wordcount

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最基本的，需要手动写出。

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package com.qr.mr.wordcount;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import java.io.IOException;
import java.util.StringTokenizer;

/**
 * StringTokenizer
 * https://www.cnblogs.com/gnivor/p/4509268.html
 *
 *
 * http://hadoop.apache.org/docs/r1.0.4/cn/mapred_tutorial.html#Map%2FReduce+-+%E7%94%A8%E6%88%B7%E7%95%8C%E9%9D%A2
 * http://hadoop.apache.org/docs/stable/hadoop-mapreduce-client/hadoop-mapreduce-client-core/MapReduceTutorial.html#Payload
 *
 */

public class WordCount {

    public static class TokenizerMapper extends Mapper<Object, Text,Text, IntWritable>{
        private final static IntWritable one = new IntWritable(1);
        private Text word = new Text();
        public void map(Object key,Text value,Context context) throws IOException, InterruptedException {

            StringTokenizer itr = new StringTokenizer(value.toString());//StringTokenizer
            while (itr.hasMoreTokens()){
                word.set(itr.nextToken());
                context.write(word,one);
            }
        }
    }

    public static class IntSumReducer extends Reducer<Text,IntWritable,Text,IntWritable>{
        private IntWritable result = new IntWritable();
        public void reduce(Text 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);
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf,"word count");
        job.setJarByClass(WordCount.class);

        job.setMapperClass(TokenizerMapper.class);
        job.setCombinerClass(IntSumReducer.class);
        job.setReducerClass(IntSumReducer.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        FileInputFormat.addInputPath(job,new Path("/Users/lifei/Desktop/ab/a.txt"));
        FileOutputFormat.setOutputPath(job,new Path("/Users/lifei/Desktop/ab_out"));
        System.exit(job.waitForCompletion(true)? 0 : 1);
    }
}