Hadoop MapReduce开发--平均值

测试数据：

china.txt

张三    78
李四    89
王五    96
赵六    67

english.txt

张三    80
李四    82
王五    84
赵六    86

math.txt

张三    88
李四    99
王五    66
赵六    77

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;

public class AvgMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String line = value.toString();
        if (line.trim().length() > 0) {
            String[] arr = line.split("\t");
            if (arr.length == 2) {
                context.write(new Text(arr[0]), new IntWritable(Integer.valueOf(arr[1])));
            }
        }
    }
}

reducer代码：

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

import java.io.IOException;

public class AvgReducer extends Reducer<Text, IntWritable, Text, DoubleWritable> {
    @Override
    protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        int sum = 0;
        for(IntWritable val : values) {
            sum += val.get();
        }
        context.write(key, new DoubleWritable(Double.valueOf(String.format("%.2f", sum / 3.0))));
    }
}

main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.DoubleWritable;
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平均值处理。
 */
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();
        Job job = Job.getInstance(conf, "avg job");
        job.setJarByClass(Job.class);

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

        job.setReducerClass(AvgReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(DoubleWritable.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：

张三    82.0
李四    90.0
王五    82.0
赵六    76.67