Delete} as separate pairs.
66 *
67 * @param key The current row key.
68 * @param values The {@link org.apache.hadoop.hbase.client.Put Put} or
69 * {@link org.apache.hadoop.hbase.client.Delete} list for the given
70 * row.
71 * @param context The context of the reduce.
72 * @throws IOException When writing the record fails.
73 * @throws InterruptedException When the job gets interrupted.
74 */
75 @Override
76 public void reduce(Writable key, Iterable<Mutation> values, Context context)
77 throws IOException, InterruptedException {
78 for(Mutation putOrDelete : values) {
79 context.write(key, putOrDelete);
80 }
81 }
82 }