job/src/main/java/com/kylinolap/job/hadoop/invertedindex/RandomKeyDistributionReducer.java

/*
 * Copyright 2013-2014 eBay Software Foundation
 *
 * Licensed 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 com.kylinolap.job.hadoop.invertedindex;

import com.kylinolap.job.constant.BatchConstants;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.util.ReflectionUtils;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 * @author ysong1
 */
public class RandomKeyDistributionReducer<KEY extends Writable> extends
        Reducer<KEY, NullWritable, KEY, NullWritable> {

    private Configuration conf;
    private int regionNumber;
    private List<KEY> allSplits;

    @Override
    protected void setup(Context context) throws IOException {
        conf = context.getConfiguration();
        allSplits = new ArrayList<KEY>();
        regionNumber = Integer.parseInt(context.getConfiguration().get(BatchConstants.REGION_NUMBER));
    }

    @SuppressWarnings("unchecked")
    @Override
    public void reduce(KEY key, Iterable<NullWritable> values, Context context) throws IOException,
            InterruptedException {
        KEY keyCopy = (KEY) ReflectionUtils.newInstance(key.getClass(), conf);
        ReflectionUtils.copy(conf, key, keyCopy);
        allSplits.add(keyCopy);
    }

    @Override
    protected void cleanup(Context context) throws IOException, InterruptedException {
        int stepLength = allSplits.size() / regionNumber;
        for (int i = stepLength; i < allSplits.size(); i += stepLength) {
            context.write(allSplits.get(i), NullWritable.get());
        }
    }
}