任务描述：

一组数据，按照年份的不同将其分别存放在不同的文件里

example Data：

2013 1
2013 5
2014 5
2014 8
2015 9
2015 4

Code：

package mrTest;

import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Partitioner;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class zidingyiPartition {

	public static class myPartition extends Partitioner<LongWritable, LongWritable>{

		public int getPartition(LongWritable key, LongWritable value, int numTaskReduces) {
			// TODO Auto-generated method stub
			if(key.get()==2013){
				return 0;
			}else if(key.get()==2014){
				return 1;
			}else{
				return 2;
			}
		}
		
	}
	
	public static class Map extends Mapper<Object, Text, LongWritable,LongWritable>{
		public void map(Object key, Text value, Context context) throws IOException, InterruptedException{
				String[] line = value.toString().split("\t");
				context.write( new LongWritable(Integer.parseInt(line[0])) ,  new LongWritable(Integer.parseInt(line[1])) );
		}
	}
	
	public static class Reduce extends Reducer<LongWritable, LongWritable, LongWritable, LongWritable>{
		public void reduce(LongWritable key, Iterable<LongWritable> values, Context context) throws IOException, InterruptedException{
			for (LongWritable longWritable : values) {
				context.write(key, longWritable);
			}
		}
	}
	
	public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
		// TODO Auto-generated method stub

		Job job = new Job();
		job.setJarByClass(zidingyiPartition.class);
		//  1
		FileInputFormat.addInputPath(job, new Path(args[0]));
		// 2
		job.setMapperClass(Map.class);
	    job.setMapOutputKeyClass(LongWritable.class);
	    job.setMapOutputValueClass(LongWritable.class);
	    //   3
	    job.setPartitionerClass(myPartition.class);
	    //  4
	    //  5
	    job.setNumReduceTasks(3);
	    //  6
	    job.setReducerClass(Reduce.class);
	    job.setOutputKeyClass(LongWritable.class);
	    job.setOutputValueClass(LongWritable.class);
	    //  7
	    FileOutputFormat.setOutputPath(job, new Path(args[1]));
	    //  8
	    System.exit(job.waitForCompletion(true)? 0 : 1);
	}

}

结果展示：