Hadoop 案例2----数据去重问题

1、原始数据
1）file1：

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 

2）file2：

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 

2.mapper：

package cn.edu.bjut.del;

import java.io.IOException;

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

public class DelMapper extends Mapper<LongWritable, Text, Text, IntWritable> {

    @Override
    protected void map(LongWritable key, Text value, Context context)
            throws IOException, InterruptedException {
        String line = value.toString().trim();
        if(!"".equals(line)) {
            context.write(new Text(line), new IntWritable(1));
        }
    }
}

3.Reducer：

package cn.edu.bjut.del;

import java.io.IOException;

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

public class DelReducer extends Reducer {

    @Override
    protected void reduce(Text key, Iterable value, Context context)
            throws IOException, InterruptedException {
        context.write(key, NullWritable.get());
    }

}

4.主程序：

package cn.edu.bjut.del;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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;


public class MainJob {
    public static void main(String[] args) throws Exception {

        Configuration conf = new Configuration();
        Job job = new Job(conf, "del");
        job.setJarByClass(MainJob.class);

        job.setMapperClass(DelMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);

        job.setReducerClass(DelReducer.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.waitForCompletion(true);
    }
}