mapreduce求ncdc气象数据中最低温度

数据准备
在ftp://ftp.ncdc.noaa.gov/pub/data/平台下载gsod目录下的2016和2017年的数据，然后放在linux的任何目录下
1.使用如下命令解压gsod_2016和gsod_2017这两个压缩包

tar -xvf gsod_2016.tar
tar -xvf gsod_2017.tar

2.使用zcat命令把这些数据文件解压并合并到一个ncdc.txt文件中，并且可以查看

zcat *.gz > ncdc.txt
ll |grep ncdc

3.去除标题行，然后查看结果

sed -i '/STN/d' ncdc.txt
head -12 ncdc.txt

4.在hdfs上面创建一个目录in，并且将那个ncdc.txt文件上传到hdfs

./bin/hdfs dfs -mkdir /in
./bin/hdfs dfs -put /home/hadoop/gsod/ncdc.txt /in
./bin/hdfs dfs -ls /in  #查看/in目录下的ncdc.txt文件 

5.准备好以下三个java脚本文件
MinTemperature.java

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 MinTemperature {  
    
    public static void main(String[] args) throws Exception {  
       if(args.length != 2) {  
           System.err.println("Usage: MinTemperature 
");  
            System.exit(-1);  
       }  
         
       Job job = new Job();  
       job.setJarByClass(MinTemperature.class);  
       job.setJobName("Min temperature");  
       FileInputFormat.addInputPath(job, new Path(args[0]));  
       FileOutputFormat.setOutputPath(job, new Path(args[1]));  
       job.setMapperClass(MinTemperatureMapper.class);  
       job.setReducerClass(MinTemperatureReducer.class);  
       job.setOutputKeyClass(Text.class);  
       job.setOutputValueClass(IntWritable.class);  
       System.exit(job.waitForCompletion(true) ? 0 : 1);  
   } 
} 

MinTemperatureMapper.java

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 MinTemperatureMapper extends Mapper{  
   
   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(14, 18);  
         
       int airTemperature;
      
       airTemperature =(int)Math.floor(Double.valueOf(line.substring(24, 30).trim())); 
        
       if(airTemperature != MISSING ) 
       {
           context.write(new Text(year), new IntWritable(airTemperature));  
       }  
   }  
}  

MinTemperatureReducer.java

import java.io.IOException;  
import org.apache.hadoop.io.IntWritable;  
import org.apache.hadoop.io.Text;  
import org.apache.hadoop.mapreduce.Reducer;  
   
public class MinTemperatureReducer extends Reducer {  
  
    @Override  
   public void reduce(Text key, Iterable values, Context context) throws IOException, InterruptedException {  
         
        int minValue = Integer.MAX_VALUE;  
        for(IntWritable value : values) {  
            minValue = Math.min(minValue, value.get());  
       }  
        context.write(key, new IntWritable(minValue));  
    }  
}  

6.以上三个java文件写完将其Export为.jar文件并且保存在/usr/local/hadoopmyapp这个目录下，将这个文件名字命名为MinTempearture


7.可以在/usr/local/hadoop上的myapp目录下查看压缩包是否存在并开启hadoop平台

8.运行如下命令运行.jar这个文件

cd /usr/local/hadoop
./bin/hadoop jar ./myapp/MinTempearture.jar /in/ncdc.txt /ncdc

注意：/in/ncdc.txt是事先上传到hdfs的文件，/ncdc是程序运行结束才有的文件

9.查看文件写入情况

如上图所示已经生成了ncdc这个目录，但是运行结果看不到，在linux输入如下命令查看

cd /usr/local/hadoop
./bin/hdfs dfs -ls /ncdc
./bin/hdfs dfs -cat /ncdc/part-r-00000

如下图所示：

运行成功，最低气温2016年是-112，2017年是-115.