Hadoop 二次排序，

Hadoop 二次排序，

对value进行排序。
    实现过程：
    1.ComboKey(WritableComparable)
        对比方法。

package com.mao.hdfs.secondSort;

import org.apache.hadoop.io.WritableComparable;

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

/**
 * 自定义组合key
 */
public class ComboKey implements WritableComparable<ComboKey> {
    private int year ;
    private int temp ;

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public int getTemp() {
        return temp;
    }

    public void setTemp(int temp) {
        this.temp = temp;
    }

    /**
     * 对key进行比较实现
     */
    public int compareTo(ComboKey o) {
        int y0 = o.getYear();
        int t0 = o.getTemp() ;
        //年份相同(升序)
        if(year == y0){
            //气温降序
            return -(temp - t0) ;
        }
        else{
            return year - y0 ;
        }
    }

    /**
     * 串行化过程
     */
    public void write(DataOutput out) throws IOException {
        //年份
        out.writeInt(year);
        //气温
        out.writeInt(temp);
    }

    public void readFields(DataInput in) throws IOException {
        year = in.readInt();
        temp = in.readInt();
    }
}

    2.定义分区类
        

package com.mao.hdfs.secondSort;

import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.Partitioner;

/**
 * 自定义分区类
 */
public class YearPartitioner extends Partitioner<ComboKey,NullWritable> {

    public int getPartition(ComboKey key, NullWritable nullWritable, int numPartitions) {
        int year = key.getYear();
        return year % numPartitions;
    }
}

    3.自定义排序对比器
        

package com.mao.hdfs.secondSort;

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

/**
 *ComboKeyComparator 自定义排序对比器
 */
public class ComboKeyComparator extends WritableComparator {

    protected ComboKeyComparator() {
        super(ComboKey.class, true);
    }

    public int compare(WritableComparable a, WritableComparable b) {
        ComboKey k1 = (ComboKey) a;
        ComboKey k2 = (ComboKey) b;
        return k1.compareTo(k2);
    }
}

    4.自定义分组对比器

package com.mao.hdfs.secondSort;

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

/**
 * 按照年份进行分组对比器实现
 */
public class YearGroupComparator extends WritableComparator {

    protected YearGroupComparator() {
        super(ComboKey.class, true);
    }

    public int compare(WritableComparable a, WritableComparable b) {
        ComboKey k1 = (ComboKey)a ;
        ComboKey k2 = (ComboKey)b ;
        return k1.getYear() - k2.getYear() ;
    }
}

mapper类：

package com.mao.hdfs.secondSort;

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

import java.io.IOException;

/**
 * Mapper
 */
public class MaxTempMapper extends Mapper<LongWritable, Text, ComboKey, NullWritable>{

    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String line = value.toString();
        String[] arr = line.split(" ");

        ComboKey keyOut = new ComboKey();
        keyOut.setYear(Integer.parseInt(arr[0]));
        keyOut.setTemp(Integer.parseInt(arr[1]));
        context.write(keyOut,NullWritable.get());
    }
}

Reduce类：

package com.mao.hdfs.secondSort;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.Reducer;

import java.io.IOException;

/**
 * Reducer
 */
public class MaxTempReducer extends Reducer<ComboKey, NullWritable, IntWritable, IntWritable>{

    /**
     */
    protected void reduce(ComboKey key, Iterable<NullWritable> values, Context context) throws IOException, InterruptedException {
        int year = key.getYear();
        int temp = key.getTemp();
        System.out.println("==============>reduce");
        for(NullWritable v : values){
            System.out.println(key.getYear() + " : " + key.getTemp());
        }
        context.write(new IntWritable(year),new IntWritable(temp));
    }
}

APP类：

package com.mao.hdfs.secondSort;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

/**
 *
 */
public class MaxTempApp {
    public static void main(String[] args) throws Exception {

        Configuration conf = new Configuration();
        conf.set("fs.defaultFS","file:///");

        Job job = Job.getInstance(conf);

        //设置job的各种属性
        job.setJobName("SecondarySortApp");                        //作业名称
        job.setJarByClass(MaxTempApp.class);                 //搜索类
        job.setInputFormatClass(TextInputFormat.class); //设置输入格式

        //添加输入路径
        FileInputFormat.addInputPath(job,new Path(args[0]));
        //设置输出路径
        FileOutputFormat.setOutputPath(job,new Path(args[1]));

        job.setMapperClass(MaxTempMapper.class);             //mapper类
        job.setReducerClass(MaxTempReducer.class);           //reducer类

        //设置Map输出类型
        job.setMapOutputKeyClass(ComboKey.class);            //
        job.setMapOutputValueClass(NullWritable.class);      //

        //设置ReduceOutput类型
        job.setOutputKeyClass(IntWritable.class);
        job.setOutputValueClass(IntWritable.class);         //

        //设置分区类
        job.setPartitionerClass(YearPartitioner.class);
        //设置分组对比器
        job.setGroupingComparatorClass(YearGroupComparator.class);
        //设置排序对比器
        job.setSortComparatorClass(ComboKeyComparator.class);

        job.setNumReduceTasks(3);                           //reduce个数
        //
        job.waitForCompletion(true);
    }
}