1、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
提交到本地執行：開發過程中使用

2、WordCountApp.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
 *
 * 提交到本地執行：開發過程中使用
 
 
*/

public class WordCountApp {

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

        //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");

        
 
//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(WordCountApp.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("/wordcount/input"));
        FileOutputFormat.setOutputPath(job, new Path("/wordcount/output"));

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

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

    }
    //若輸出失敗，新增以下程式碼
    static {

        try {
            //G:\BaiduNetdiskDownload\hadoop2.7.6\bin\hadoop.dll
            System.load("G:\\BaiduNetdiskDownload\\hadoop2.7.6\\bin\\hadoop.dll");

        } catch (UnsatisfiedLinkError e) {

            System.err.println("Native code library failed to load.\n" + e);

            System.exit(1);

        }

    }
}

3、log4j.properties

由於日誌中不報錯，新增後，可檢視錯誤原因

在resources中新建file

log4j.rootLogger=INFO,stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=[%-5p] method:%l%n%m%n

4、在命令列中多層新建input資料夾，並放入檔案h.txt

5、執行