一、问题描述

对输入的多个文件进行合并，并剔除其中重复的内容，去重后的内容输出到一个文件中。

file1.txt中的内容:

20150101     x20150102     y20150103     x20150104     y

file2.txt中的内容:

20150105     z20150106     x20150101     y20150102     y

file3.txt中的内容:

20150103     x20150104     z20150105     y

二、MapReduce程序

编写MapReduce程序，运行环境参考我的上一篇博客

package com.javacore.hadoop;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;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 java.io.IOException;/** * Created by bee on 17/3/25. */public class FileMerge {
         public static class Map extends Mapper
     
       {
             private static Text text = new Text();        public void map(Object key, Text value, Context content) throws IOException, InterruptedException {            text = value;            content.write(text, new Text(""));        }    }    public static class Reduce extends Reducer
      
        {
             public void reduce(Text key, Iterable
       
         values, Context context) throws IOException, InterruptedException {            context.write(key, new Text(""));        }    }    public static void main(String[] args) throws Exception {        // delete output directory        FileUtil.deleteDir("output");        Configuration conf = new Configuration();        conf.set("fs.defaultFS", "hdfs://localhost:9000");        String[] otherArgs = new String[]{
    "input/filemerge/f*.txt",                "output"};        if (otherArgs.length != 2) {            System.err.println("Usage:Merge and duplicate removal 
         
         
          ");            System.exit(2);        }        Job job = Job.getInstance();        job.setJarByClass(FileMerge.class);        job.setMapperClass(Map.class);        job.setReducerClass(Reduce.class);        job.setOutputKeyClass(Text.class);        job.setOutputValueClass(Text.class);        FileInputFormat.addInputPath(job, new Path(otherArgs[0]));        FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));        System.exit(job.waitForCompletion(true) ? 0 : 1);    }}
         
        
       
      
     

三、输出

20150101     x20150101     y20150102     y20150103     x20150104     y20150104     z20150105     y20150105     z20150106     x