Hadoop MapReduce开发--取TopN数据

测试数据：

file1.txt

1,9819,100,121
2,8918,2000,111
3,2813,1234,22
4,9100,10,1101
5,3210,490,111
6,1298,28,1211
7,1010,281,90
8,1818,9000,20

file2.txt

100,3333,10,100
101,9321,1000,293
102,3881,701,20
103,6791,910,30
104,8888,11,39
105,2345,880,40
106,1234,700,40

mapper代码

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 TOPNMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
    int len;
    int[] top;
    private static final Text KEY = new Text("K");

    @Override
    protected void setup(Context context) throws IOException, InterruptedException {
        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 line = value.toString().trim();
        String[] arr = line.split(",");
        if(arr.length > 0 && arr.length == 4) {
            int payment = Integer.valueOf(arr[2]);
            add(payment);
        }
    }

    private void add(int payment) {
        top[0] = payment;
        Arrays.sort(top);
    }

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

reducer代码

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 TOPNReducer extends Reducer<Text, IntWritable, IntWritable, IntWritable> {
    int len;
    int[] top;

    @Override
    protected void setup(Context context) throws IOException, InterruptedException {
        len = context.getConfiguration().getInt("N", 10);
        top = new int[len + 1];
    }

    @Override
    protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        for(IntWritable val : values) {
            int payment = val.get();
            add(payment);
        }
    }

    private void add(int payment) {
        top[0] = payment;
        Arrays.sort(top);
    }
    @Override
    protected void cleanup(Context context) throws IOException, InterruptedException {
        for(int i = len; i >= 1; i--) {
            context.write(new IntWritable(len - i + 1), new IntWritable(top[i]));
        }
    }
}

job代码

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

import java.io.IOException;

/**
 * 该案例对输入数据进行取前N最大值处理，降序排列。
 */
public class JobMain {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        if(args.length != 2) {
            System.err.println("Usage: MaxTemperature<input path> <output path>");
            System.exit(-1);
        }

        Configuration conf = new Configuration();
        conf.setInt("N", 5);
        Job job = Job.getInstance(conf, "TOP N job");
        job.setJarByClass(Job.class);

        job.setMapperClass(TOPNMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);

        job.setReducerClass(TOPNReducer.class);
        job.setOutputKeyClass(IntWritable.class);
        job.setOutputValueClass(IntWritable.class);

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

        Path outDirPath = new Path(args[1]);
        FileSystem fs = FileSystem.get(conf);
        if (fs.exists(outDirPath)) {
            fs.delete(outDirPath, true);
        }
        FileOutputFormat.setOutputPath(job, outDirPath);

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

结果：

1    9000
2    2000
3    1234
4    1000
5    910