Hadoop使用MapReduce求ncdc气象数据中的最低温度
一、下载、解压、合并与上传数据
在进行数据处理前首先需要获得所需要的数据，首先下载数据
cd /home/hadoop
mkdir temp #创建文件夹用于存放数据
cd temp
sudo wget ftp://ftp.ncdc.noaa.gov/pub/data/gsod/2016/gsod_2016.tar
sudo wget ftp://ftp.ncdc.noaa.gov/pub/data/gsod/2017/gsod_2017.tar
解压2016与2017年的数据包
tar -xvf gsod_2016.tar
tar -xvf gsod_2017.tar
将这些数据文件解压并合并到一个ncdc.txt文件中
zcat *.gz > ncdc.txt
ll |grep ncdc
显示如下内容
-rw-rw-r-- 1 hadoop hadoop 1133436858 11月 12 15:54 ncdc.txt
查看ncdc.txt文件
head -12 ncdc.txt
显示如下内容
007026 99999 20160622 94.7 7 66.7 7 9999.9 0 9999.9 0 6.2 4 0.0 7 999.9 999.9 100.4* 87.8* 0.00I 999.9 000000
007026 99999 20160623 88.3 24 69.7 24 9999.9 0 9999.9 0 6.2 24 0.0 24 999.9 999.9 98.6* 78.8* 0.00I 999.9 000000
007026 99999 20160624 80.5 24 69.3 24 9999.9 0 9999.9 0 5.8 22 0.0 24 999.9 999.9 93.2* 69.8* 99.99 999.9 010000
007026 99999 20160625 81.4 24 71.8 24 9999.9 0 9999.9 0 5.9 23 0.0 24 999.9 999.9 89.6* 73.4* 0.00I 999.9 000000
007026 99999 20160626 80.5 24 63.4 24 9999.9 0 9999.9 0 6.2 22 0.0 24 999.9 999.9 91.4* 69.8* 0.00I 999.9 000000
007026 99999 20160627 80.6 24 64.2 24 9999.9 0 9999.9 0 6.0 23 0.0 24 999.9 999.9 93.2* 68.0* 0.00I 999.9 000000
007026 99999 20160628 77.4 24 70.8 24 9999.9 0 9999.9 0 5.1 17 0.0 24 999.9 999.9 87.8* 71.6* 99.99 999.9 010000
007026 99999 20160629 74.3 16 71.9 16 9999.9 0 9999.9 0 2.7 13 0.0 16 999.9 999.9 86.0* 69.8* 0.00I 999.9 000000
007026 99999 20170210 46.9 11 19.4 11 9999.9 0 9999.9 0 6.2 11 3.6 11 8.0 13.0 53.6* 35.6* 0.00I 999.9 000000
007026 99999 20170211 54.4 24 35.0 24 9999.9 0 9999.9 0 6.2 24 4.7 24 12.0 21.0 77.0* 42.8* 0.00I 999.9 000000
007026 99999 20170212 70.2 24 52.9 24 9999.9 0 9999.9 0 6.2 24 5.2 24 15.0 21.0 84.2* 62.6* 0.00I 999.9 000000
007026 99999 20170213 61.1 22 35.4 22 9999.9 0 9999.9 0 6.2 22 8.9 22 15.0 24.1 75.2* 50.0* 0.00I 999.9 000000
使用sed命令删除匹配'STN'的行
sed -i '/STN/d' ncdc.txt
将准备好的数据上传至hdfs
cd /usr/local/hadoop/sbin
start-all.sh
cd /usr/local/hadoop/bin
hadoop fs -copyFromLocal /home/hadoop/temp/ncdc.txt input
如果此前未在hdfs中创建input文件夹可用如下指令创建
hadoop fs -mkdir input
二、编写求最低温度的MapReduce代码
首先去/home/hadoop/temp目录下创建文件夹code以保存本地代码
cd /home/hadoop/temp
mkdir code
cd code
编写MinTemperature.java
vim MinTemperature.java
输入以下代码，然后保存并退出
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<input path> <output path>");
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);
}
}
编写MinTemperatureMapper.java
vim MinTemperatureMapper.java
输入以下代码，然后保存并退出
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<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(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));
}
}
编写MinTemperatureReducer.java
vim MinTemperatureReducer.java
输入以下代码，然后保存并退出
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<Text, IntWritable, Text, IntWritable>
{
@Override
public void reduce(Text key, Iterable<IntWritable> 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));
}
}
三、编译运行程序
首先编译所有.java文件
javac *.java
如果遇到编译失败或显示API过时可用以下指令重新编译
javac -Xlint:deprecation *.java
将.class文件打包成jar包
jar cvf ./MinTemperature.jar ./*.class
执行程序
cd /usr/local/hadoop/bin
hadoop jar /home/hadoop/temp/code/MinTemperature.jar MinTemperature input/ncdc.txt ncdc
查看结果
hadoop fs -cat ncdc/part-r-00000
执行结果如下图所示
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