/**
* Copyright 2010 The Apache Software Foundation
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hbase.mapreduce;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.InputFormat;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.JobContext;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
/**
* Input format that creates a configurable number of map tasks
* each provided with a single row of NullWritables. This can be
* useful when trying to write mappers which don't have any real
* input (eg when the mapper is simply producing random data as output)
*/
public class NMapInputFormat extends InputFormat<NullWritable, NullWritable> {
private static final String NMAPS_KEY = "nmapinputformat.num.maps";
@Override
public RecordReader<NullWritable, NullWritable> createRecordReader(
InputSplit split,
TaskAttemptContext tac) throws IOException, InterruptedException {
return new SingleRecordReader<NullWritable, NullWritable>(
NullWritable.get(), NullWritable.get());
}
@Override
public List<InputSplit> getSplits(JobContext context) throws IOException,
InterruptedException {
int count = getNumMapTasks(context.getConfiguration());
List<InputSplit> splits = new ArrayList<InputSplit>(count);
for (int i = 0; i < count; i++) {
splits.add(new NullInputSplit());
}
return splits;
}
public static void setNumMapTasks(Configuration conf, int numTasks) {
conf.setInt(NMAPS_KEY, numTasks);
}
public static int getNumMapTasks(Configuration conf) {
return conf.getInt(NMAPS_KEY, 1);
}
private static class NullInputSplit extends InputSplit implements Writable {
@Override
public long getLength() throws IOException, InterruptedException {
return 0;
}
@Override
public String[] getLocations() throws IOException, InterruptedException {
return new String[] {};
}
@Override
public void readFields(DataInput in) throws IOException {
}
@Override
public void write(DataOutput out) throws IOException {
}
}
private static class SingleRecordReader<K, V>
extends RecordReader<K, V> {
private final K key;
private final V value;
boolean providedKey = false;
SingleRecordReader(K key, V value) {
this.key = key;
this.value = value;
}
@Override
public void close() {
}
@Override
public K getCurrentKey() {
return key;
}
@Override
public V getCurrentValue(){
return value;
}
@Override
public float getProgress() {
return 0;
}
@Override
public void initialize(InputSplit split, TaskAttemptContext tac) {
}
@Override
public boolean nextKeyValue() {
if (providedKey) return false;
providedKey = true;
return true;
}
}
}