1、上述的MapReduce之Mapper、Reducer、Driver三步實現，是基於輸入和輸出都是HDFS的

（1）輸入：HADOOP_USER_NAME、
（2）輸出：hdfs://192.168.126.101:8020

//WordCountApp.java       
        //設定許可權
        System.setProperty("HADOOP_USER_NAME", "hadoop");

        Configuration configuration = new Configuration();
        //在configuration裡設定一些東西：
        configuration.set("fs.defaultFS", "hdfs://192.168.126.101:8020");
        
 

2、不連HDFS，只在本地處理詞頻統計

（1）在hadoop-train-v2下新建Directory：input

（2）在input裡新建file.text：WordCount.Input

（3）將h.txt內容考入WordCount.Input中

（4）在com.imooc.bigdata.hadoop.mapreduce.wordcount下複製WordCountApp.java為：WordCountLocalApp.java

3、WordCountLocalApp.java

package com.imooc.bigdata.hadoop.mapreduce.wordcount;


 
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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

 
/*
 * Driver類：配置Mapper和Reducer的相關屬性
 * 通過WordCountApp.java將Mapper和Reducer關聯起來
 * 使用MapReduce統計HDFS上的檔案對應的詞頻
 *
 * 使用本地檔案進行統計，然後統計結果輸出到本地路徑
 */

public class WordCountLocalApp {

    public static void main(String[] args) throws Exception{

        Configuration configuration = new Configuration();

        //建立一個Job
        //將configuration傳進來
        Job job = Job.getInstance(configuration);

        //設定Job對應的引數：主類
        job.setJarByClass(WordCountLocalApp.class);

        //設定Job對應的引數：設定自定義的Mapper和Reducer處理類
        job.setMapperClass(WordCountMapper.class);
        job.setReducerClass(WordCountReducer.class);

        //設定Job對應的引數：Mapper輸出key和value的型別
        //不需要關注Mapper輸入
        //Mapper<LongWritable, Text, Text, IntWritable>
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);

        //設定Job對應的引數：Reducer輸出key和value的型別
        //不需要關注Reducer輸入
        //Reducer<Text, IntWritable, Text, IntWritable>
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        //設定Job對應的引數：Mapper輸出key和value的型別：作業輸入和輸出的路徑
        FileInputFormat.setInputPaths(job, new Path("input"));
        FileOutputFormat.setOutputPath(job, new Path("output"));

        //提交job
        boolean result = job.waitForCompletion(true);

        System.exit(result ? 0 : -1);

    }

}

4、結果輸出

問題：統計結果區分大小寫