Hadoop 進階課程

範例

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說明

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WordCount
說明： 
  用於字數統計

測試方法：
  將此程式運作在hadoop 0.20 平台上，執行：
  ---------------------------
  hadoop jar WordCount.jar <input> <output>
  ---------------------------

注意：
1.  在hdfs 上來源檔案的路徑為 你所指定的 <input>
請注意必須先放資料到此hdfs上的資料夾內，且此資料夾內只能放檔案，不可再放資料夾
2.  運算完後，程式將執行結果放在hdfs 的輸出路徑為 你所指定的 <output>

WordCount.java

package org.nchc.hadoop;
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 {
    // eclipse using
//    String[] argv = { "/user/hadoop/input", "/user/hadoop/output-wc" };
//    args = argv;
    
    Configuration conf = new Configuration();
    
    String[] otherArgs = new GenericOptionsParser(conf, args)
        .getRemainingArgs();
    if (otherArgs.length != 2) {
      System.err
          .println("Usage: hadoop jar WordCount.jar <input> <output>");
      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(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
    CheckAndDelete.checkAndDelete(args[1], conf);
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}