MapReduce 1.x 编程 系列三 Reduce阶段实现

Reduce代码就是做加和统计，

package org.freebird.reducer;

import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapreduce.Reducer.Context;
import org.apache.hadoop.mapreduce.Reducer;

public class LogReducer<Key> extends Reducer<Key, IntWritable, Key,IntWritable> {
    private IntWritable result = new IntWritable();

    public void reduce(Key key, Iterable<IntWritable> values,
                       Context context) throws IOException, InterruptedException {
        int sum = 0;
        for (IntWritable val : values) {
            sum += val.get();
        }
        result.set(sum);
        context.write(key, result);
    }
}

迭代遍历values，取出所有的value，都是1, 简单加和。

然后结果写入到context中。 注意，这里的context是Reducer包的Context。