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20 package org.apache.hadoop.hbase.mapreduce;
21
22 import java.io.DataInput;
23 import java.io.DataOutput;
24 import java.io.IOException;
25 import java.util.ArrayList;
26 import java.util.List;
27
28 import org.apache.hadoop.conf.Configuration;
29 import org.apache.hadoop.io.NullWritable;
30 import org.apache.hadoop.io.Writable;
31 import org.apache.hadoop.mapreduce.InputFormat;
32 import org.apache.hadoop.mapreduce.InputSplit;
33 import org.apache.hadoop.mapreduce.JobContext;
34 import org.apache.hadoop.mapreduce.RecordReader;
35 import org.apache.hadoop.mapreduce.TaskAttemptContext;
36
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41
42
43 public class NMapInputFormat extends InputFormat<NullWritable, NullWritable> {
44 private static final String NMAPS_KEY = "nmapinputformat.num.maps";
45
46 @Override
47 public RecordReader<NullWritable, NullWritable> createRecordReader(
48 InputSplit split,
49 TaskAttemptContext tac) throws IOException, InterruptedException {
50 return new SingleRecordReader<NullWritable, NullWritable>(
51 NullWritable.get(), NullWritable.get());
52 }
53
54 @Override
55 public List<InputSplit> getSplits(JobContext context) throws IOException,
56 InterruptedException {
57 int count = getNumMapTasks(context.getConfiguration());
58 List<InputSplit> splits = new ArrayList<InputSplit>(count);
59 for (int i = 0; i < count; i++) {
60 splits.add(new NullInputSplit());
61 }
62 return splits;
63 }
64
65 public static void setNumMapTasks(Configuration conf, int numTasks) {
66 conf.setInt(NMAPS_KEY, numTasks);
67 }
68
69 public static int getNumMapTasks(Configuration conf) {
70 return conf.getInt(NMAPS_KEY, 1);
71 }
72
73 private static class NullInputSplit extends InputSplit implements Writable {
74 @Override
75 public long getLength() throws IOException, InterruptedException {
76 return 0;
77 }
78
79 @Override
80 public String[] getLocations() throws IOException, InterruptedException {
81 return new String[] {};
82 }
83
84 @Override
85 public void readFields(DataInput in) throws IOException {
86 }
87
88 @Override
89 public void write(DataOutput out) throws IOException {
90 }
91 }
92
93 private static class SingleRecordReader<K, V>
94 extends RecordReader<K, V> {
95
96 private final K key;
97 private final V value;
98 boolean providedKey = false;
99
100 SingleRecordReader(K key, V value) {
101 this.key = key;
102 this.value = value;
103 }
104
105 @Override
106 public void close() {
107 }
108
109 @Override
110 public K getCurrentKey() {
111 return key;
112 }
113
114 @Override
115 public V getCurrentValue(){
116 return value;
117 }
118
119 @Override
120 public float getProgress() {
121 return 0;
122 }
123
124 @Override
125 public void initialize(InputSplit split, TaskAttemptContext tac) {
126 }
127
128 @Override
129 public boolean nextKeyValue() {
130 if (providedKey) return false;
131 providedKey = true;
132 return true;
133 }
134
135 }
136 }