Hadoop排序

数据排序是许多实际任务在执行时要完成的第一项工作，比如学生成绩评比、数据建立索引等。
本次实例和数据去重类似，都是先对原始数据进行初步处理，为进一步的数据操作打好基础。

实例描述：
对输入文件中的数据进行排序。输入文件中的每行内容均为一个数字，即一个数据。要求在输出中每行有两个间隔的数字，其中，第二个数字代表原始数据，第一个数字代表这个原始数据在原始数据集中的位次。


样例输入：

[img]http://dl2.iteye.com/upload/attachment/0107/3090/09d04a70-813b-3bfc-8ba8-71b0de149671.png[/img]

样例输出：

[img]http://dl2.iteye.com/upload/attachment/0107/3092/07f505a3-c677-307e-b2a4-bbe5e80f4686.png[/img]

程序代码

package com.songjy.hadoop.demo;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
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 org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

public class Sort {

	public static class MyMapper extends
			Mapper<Object, Text, IntWritable, IntWritable> {

		@Override
		protected void map(Object key, Text value, Context context)
				throws IOException, InterruptedException {

			String line = value.toString();
			IntWritable data = new IntWritable(Integer.parseInt(line));

			context.write(data, new IntWritable(1));
		}

	}

	public static class MyReducer extends
			Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {

		private static IntWritable linenum = new IntWritable(1);

		@Override
		protected void reduce(IntWritable key, Iterable<IntWritable> values,
				Context context) throws IOException, InterruptedException {

			for (IntWritable v : values) {
				context.write(linenum, key);
				linenum = new IntWritable(linenum.get() + 1);
			}

			// linenum = new IntWritable(linenum.get() + 1);//代码放在这输出结果是啥样呢？o(∩_∩)o 哈哈

		}

	}

	public static void main(String[] args) throws IOException,
			ClassNotFoundException, InterruptedException {
		Configuration conf = new Configuration();

		String[] otherArgs = new GenericOptionsParser(conf, args)
				.getRemainingArgs();

		if (otherArgs.length != 2) {
			System.out.println("Usage: wordcount <in> <out>");
			System.exit(2);
		}

		Job job = new Job(conf, Sort.class.getName());
		job.setJarByClass(Sort.class);
		job.setMapperClass(MyMapper.class);
		job.setReducerClass(MyReducer.class);
		//job.setPartitionerClass(MyPartitioner.class);
		job.setOutputKeyClass(IntWritable.class);
		job.setOutputValueClass(IntWritable.class);

		FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
		FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));

		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}

}

以上引自书籍《Hadoop实战》第2版的第五章，不过我去掉了自定义Partition部分代码，从结果来看，输出结果仍是正确(参看上面已有截图)，是否仍需要自定义Partition的必要,望大牛们指点！ :D

Partition部分代码

	/**
	 * 自定义Partitioner函数，此函数根据输入数据的最大值和MapReduce框架中
	 * Partitioner的数量获取将输入数据按照大小分块的边界，然后根据输入数值和
	 * 边界的关系返回对应的Partitioner ID
	 */
	public static class MyPartitioner extends
			Partitioner<IntWritable, IntWritable> {

		@Override
		public int getPartition(IntWritable key, IntWritable value,
				int numPartitions) {

			System.out.println("numPartitions=" + numPartitions);

			int maxnum = 652232;

			int bound = maxnum / numPartitions + 1;

			System.out.println("bound=" + bound);

			int keynum = key.get();

			for (int i = 0; i < numPartitions; i++) {
				if ((keynum < (bound * i)) && (keynum >= (bound * (i - 1))))
					//return i - 1;
					return (i - 1) >= 0 ? (i - 1) : 0;//partition是从0开始的，默认的返回应该给个0
			}

			//return -1;
			return 0;//partition是从0开始的，默认的返回应该给个0

		}

	}

下面的错误信息是因为[color=blue]partition是从0开始的，默认的返回应该给个0[/color]

[color=red]15/04/06 15:32:40 INFO mapred.JobClient: map 0% reduce 0%
15/04/06 15:36:54 INFO mapred.JobClient: Task Id : attempt_201503291109_0008_m_000002_0, Status : FAILED
java.io.IOException: Illegal partition for 26 (-1)
at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:1078)
at org.apache.hadoop.mapred.MapTask$NewOutputCollector.write(MapTask.java:690)
at org.apache.hadoop.mapreduce.TaskInputOutputContext.write(TaskInputOutputContext.java:80)
at com.songjy.hadoop.demo.Sort$MyMapper.map(Sort.java:29)
at com.songjy.hadoop.demo.Sort$MyMapper.map(Sort.java:1)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:145)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:764)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:364)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1190)
at org.apache.hadoop.mapred.Child.main(Child.java:249)

attempt_201503291109_0008_m_000002_0: numPartitions=1
attempt_201503291109_0008_m_000002_0: bound=652233
15/04/06 15:38:11 INFO mapred.JobClient: Task Id : attempt_201503291109_0008_m_000001_0, Status : FAILED
attempt_201503291109_0008_m_000001_0: numPartitions=1
attempt_201503291109_0008_m_000001_0: bound=652233
15/04/06 15:38:24 INFO mapred.JobClient: Task Id : attempt_201503291109_0008_m_000000_0, Status : FAILED
java.io.IOException: Illegal partition for 2 (-1)
at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:1078)
at org.apache.hadoop.mapred.MapTask$NewOutputCollector.write(MapTask.java:690)
at org.apache.hadoop.mapreduce.TaskInputOutputContext.write(TaskInputOutputContext.java:80)
at com.songjy.hadoop.demo.Sort$MyMapper.map(Sort.java:29)
at com.songjy.hadoop.demo.Sort$MyMapper.map(Sort.java:1)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:145)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:764)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:364)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:422)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1190)
at org.apache.hadoop.mapred.Child.main(Child.java:249)

attempt_201503291109_0008_m_000000_0: numPartitions=1
attempt_201503291109_0008_m_000000_0: bound=652233
15/04/06 15:38:24 INFO mapred.JobClient: Task Id : attempt_201503291109_0008_m_000001_1, Status : FAILED
java.io.IOException: Illegal partition for 5956 (-1)
at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:1078)[/color]