mapreduce中最简单的wordcount程序

1.首先建一个WCMapper 类：

package com.zhichao.wan.mr.wordcount1;

import java.io.IOException;

import org.apache.commons.lang.StringUtils;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class WCMapper extends Mapper{

    @Override
    protected void map(LongWritable key, Text value,Context context)
            throws IOException, InterruptedException {
        //1.获取每一行的字符串
        String sting = value.toString();

        //2.开始切割字符串，成为一个个的单词
        String[] words = StringUtils.split(sting, " ");

        for (String word : words) {

            context.write(new Text(word), new LongWritable(1));
        }

    }

}

2.然后建一个WCReducer 类：

package com.zhichao.wan.mr.wordcount1;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class WCReducer extends Reducer{

    @Override
    protected void reduce(Text key, Iterable values,Context context)
            throws IOException, InterruptedException {

        long count=0;

        for (LongWritable value : values) {

            count+=value.get();
        }

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



    }

}

3.最后

package com.zhichao.wan.mr.wordcount1;

import java.io.IOException;

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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class WCRunner {

    /**
     * @param args
     * @throws Exception 
     */
    public static void main(String[] args) throws Exception {

        Job job=Job.getInstance();

        job.setJarByClass(WCRunner.class);

        job.setMapperClass(WCMapper.class);
        job.setReducerClass(WCReducer.class);

        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongWritable.class);

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

        FileInputFormat.setInputPaths(job, new Path("/wc/srcdata/"));

        FileOutputFormat.setOutputPath(job, new Path("/wc/output"));

        job.waitForCompletion(true);

    }

}

5.将程序打成jar包，并拷贝到linux中。

6.建一个测试文件

7.运行jar包，指定主程序的地址

8.运行结果：