hadoop-002-Eclipse 運行WordCount 案例

一、如過提示 eclipse 沒法編譯 文件 ，提示對某文件無權限。

chmod -R 777  workspace

二、在eclipse中跑Ｈadoop測試用例時，出現這樣的錯誤
Exception in thread "main" org.apache.hadoop.mapred.InvalidInputException: Input path does not exist: 

緣由是系統沒有找到hadoop的配置文件,
　對於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>

解決方法：

        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"));     

任選註釋掉代碼其中的一行執行便可。

完整代碼以下：

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);
  }
}

示意圖

參考資料

http://hadoop.apache.org/docs/r2.5.2/hadoop-project-dist/hadoop-common/SingleCluster.html#Standalone_Operation

http://zhidao.baidu.com/link?url=BGh7Ve3T2M63CqhDrvxItIFLKK9AubSr3K5lmdkDP6YpUtp4X3m0FaOFShK8lD10VQE5pokmklfI14QUImhITa

http://blog.csdn.net/duguduchong/article/details/8712733

http://blog.csdn.net/liou825/article/details/9966831