Chapter 4 of Hadoop Learning: statistical Test procedure for maximum temperature

1.测试温度数据下载：

http://down.51cto.com/data/2213610

2.将数据上传到hdfs中

3.测试代码为：

MinTemperature

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; publicclass MinTemperature { publicstaticvoid 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

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; publicclass MinTemperatureMapper extends Mapper{ privatestatic final intMISSING = 9999; @Override publicvoid 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)); } }}

MinTemperatureReducer

import java.io.IOException;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Reducer; publicclass MinTemperatureReducer extends Reducer { @Override publicvoid 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)); }}