我的项目是显示最高，最低和平均温度。我已经完成了，但是我必须使用groupby键来显示这个函数。在我的应用程序中有4个单选按钮，分别代表年份、月份、日期和城市。如果我选择一个，那么它会要求我输入聚合函数（max，min，avg）。为了这些我需要改变我的想法 CompositeGroupKey 同学们，但我对此一无所知。所以请帮助我，并提供有关的变化需要做的代码输入。
司机：

import org.apache.hadoop.io.*;
import org.apache.hadoop.fs.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class MaxTemperature
{             
            public static void Main (String[] args) throws Exception
            {
                        if (args.length != 2)
                        {
                               System.err.println("Please Enter the input and output parameters");
                               System.exit(-1);
                        }

                      Job job = new Job();
                      job.setJarByClass(MaxTemperature.class);
                      job.setJobName("Max temperature");

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

                      job.setMapperClass(MaxTemperatureMapper.class);
                      job.setReducerClass(MaxTemperatureReducer.class);

                      job.setMapOutputKeyClass(CompositeGroupKey.class);
                      job.setMapOutputValueClass(IntWritable.class);

                      job.setOutputKeyClass(CompositeGroupKey.class);
                      job.setOutputValueClass(DoubleWritable.class);

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

Map器：

import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
import java.io.IOException;

public class MaxTemperatureMapper extends Mapper <LongWritable, Text, CompositeGroupKey, IntWritable>
{
public void map(LongWritable key, Text value, Context context) throws IOException,  InterruptedException
     {
    String line = value.toString();
    int year = Integer.parseInt(line.substring(0,4));
    String mnth = line.substring(7,10);
    int date = Integer.parseInt(line.substring(10,12));
    int temp= Integer.parseInt(line.substring(12,14));

    CompositeGroupKey cntry = new CompositeGroupKey(year,mnth, date);

    context.write(cntry, new IntWritable(temp));
            }
}

减速器：

import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapreduce.*;
import java.io.IOException;

public class MaxTemperatureReducer extends Reducer <CompositeGroupKey, IntWritable, CompositeGroupKey, CompositeGroupkeyall >{

    public void reduce(CompositeGroupKey key, Iterable<IntWritable> values , Context context) throws IOException,InterruptedException
            {

            Double max = Double.MIN_VALUE;
            Double min =Double.MAX_VALUE;

            for (IntWritable value : values  ) 
            {               
                min = Math.min(min, value.get());
                max = Math.max(max, value.get());

            }

            CompositeGroupkeyall val =new CompositeGroupkeyall(max,min);
            context.write(key, val);
            }
}

以及复合键：

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableUtils;

class CompositeGroupKey implements WritableComparable<CompositeGroupKey> {
    int year;
    String mnth;
    int date;
    CompositeGroupKey(int y, String c, int d){
        year = y;
        mnth = c;
        date = d;
    }
    CompositeGroupKey(){}

    public void write(DataOutput out) throws IOException {
        out.writeInt(year);
        WritableUtils.writeString(out, mnth);
        out.writeInt(date);
        }
    public void readFields(DataInput in) throws IOException {
        this.year = in.readInt();
        this.mnth = WritableUtils.readString(in);
        this.date = in.readInt();
        }
    public int compareTo(CompositeGroupKey pop) {
        if (pop == null)
            return 0;
        int intcnt;
        intcnt = Integer.valueOf(year).toString().compareTo(Integer.valueOf(pop.year).toString());
        if(intcnt != 0){
            return intcnt;
        }else if(mnth.compareTo(pop.mnth) != 0){
            return mnth.compareTo(pop.mnth);
        }else{
            return Integer.valueOf(date).toString().compareTo(Integer.valueOf(pop.date).toString());
        }
    }
    public String toString() {
        return year + " :" + mnth.toString() + " :" + date;
        }   
}

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.io.WritableComparable;
class CompositeGroupkeyall implements WritableComparable<CompositeGroupkeyall> {
    Double max;
    Double min;

    CompositeGroupkeyall(double x, double y){
        max = x ;
        min = y ;
    }
    CompositeGroupkeyall(){}

    public void readFields(DataInput in) throws IOException {
        this.max = in.readDouble();
        this.min = in.readDouble();
    }

    public void write(DataOutput out) throws IOException {
        out.writeDouble(max);

        out.writeDouble(min);

        }

    public int compareTo(CompositeGroupkeyall arg0) {
        return -1;
    }

    public String toString() {
        return max + "   " + min +"   " ;
        }
}