mapper类的代码：

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实现Mapper类的方法

import java.io.IOException;

import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.LongWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Mapper;

public class MyMapper extends Mapper {

// constant

private static final int MISSING = 9999;

// map function

@Override

protected void map(LongWritable key, Text value, Mapper.Context context)

throws IOException, InterruptedException {

// per line

String line = value.toString();

// get year

String year = line.substring(15, 19);

// get airtemp

int airTemperature;

if (line.charAt(87) == '+') {

airTemperature = Integer.parseInt(line.substring(88, 92));

} else {

airTemperature = Integer.parseInt(line.substring(87, 92));

}

// valid air temp data

String quality = line.substring(92, 93);

if (airTemperature != MISSING && quality.matches("[01459]")) {

context.write(new Text(year), new IntWritable(airTemperature));

}

}

}

Reduce类的代码：

实现Reducer类的方法

import java.io.IOException;

import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Reducer;

public class MyReducer extends Reducer {

@Override

protected void reduce(Text key, Iterable values, Context context)

throws IOException, InterruptedException {

// max

int maxValue = Integer.MIN_VALUE;

// for

for (IntWritable value : values) {

maxValue = Math.max(maxValue, value.get());

}

// output

context.write(key, new IntWritable(maxValue));

}

}

主方法的代码：

import mapper类实现.MyMapper;

import reducer类实现.MyReducer;

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;

public class MyMapperApp {

/**

* @param args

* @throws Exception

* @throws IllegalArgumentException

*/

public static void main(String[] args) throws IllegalArgumentException, Exception {

// new job

Job job = Job.getInstance();

// find jar by ClassName

job.setJarByClass(MyMapper.class);

// job name

job.setJobName("Max temperature");

FileInputFormat.addInputPath(job, new Path("file:///mnt/hgfs/test-ncdc-data"));

FileOutputFormat.setOutputPath(job, new Path("file:///home/hadoop/mr/"));

job.setMapperClass(MyMapper.class);

job.setReducerClass(MyReducer.class);

job.setOutputKeyClass(Text.class);

job.setOutputValueClass(IntWritable.class);

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

}

}

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