mr统计每年中每月温度的前三名

weatherMapper

package com.laoxiao.mr.weather;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class WeatherMapper extends Mapper<Text, Text, MyKey, DoubleWritable>{

    SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    protected void map(Text key, Text value, Context context)
            throws java.io.IOException ,InterruptedException {
        try {
            Date d = df.parse(key.toString());
            Calendar c=Calendar.getInstance();
            c.setTime(d);
            int year=c.get(Calendar.YEAR);
            int month=c.get(Calendar.MONTH);
            double hot =Double.parseDouble(value.toString().substring(0, value.toString().lastIndexOf("c")));
            context.write(new MyKey(year,month+1,hot), new DoubleWritable(hot));
        } catch (Exception e) {
            e.printStackTrace();
        }

    };

}

weatherReducer

 package com.laoxiao.mr.weather;

 import org.apache.hadoop.io.DoubleWritable;
 import org.apache.hadoop.io.NullWritable;
 import org.apache.hadoop.io.Text;
 import org.apache.hadoop.mapreduce.Reducer;

 public class WeatherReducer extends Reducer<MyKey, DoubleWritable, Text, NullWritable>{
     protected void reduce(MyKey arg0, java.lang.Iterable<DoubleWritable> arg1, Context arg2)
             throws java.io.IOException ,InterruptedException {
         int i=0;
         for(DoubleWritable d:arg1){
             i++;
             arg2.write(new Text(arg0.getYear()+"\t"+arg0.getMonth()+"\t"+d.get()),NullWritable.get());
             if(i==3){
                 break;
             }
         }
     };

 }

MyKey

package com.laoxiao.mr.weather;

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

import org.apache.hadoop.io.WritableComparable;

public class MyKey implements WritableComparable<MyKey>{

    private int year;
    private int month;
    private double hot;
    public MyKey(int year, int month, double hot) {
        super();
        this.year = year;
        this.month = month;
        this.hot = hot;
    }
    public MyKey() {
        // TODO Auto-generated constructor stub
    }
    public int getYear() {
        return year;
    }
    public void setYear(int year) {
        this.year = year;
    }
    public int getMonth() {
        return month;
    }
    public void setMonth(int month) {
        this.month = month;
    }
    public double getHot() {
        return hot;
    }
    public void setHot(double hot) {
        this.hot = hot;
    }

    public void readFields(DataInput arg0) throws IOException {
        this.year=arg0.readInt();
        this.month=arg0.readInt();
        this.hot=arg0.readDouble();
    }
    public void write(DataOutput arg0) throws IOException {
        arg0.writeInt(year);
        arg0.writeInt(month);
        arg0.writeDouble(hot);
    }

    //判断对象是否是同一个对象，当该对象作为输出的key
    public int compareTo(MyKey o) {
        int r1 =Integer.compare(this.year, o.getYear());
        if(r1==0){
            int r2 =Integer.compare(this.month, o.getMonth());
            if(r2==0){
                return  Double.compare(this.hot, o.getHot());
            }else{
                return r2;
            }
        }else{
            return r1;
        }
    }

}

MyPartitioner

package com.laoxiao.mr.weather;

import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.mapreduce.lib.partition.HashPartitioner;

public class MyPartitioner extends HashPartitioner<MyKey, DoubleWritable>{

    //执行时间越短越好
    public int getPartition(MyKey key, DoubleWritable value, int numReduceTasks) {
        return (key.getYear()-1949)%numReduceTasks;
    }

}

MySort

package com.laoxiao.mr.weather;

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

public class MySort extends WritableComparator{

    public MySort() {
        super(MyKey.class,true);
    }

    public int compare(WritableComparable a, WritableComparable b) {
        MyKey k1=(MyKey)a;
        MyKey k2=(MyKey)b;
        int r1=Integer.compare(k1.getYear(), k2.getYear());
        if(r1==0){
            int r2=Integer.compare(k1.getMonth(), k2.getMonth());
            if(r2==0){
                return -Double.compare(k1.getHot(),k2.getHot());
            }else{
                return r2;
            }
        }else{
            return r1;
        }

    }
}

MyGroup

package com.laoxiao.mr.weather;

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

public class MyGroup extends WritableComparator{

    public MyGroup(){
        super(MyKey.class,true);
    }

    public int compare(WritableComparable a, WritableComparable b) {
        MyKey k1 =(MyKey) a;
        MyKey k2 =(MyKey) b;
        int r1 =Integer.compare(k1.getYear(), k2.getYear());
        if(r1==0){
            return Integer.compare(k1.getMonth(), k2.getMonth());
        }else{
            return r1;
        }

    }
}

设置了三个reducer进程，最后的结果就放到了三个文件中。