Mapreduce实战-求每年最高气温

1.项目文件：

2014010114

2014010216

2014010317

2014010410

2014010506

2012010609

2012010732

2012010812

2012010919

2012011023

2001010116

2001010212

2001010310

2001010411

2001010529

2013010619

2013010722

2013010812

2013010929

2013011023

2008010105

2008010216

2008010337

2008010414

2008010516

2007010619

2007010712

2007010812

2007010999

2007011023

2010010114

2010010216

2010010317

2010010410

2010010506

2015010649

2015010722

2015010812

2015010999

2015011023

2.源代码

import java.io.IOException;
 
import org.apache.hadoop.conf.Configuration;
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.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;
 
public class Temperature {
    /**
     * 四个泛型类型分别代表：
     * KeyIn        Mapper的输入数据的Key，这里是每行文字的起始位置（0,11,...）
     * ValueIn      Mapper的输入数据的Value，这里是每行文字
     * KeyOut       Mapper的输出数据的Key，这里是每行文字中的“年份”
     * ValueOut     Mapper的输出数据的Value，这里是每行文字中的“气温”
     */
    static class TempMapper extends
            Mapper<LongWritable, Text, Text, IntWritable> {
        @Override
        public void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            // 打印样本: Before Mapper: 0, 2000010115
            System.out.print("Before Mapper: " + key + ", " + value);
            String line = value.toString();
            String year = line.substring(0, 4);
            int temperature = Integer.parseInt(line.substring(8));
            context.write(new Text(year), new IntWritable(temperature));
            // 打印样本: After Mapper:2000, 15
            System.out.println(
                    "======" +
                    "After Mapper:" + new Text(year) + ", " + new IntWritable(temperature));
        }
    }
 
    /**
     * 四个泛型类型分别代表：
     * KeyIn        Reducer的输入数据的Key，这里是每行文字中的“年份”
     * ValueIn      Reducer的输入数据的Value，这里是每行文字中的“气温”
     * KeyOut       Reducer的输出数据的Key，这里是不重复的“年份”
     * ValueOut     Reducer的输出数据的Value，这里是这一年中的“最高气温”
     */
    static class TempReducer extends
            Reducer<Text, IntWritable, Text, IntWritable> {
        @Override
        public void reduce(Text key, Iterable<IntWritable> values,
                Context context) throws IOException, InterruptedException {
            int maxValue = Integer.MIN_VALUE;
            StringBuffer sb = new StringBuffer();
            //取values的最大值
            for (IntWritable value : values) {
                maxValue = Math.max(maxValue, value.get());
                sb.append(value).append(", ");
            }
            // 打印样本： Before Reduce: 2000, 15, 23, 99, 12, 22, 
            System.out.print("Before Reduce: " + key + ", " + sb.toString());
            context.write(key, new IntWritable(maxValue));
            // 打印样本： After Reduce: 2000, 99
            System.out.println(
                    "======" +
                    "After Reduce: " + key + ", " + maxValue);
        }
    }
 
    public static void main(String[] args) throws Exception {
        //输入路径
        String dst = "hdfs://localhost:9000/intput.txt";
        //输出路径，必须是不存在的，空文件加也不行。
        String dstOut = "hdfs://localhost:9000/output";
        Configuration hadoopConfig = new Configuration();
         
        hadoopConfig.set("fs.hdfs.impl", 
            org.apache.hadoop.hdfs.DistributedFileSystem.class.getName()
        );
        hadoopConfig.set("fs.file.impl",
            org.apache.hadoop.fs.LocalFileSystem.class.getName()
        );
        Job job = new Job(hadoopConfig);
         
        //如果需要打成jar运行，需要下面这句
        //job.setJarByClass(NewMaxTemperature.class);
 
        //job执行作业时输入和输出文件的路径
        FileInputFormat.addInputPath(job, new Path(dst));
        FileOutputFormat.setOutputPath(job, new Path(dstOut));
 
        //指定自定义的Mapper和Reducer作为两个阶段的任务处理类
        job.setMapperClass(TempMapper.class);
        job.setReducerClass(TempReducer.class);
         
        //设置最后输出结果的Key和Value的类型
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
         
        //执行job，直到完成
        job.waitForCompletion(true);
        System.out.println("Finished");
    }
}

3.运行页面