1、需求描述：输入有3列，对3列值进行排序

inputFile:
ab d 1a
b1 d1 1a
c2 a1 1a
d3 e3 1a
d2 a4 1b
b1 a2 1b
c1 b2 1c

2、代码

import java.io.DataInput;
import java.io.DataOutput;
import java.io.CharArrayWriter;
import java.io.CharArrayReader;
import java.util.StringTokenizer;

import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.WritableComparable;

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;

public class TripleIntSortApp {
    public static void main(String[] args) throws Exception {
        // 创建Job对象
        Job job = Job.getInstance(new Configuration(), TripleIntSortApp.class.getSimpleName());
        // 设置运行job的类
        job.setJarByClass(TripleIntSortApp.class);
        // 设置输入的路径
        FileInputFormat.setInputPaths(job, args[0]);
        // 设置mapper类
        job.setMapperClass(TripleStringSortMapper.class);
        // 设置map输出的key value
        job.setMapOutputKeyClass(TripleString.class);
        job.setMapOutputValueClass(NullWritable.class);
        // 设置reduce类
        job.setReducerClass(TripleStringSortReducer.class);
        // 设置reduce输出的key value值
        job.setOutputKeyClass(TripleString.class);
        job.setOutputValueClass(NullWritable.class);
        // 设置输出的路径
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        // 提交job
        job.waitForCompletion(true);        
    }
    
    public static class TripleStringSortMapper extends Mapper<LongWritable, Text, TripleString, NullWritable>{
        TripleString k3 = new TripleString();
        @Override
        protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, TripleString, NullWritable>.Context context) throws IOException, InterruptedException {
            String[] splited = value.toString().split("\t");
            k3.set(splited[0], splited[1], splited[2]);
            context.write(k3, NullWritable.get());
            System.out.println("Mapper-----第一个数:"+k3.first+" 第二个数:"+k3.second+" 第三个数："+k3.third);
        }
    }
    
    public static class TripleStringSortReducer extends Reducer<TripleString, NullWritable, TripleString, NullWritable>{
        int i=1;
        @Override
        protected void reduce(TripleString k3, Iterable<NullWritable> arg1, Reducer<TripleString, NullWritable, TripleString, NullWritable>.Context context) throws IOException, InterruptedException {
            context.write(k3, NullWritable.get());
            System.out.println("调用次数"+(i++));
            System.out.println("Reducer-----第一个数:"+k3.first+" 第二个数:"+k3.second+" 第三个数："+k3.third);
        }
    }
    
    public static class TripleString implements WritableComparable<TripleString>{
        String first;
        String second;
        String third;
        public void write(DataOutput out) throws IOException {
            out.writeUTF(first);
            out.writeUTF(second);
            out.writeUTF(third);
        }
        
        public void set(String s1, String s2, String s3){
            this.first = s1;
            this.second = s2;
            this.third = s3;
        }

        public void readFields(DataInput in) throws IOException {
            this.first = in.readUTF();
            this.second = in.readUTF();
            this.third = in.readUTF();
        }

//          正序：从小到大排序
//        public int compareTo(TripleString o) {
//            //int r1 = this.first - o.first;
//            int r1 = (this.first).compareTo(o.first);
//            if(r1 < 0){
//                return -1;
//            }else if(r1 > 0){
//                return 1;
//            }
//            //int r2 = this.second - o.second;
//          int r2 = (this.second).compareTo(o.second);
//            if(r2 < 0){
//                return -1;
//            }else if(r2 > 0){
//                return 1;
//            }
//            //int r3 = this.third - o.third;
//          int r3 = (this.third).compareTo(o.third);
//            return (r3 < 0 ? -1 : (r3 > 0 ? 1: 0));
//        }
        
//        倒序：从大到小排序
        public int compareTo(TripleString o) {
//            int r1 = this.first - o.first;
            int r1 = (this.first).compareTo(o.first);
            if(r1 > 0){
                return -1;
            }else if(r1 < 0){
                return 1;
            }
//            int r2 = this.second - o.second;
            int r2 = (this.second).compareTo(o.second);
            if(r2 > 0){
                return -1;
            }else if(r2 < 0){
                return 1;
            }
//            int r3 = this.third - o.third;
            int r3 = (this.third).compareTo(o.third);
            return (r3 > 0 ? -1 : (r3 < 0 ? 1: 0));
        }
        
        @Override
        public String toString() {
            return this.first+"\t"+this.second+"\t"+this.third;
        }
    }
}

3、输出结果

d3 e3 1a
d2 a4 1b
c2 a1 1a
c1 b2 1c
b1 d1 1a
b1 a2 1b
ab d 1a