環境

	hadoop-2.9.1
	windows7
	idea15

示例資料

file1.txt和file2.txt檔案儲存在路徑：C:\bigdata\example_data\mr_example\exp_02\

file1.txt

2012-3-1 a
2012-3-2 b
2012-3-3 c
2012-3-4 d
2012-3-5 a
2012-3-6 b
2012-3-7 c
2012-3-3 c

file2.txt

2012-3-1 b
2012-3-2 a
2012-3-3 b
2012-3-4 d
2012-3-5 a
2012-3-6 c
2012-3-7 d
2012-3-3 c

程式碼部分

DeMapper.java

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

import java.io.IOException;

/**
 * 去重操作
 */
public class DeMapper extends Mapper<LongWritable, Text, Text, NullWritable> {
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        context.write(new Text(value.toString().trim()), NullWritable.get());
    }
}
 

DeReducer.java

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

import java.io.IOException;

public class DeReducer extends Reducer<Text, NullWritable, Text, NullWritable> {
    public void reduce(Text key, Iterable<NullWritable> values, Context context) throws IOException, InterruptedException {
        context.write(key, NullWritable.get());
    }
}
 

JobMain.java

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.NullWritable;
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;
import org.apache.hadoop.mapreduce.protocol.ClientProtocol;

import java.io.IOException;

public class JobMain {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);
        job.setJarByClass(JobMain.class);

        job.setMapperClass(DeMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(NullWritable.class);

        job.setReducerClass(DeReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(NullWritable.class);

        FileInputFormat.addInputPath(job, new Path(args[0]));

        Path path = new Path(args[1]);
        FileSystem fs = FileSystem.get(conf);
        if(fs.exists(path)) {
            fs.delete(path, true);
        }
        FileOutputFormat.setOutputPath(job, path);
        job.setNumReduceTasks(1);
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}

執行程式碼

在windows7環境下執行前需要設定HADOOP_CLASSPATH
set HADOOP_CLASSPATH=mr_example.jar
注：mr_example.jar是以上程式碼打成jar包的名稱

執行命令
hadoop jar的全類名(包名+類名) 資料路徑 輸出路徑

eg:
C:\hadoop-2.9.1\bin\hadoop jar的全類名（包名+類名） file:///C:…\mr_example\exp_02*.txt C:…\mr_example\exp_02\out\

執行結果

2012-3-1 a
2012-3-1 b
2012-3-2 a
2012-3-2 b
2012-3-3 b
2012-3-3 c
2012-3-4 d
2012-3-5 a
2012-3-6 b
2012-3-6 c
2012-3-7 c
2012-3-7 d