Java重写MapReduce

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package com.shujia.mr;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
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;
import java.io.IOException;

public class MR01 {
    
    public static class WordMapper extends Mapper{
        @Override
        protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            String line =value.toString();//相对每行数据处理，Text转化为String
            int v=1;
            context.write(new Text(line),new LongWritable(v));
        }
    }
    
    public static class WordReducer extends Reducer{
        @Override
        protected void reduce(Text key, Iterable values, Context context) throws IOException, InterruptedException {
            int count=0;
            for (LongWritable value : values) {
                count+=value.get();//.get()是将LongWritable转为int类型
            }
            context.write(key,new LongWritable(count));
        }
    }

    public static void main(String[] args) throws Exception{
        //配置mapreduce
        Job job = Job.getInstance();
        job.setJobName("第一个mr程序 单词统计");
        job.setJarByClass(MR01.class);
        //map段所在类的位置
        job.setMapperClass(WordMapper.class);
        //reduce段所在类的位置
        job.setReducerClass(WordReducer.class);
        //指定map段kv的输出类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongWritable.class);
        //指定reduce段kv的输出类型
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(LongWritable.class);
        //指定路径
        Path input = new Path("/words.txt");
        Path out = new Path("/output");
        //输出路径不能已存在，手动加上 已存在删除
        FileSystem fs = FileSystem.get(new Configuration());
        if(fs.exists(out)){
            fs.delete(out,true);
        }
        FileInputFormat.addInputPath(job,input);
        FileOutputFormat.setOutputPath(job,out);
        //启动
        job.waitForCompletion(true);
        System.out.println("正在运行mr");
    }
}

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