com.cloudera.sa.hbase.to.hdfs.utils.NMapInputFormat.java Source code

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Here is the source code for com.cloudera.sa.hbase.to.hdfs.utils.NMapInputFormat.java

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package com.cloudera.sa.hbase.to.hdfs.utils;

/**
*
* 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.
*/

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;
        }

    }
}