四.idea本地调试hadoop程序

目录：

目录见文章1

1.先上案例代码

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;
import org.apache.hadoop.util.GenericOptionsParser;

public class WordCount {
//WordCOuntMap方法接收LongWritable，Text的参数，返回<Text， IntWriatable>键值对。
  public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable>{
    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<Text,IntWritable,Text,IntWritable> {
    private IntWritable result = new IntWritable();

    public void reduce(Text key, Iterable<IntWritable> 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 {
    System.setProperty("hadoop.home.dir", "D:\hadoop-2.7.6");//这一行一定要
    Configuration conf = new Configuration();
    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
    if (otherArgs.length != 2) {
      System.err.println("Usage: wordcount <in> <out>");
      System.exit(2);
    }
    Job job = new Job(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(otherArgs[0]));
    FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

如下图，至于NativeIO，可从https://download.csdn.net/download/xiaoliu123586/10551225里下载

2.新建input文件夹，里面放w.txt

yaojiale hahaha 
yaojiale llllll 

3.运行时可能的报错

需要加winutils.exe,libwinutils.lib 拷贝到%HADOOP_HOME%in目录 ，可能还要下载hadoop.dll，并拷贝到c:windowssystem32目录中。

以上所需，可在https://download.csdn.net/download/xiaoliu123586/10551225里下载

附：eclipse 中运行 Hadoop2.7.3 map reduce程序 出现错误(null) entry in command string: null chmod 0700

4.运行加main参数：input output5

分别代表读取本地本项目input文件夹（内有w.txt,见图一），以及输出到output5文件夹

5.至于网上说的project structure>module>添加本地hadoop jar包，这个不是必须，比如，使用maven pom.xml的话，就能得到库支持 ，

而上述把winutils.exe等东西 添加到本地hadoop_home下（bin下）（如，我的是 D:/hadoop-2.7.6/），

使添加进去的东西起作用的，是以下代码：

System.setProperty("hadoop.home.dir", "D:\hadoop-2.7.6");