使用MapReduce统计天气数据中的最高气温

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使用MapReduce统计天气数据中的最高气温

例子是从Hadoop权威指南上改写的，需要先将代码生成jar包，然后将测试样例和jar包上传到HDFS中，使用命令运行，最终会得出每年的最高气温统计结果，运行命令不写出来了。代码也很简单，就是分别写出map和reduce的操作，map中对数据进行一个分割，提取，将结果传给reduce进行统计。

package com.rain.mapreduce;

import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;

import java.io.IOException;

/**
 * Hadoop书上的最高气温判断
 */
public class MaxTemperature {
    public static class MaxTemperatureMapper extends  Mapper<LongWritable,Text, Text, IntWritable>{

        private static final int MISSING = 9999;

        @Override
        public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            String line = value.toString();
            String year = line.substring(15,19);
            int airTemperature;
            if (line.charAt(87) == '+') {
                airTemperature = Integer.parseInt(line.substring(88,92));
            }else{
                airTemperature = Integer.parseInt(line.substring(87,92));
            }
            String quality = line.substring(92,93);
            if (airTemperature!=MISSING&&quality.matches("[01459]")){
                context.write(new Text(year), new IntWritable(airTemperature));
            }

        }
    }
    public static class MaxTemperatureReducer extends Reducer<Text ,IntWritable,Text,IntWritable>{
        @Override
        protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
            int maxValue = Integer.MIN_VALUE;
            for (IntWritable value:values){
                maxValue = Math.max(maxValue,value.get());
            }
            context.write(key,new IntWritable(maxValue));

        }
    }
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        if (args.length!=2){
            System.err.println("Usage:MaxTEmperature");
            System.exit(-1);
        }
        Job job = new Job();
        job.setJarByClass(MaxTemperature.class);
        job.setJobName("Max temperature");


        FileInputFormat.addInputPath(job,new Path(args[0]));
        FileOutputFormat.setOutputPath(job,new Path(args[1]));

        job.setMapperClass(MaxTemperatureMapper.class);
        job.setReducerClass(MaxTemperatureReducer.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

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