Hadoop之MapReduce—Wordcount

一、問題描述

     場景：有大量文件，裏面存儲了單詞
     任務：如何統計每個單詞出現的次數？

二、數據格式

     2.1 輸入數據

      hello tom
      hello jerry
      hello kitty
      hello world
      hello tom

     2.2 輸出格式

      hello 5

      jerry 1  

      kitty 1  

      tom 2  

      world 1

三、分析

                          step1                                                                     step2                                                                            step3

     

四、代碼實現

       WorldCount代碼

package edu.jianwei.wc;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
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;

public class WorldCount {

	static class WCMapper extends
			Mapper<LongWritable, Text, Text, LongWritable> {

		@Override
		protected void map(LongWritable key, Text value,
				Mapper<LongWritable, Text, Text, LongWritable>.Context context)
				throws IOException, InterruptedException {
			String line = value.toString();
			String[] words = line.split(" ");
			for (String word : words) {
				context.write(new Text(word), new LongWritable(1));
			}

		}

	}

	static class WCReduce extends
			Reducer<Text, LongWritable, Text, LongWritable> {

		@Override
		protected void reduce(Text key, Iterable<LongWritable> v2s,
				Reducer<Text, LongWritable, Text, LongWritable>.Context context)
				throws IOException, InterruptedException {
			long count = 0;
			for (LongWritable v2 : v2s) {
				count += v2.get();

			}
			context.write(key, new LongWritable(count));
		}
	}

	public static void main(String[] args) throws Exception {
		Configuration conf = new Configuration();
		Job job = Job.getInstance(conf);

		job.setJarByClass(WorldCount.class);

		job.setMapperClass(WCMapper.class);
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(LongWritable.class);
		FileInputFormat.setInputPaths(job, new Path("/wc"));

		job.setReducerClass(WCReduce.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(LongWritable.class);
		FileOutputFormat.setOutputPath(job, new Path("/wc/wcout"));

		job.waitForCompletion(true);
	}
}