java - Hadoop : Reducer class not called even with Overrides

Question

我在 hadoop 中尝试了 mapreduce wordcount 代码，但是 reducer 类从未被调用，程序在运行 mapper 类后终止。

import java.io.IOException;
import java.util.*;

import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

public class WordCount {

 public static class Map extends Mapper<LongWritable, Text, Text, IntWritable> {
    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();
    @Override 
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String line = value.toString();
        StringTokenizer tokenizer = new StringTokenizer(line);
        while (tokenizer.hasMoreTokens()) {
            word.set(tokenizer.nextToken());
            context.write(word, one);
        }
    }
 } 

 public static class Reduce extends Reducer<Text, IntWritable, Text, IntWritable> {


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

 public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();

        Job job = new Job(conf, "wordcount");

    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);

    job.setMapperClass(Map.class);
    job.setReducerClass(Reduce.class);

    job.setInputFormatClass(TextInputFormat.class);
    job.setOutputFormatClass(TextOutputFormat.class);

    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));

    job.waitForCompletion(true);
 }

}

我什至根据需要覆盖了类。

集成开发环境:Eclipse Luna
Hadoop:版本 2.5

Answer 1

Job 对象构成了作业的规范，并使您可以控制作业的运行方式。当我们在 Hadoop 集群上运行此作业时，我们会将代码打包到一个 JAR 文件中(Hadoop 将在集群中分发该文件)。

我们可以在 Job 的 setJarByClass() 方法中传递一个类，而不是显式指定 JAR 文件的名称，Hadoop 将使用该类通过查找包含该类的 JAR 文件来定位相关的 JAR 文件。

我没有在 main 方法中看到语句。因此，包含它然后编译并运行代码。

job.setJarByClass(WordCount.class);