MapReduce实验——topN排名

package topN_01;

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

import java.io.IOException;
import java.util.Arrays;

public class MyMap extends
        Mapper {
    int len;
    int[] top;
    @Override
    protected void setup(Context context){
        //这个是从配置文件中,获得N的个数，如果没有设置这个变量，默认的是10
        len = context.getConfiguration().getInt("N",10);
        top = new int[len+1];
    }

    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String[] arr = value.toString().split(",",-1);
        if(arr.length == 4){
            int x = Integer.valueOf(arr[2]);
            add(x);
        }
    }

    protected void add(int val){
        //专门用来存放放进来的数据
        top[0] = val;
        //排序，从小到大排序，top初始值都是0
        Arrays.sort(top);
    }

    @Override
    protected void cleanup(Context context) throws IOException, InterruptedException {
        for (int i = 1; i < len+1; i++) {
            context.write(new IntWritable(top[i]),new IntWritable(top[i]));
        }
    }
}

package topN_01;

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

import java.io.IOException;
import java.util.Arrays;

public class MyReduce extends Reducer {
    int len;
    int[] top;
    @Override
    protected void setup(Context context){
        //这个是从配置文件中,获得N的个数，如果没有设置这个变量，默认的是10
        len = context.getConfiguration().getInt("N",10);
        top = new int[len+1];
    }
    @Override
    protected void reduce(IntWritable key,Iterable values,Context context){
        for (IntWritable val: values) {
            add(val.get());
        }
    }
    protected void add(int val){
        top[0] = val;
        Arrays.sort(top);
    }
    @Override
    protected void cleanup(Context context) throws IOException, InterruptedException {
        for (int i = len; i > 0 ; i--) {
            //从最大值开始正序排序
            context.write(new Text(String.valueOf(len -i + 1)),new Text(String.valueOf(top[i])));
        }
    }
}

package topN_01;

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

import org.apache.hadoop.io.Text;
import java.io.IOException;

public class TestJob {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        Configuration conf = new Configuration();
        //1 get a job
        Job job = Job.getInstance(conf);
        //2 set jar main class
        job.setJarByClass(TestJob.class);
        //3 set map class and reducer class
        job.setMapperClass(MyMap.class);
        job.setReducerClass(MyReduce.class);
        //4 set map reduce output type
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongWritable.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(LongWritable.class);
        //5 set key/value output file format and input/output path
        FileInputFormat.setInputPaths(job,new Path("file:///simple/word.txt"));
        FileOutputFormat.setOutputPath(job,new Path("file:///simple/result"));
        //6 commit job
        job.waitForCompletion(true);
    }
}