自定义分组Group

package com.ccse.hadoop.group;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.RawComparator;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableComparator;
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 com.ccse.hadoop.sort.SortApp;

/**
 * 自定义分组，当第一列相同时，获取第二列的最大值
 * @author woshiccna
 *
 */
public class GroupApp {

  public static final String INPUT_PATH = "hdfs://chaoren1:9000/sortinput";
  public static final String OUTPUT_PATH = "hdfs://chaoren1:9000/sortoutput";
  
  public static void main(String[] args) throws IOException, 
       URISyntaxException, ClassNotFoundException, InterruptedException {

    Configuration conf = new Configuration();
    FileSystem fileSystem = FileSystem.get(new URI(OUTPUT_PATH), conf);
    fileSystem.delete(new Path(OUTPUT_PATH), true);
    
    Job job = new Job(conf, SortApp.class.getSimpleName());
    job.setJarByClass(SortApp.class);
    
    FileInputFormat.setInputPaths(job, new Path(INPUT_PATH));
    
    job.setMapperClass(MyMapper.class);
    job.setMapOutputKeyClass(MyK2.class);
    job.setMapOutputValueClass(LongWritable.class);
    
    job.setGroupingComparatorClass(MyGroupComparator.class);
    
    job.setReducerClass(MyReducer.class);
    job.setOutputKeyClass(LongWritable.class);
    job.setOutputValueClass(LongWritable.class);
    
    FileOutputFormat.setOutputPath(job, new Path(OUTPUT_PATH));
    
    job.waitForCompletion(true);
    
  }
  
  public static class MyMapper extends Mapper<LongWritable, Text, MyK2, LongWritable> {

    @Override
    protected void map(LongWritable key, Text value,
        Mapper<LongWritable, Text, MyK2, LongWritable>.Context context)
        throws IOException, InterruptedException {
      if (value != null) {
        String[] splitted = value.toString().split("\t");
        LongWritable second = new LongWritable(Long.parseLong(splitted[1]));
        context.write(new MyK2(Long.parseLong(splitted[0]), Long.parseLong(splitted[1])), second);
      }
    }
    
  }
  
  public static class MyReducer extends Reducer<MyK2, LongWritable, LongWritable, LongWritable> {
    @Override
    protected void reduce(
        MyK2 key,
        Iterable<LongWritable> values,
        Reducer<MyK2, LongWritable, LongWritable, LongWritable>.Context context)
        throws IOException, InterruptedException {
      long max = Long.MIN_VALUE;
      for (LongWritable writable : values) {  //找出第二列的最大值
        if (writable.get() > max) {
          max = writable.get();
        }
      }
      context.write(new LongWritable(key.first), new LongWritable(max));
    }
  }
  
  public static class MyK2 implements WritableComparable<MyK2> {

    private long first;
    private long second;
    
    public MyK2() {}
    
    public MyK2(long first, long second) {
      this.first = first;
      this.second = second;
    }
    
    @Override
    public void write(DataOutput out) throws IOException {
      out.writeLong(this.first);
      out.writeLong(this.second);
    }

    @Override
    public void readFields(DataInput in) throws IOException {
      this.first = in.readLong();
      this.second = in.readLong();
    }

    @Override
    public int compareTo(MyK2 to) {
      if (to != null) {
        long dis = this.first - to.first;
        if (dis != 0) {  //首先根据first进行排序
          return (int)dis;
        } else {   //然后根据second进行排序
          return (int)(this.second - to.second);
        }
      }
      return 0;
    }
  }
  
  public static class MyGroupComparator implements RawComparator<MyK2> {

    @Override
    public int compare(MyK2 arg0, MyK2 arg1) {
      return 0;
    }

    /**
     * b1  表示第1个参与比较的字节数组
     * s1  表示第1个字节数组中开始比较的位置
     * l1  表示第1个字节数组参与比较的字节长度
     * b2  表示第2个参与比较的字节数组
     * s2  表示第2个字节数组中开始比较的位置
     * l2  表示第2个字节数组参与比较的字节长度
     */
    @Override
    public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) {
      return WritableComparator.compareBytes(b1, s1, 8, b2, s2, 8);
    }
    
  }
  
}