hadoop开发第一步

使用idea开发第一个hadoop程序：WordCount

一，打开idea，建立maven程序

二，添加基础依赖（pom.xml)

maven依赖版本查询网址:

https://mvnrepository.com/

    
        org.apache.hadoop
        hadoop-core
        1.2.1
    
    
        org.apache.hadoop
        hadoop-common
        2.7.2
    

三，编写主程序WordCount.java

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.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;

public class WordCount {

    public static class TokenizerMapper
            extends Mapper {

        private final static IntWritable one = new IntWritable(1);
        private Text word = new Text();

        public void map(Object key, Text value, Context context
        ) throws IOException, InterruptedException {
            StringTokenizer itr = new StringTokenizer(value.toString());
            while (itr.hasMoreTokens()) {
                word.set(itr.nextToken());
                context.write(word, one);
            }
        }
    }

    public static class IntSumReducer
            extends Reducer {
        private IntWritable result = new IntWritable();

        public void reduce(Text key, Iterable values,
                           Context context
        ) throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable val : values) {
                sum += val.get();
            }
            result.set(sum);
            context.write(key, result);
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf, "word count");
        job.setJarByClass(WordCount.class);
        job.setMapperClass(TokenizerMapper.class);
        job.setCombinerClass(IntSumReducer.class);
        job.setReducerClass(IntSumReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}

四，在src同级增加input文件夹，并添加多个文件，文件名不限（本例中文件为：001，002，）

         文件中内容：adu  hello等随便一些单词

五，配置运行参数：

          在idea菜单栏中选择Run->Edit Configurations，在弹出来的对话框中点击+，新建一个Application配置。配置Main class               为 WordCount（可以点击右边的...选择）

        program arguments为： input/   output/

          

       只修改main class和program arguments两个参数即可

 六，点击run运行，会生成output文件夹，与input同级（包含四个文件）

      

结果保存在part-r-00000文件中

hadoop权威指南中数据集链接

https://www1.ncdc.noaa.gov/pub/data/noaa/