hadoop-002-Eclipse 运行WordCount 案例-优快云博客

本文详细介绍了如何使用Hadoop实现WordCount程序，并解决了在Eclipse中运行Hadoop测试用例时出现的InvalidInputException错误。通过设置fs.defaultFS参数及正确配置core-site.xml文件，确保了Hadoop集群能够正常读取输入路径。

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1、如过提示 eclipse 无法编译文件，提示对某文件无权限。

chmod -R 777 workspace

2、在eclipse中跑Ｈadoop测试用例时，出现这样的错误
Exception in thread "main" org.apache.hadoop.mapred.InvalidInputException: Input path does not exist:

原因是系统没有找到hadoop的配置文件,
　对于2.5.2就是core-site.xml
其中指定了 fs.defaultFS的配置

<property>
<name>fs.defaultFS</name>
<value>hdfs://localhost:9000</value>
</property>

解决方法：

       JobConf conf = new JobConf(WordCount.class);
       conf.setJobName("wordcount");
       //conf.set("fs.defaultFS", "hdfs://localhost:9000");
       //conf.addResource(new Path("/opt/hadoop/etc/hadoop/core-site.xml"));

任选注释掉代码其中的一行执行即可。

完整代码如下：

package com.zwh;

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 {

  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 {
    Configuration conf = new Configuration();
    conf.set("fs.defaultFS", "hdfs://localhost:9000"); 
    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("/user/root/input/"));
    FileOutputFormat.setOutputPath(job,new Path("/user/root/output/wc"));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

示意图