MapReduce编程(二) 文件合并和去重

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     x
20150102     y
20150103     x
20150104     y

file2.txt中的内容:

20150105     z
20150106     x
20150101     y
20150102     y

file3.txt中的内容:

20150103     x
20150104     z
20150105     y

二、MapReduce程序

编写MapReduce程序，运行环境参考我的上一篇博客Intellij Idea配置MapReduce编程环境

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<Object, Text, Text, Text> {
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<Text, Text, Text, Text> {
        public void reduce(Text key, Iterable<Text> 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 <in> <out>");
            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     x
20150101     y
20150102     y
20150103     x
20150104     y
20150104     z
20150105     y
20150105     z
20150106     x