hadoop 学习自定义排序

（网易云课程hadoop大数据实战学习笔记）

自定义排序，是基于k2的排序，设现有以下一组数据，分别表示矩形的长和宽，先按照面积的升序进行排序。

1. 99
2. 66
3. 78
4. 11
5. 54

现在需要重新定义数据类型，MR的key值必须继承WritableComparable接口，因此定义RectangleWritable数据类型如下：

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.io.WritableComparable;
public class RectangleWritable implements WritableComparable {
	int length,width;

	public RectangleWritable() {
		super();
		// TODO Auto-generated constructor stub
	}
	public RectangleWritable(int length, int width) {
		super();
		this.length = length;
		this.width = width;
	}

	public int getLength() {
		return length;
	}
	public void setLength(int length) {
		this.length = length;
	}
	public int getWidth() {
		return width;
	}
	public void setWidth(int width) {
		this.width = width;
	}
	@Override
	public void write(DataOutput out) throws IOException {
		// TODO Auto-generated method stub
		out.writeInt(length);
		out.writeInt(width);
	}
	@Override
	public void readFields(DataInput in) throws IOException {
		// TODO Auto-generated method stub
		this.length=in.readInt();
		this.width=in.readInt();
	}
	@Override
	public int compareTo(Object arg0) {
		// TODO Auto-generated method stub
		RectangleWritable other = (RectangleWritable)arg0;
		if (this.getLength() * this.getWidth() > other.length * other.width ) {
			 return 1;
		}
		if (this.getLength() * this.getWidth() < other.length * other.width ) {
			return -1;
		}
		return 0;
	}
	@Override
	public String toString() {
		return   this.getLength() + "\t" + this.getWidth();
	}

}

其中，compareTo方法自定义排序规则，然后由框架进行排序。

map函数和Reduce函数并无大变化，还是按照WrodCount的思路进行，具体代码如下：

import java.io.IOException;
import java.net.URI;
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.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.Reducer;
public class SelfDefineSort {
	/**
	 * @param args
	 * @author nwpulisz
	 * @date 2016.4.1
	 */
	static final String INPUT_PATH="hdfs://192.168.255.132:9000/input";
	static final String OUTPUT_PATH="hdfs://192.168.255.132:9000/output";

	public static void main(String[] args) throws Exception {
		// TODO Auto-generated method stub
		Configuration conf = new Configuration();
		Path outPut_path= new Path(OUTPUT_PATH);
		Job job = new Job(conf, "SelfDefineSort");

		//如果输出路径是存在的，则提前删除输出路径
		FileSystem fileSystem = FileSystem.get(new URI(OUTPUT_PATH), conf);
		if(fileSystem.exists(outPut_path))
		{
			fileSystem.delete(outPut_path,true);
		}
		job.setJarByClass(RectangleWritable.class);
		FileInputFormat.setInputPaths(job, INPUT_PATH);
		FileOutputFormat.setOutputPath(job, outPut_path);

		job.setMapperClass(MyMapper.class);
		job.setReducerClass(MyReducer.class);

		job.setMapOutputKeyClass(RectangleWritable.class);
		job.setMapOutputValueClass(NullWritable.class);

		job.setOutputKeyClass(IntWritable.class);
		job.setOutputValueClass(IntWritable.class);
		job.waitForCompletion(true);
	}

	static class MyMapper extends Mapper<LongWritable, Text, RectangleWritable, NullWritable>{
		protected void map(LongWritable k1, Text v1,
                Context context) throws IOException, InterruptedException {
			String[] splits = v1.toString().split("\t");
			RectangleWritable k2 = new RectangleWritable(Integer.parseInt(splits[0]),
					Integer.parseInt(splits[1]));

			context.write(k2,NullWritable.get());
		}
	}

	static class MyReducer extends Reducer<RectangleWritable, NullWritable,
					IntWritable, IntWritable>{
		protected void reduce(RectangleWritable k2,
				Iterable<NullWritable> v2s,
				Context context)
				throws IOException, InterruptedException {
			// TODO Auto-generated method stub
			context.write(new IntWritable(k2.getLength()), new IntWritable(k2.getWidth()));
		}

	}
}

根据自定义结果，输出结果如下：

来自为知笔记(Wiz)