敲了一下hadoop权威指南第二章的例题，虽然基本上是照着书上敲的，但还是把它放到这方便以后查看。

代码如下：

<span style="font-size:18px;"><span style="font-size:18px;">import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

public class MaxTemperature {

	  static class MaxTemperatureMapper
	        extends Mapper<LongWritable, Text, Text ,IntWritable >{
		    private static final int MISSING = 9999;
		    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(29) == '+'){
		    		airTemperature  = Integer.parseInt(line.substring(30, 35));
		    	}
		    	else{
		    		airTemperature = Integer.parseInt(line.substring(29, 35));
		    	}
		    	String quality = line.substring(35, 36);
		    	if(airTemperature != MISSING && quality.matches("[01459]"));{
		    		context.write(new Text(year), new IntWritable(airTemperature));
		    	}
		    }
	  }
	  
	  
	  static class MaxTemperatureReducer 
	     extends Reducer <Text , IntWritable, Text, IntWritable>{
		 public void reduce (Text key, Iterable<IntWritable> values,
				 Context context)
				 throws IOException, InterruptedException{
			 
			 int maxValue =  http://www.mamicode.com/Integer.MIN_VALUE;>

输出结果如下（输入数据是自己随便造的，输出的所有气温值都乘了10）


Hadoop权威指南---第二章MaxTemperature例题源码