1.MapReduce計算框架

2.例項WordCount

package org.apache.hadoop.examples;
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.mapred.TextInputFormat;
import org.apache
 
.hadoop.mapred.TextOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;
public class WordCount {

  // This is the Mapper class
  public static class TokenizerMapper 
       extends Mapper<Object, Text, Text, IntWritable>{
    //define IntWritaable class object one
    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 IntSumCombiner
       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);
    }
  }

  // This is the Reducer class
  // count of word = count set output format
  public static class IntSumReducer
       extends Reducer<Text,IntWritable,Text,Text> {

    private Text result_key= new Text();
    private Text result_value= new Text();
    private byte[] prefix;
    private byte[] suffix;

    protected void setup(Context context) {
      try {
        prefix= Text.encode("count of ").array();
        suffix= Text.encode(" =").array();
      } catch (Exception e) {
        prefix = suffix = new byte[0];
      }
    }

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

      // generate result key
      result_key.set(prefix);
      result_key.append(key.getBytes(), 0, key.getLength());
      result_key.append(suffix, 0, suffix.length);

      // generate result value
      result_value.set(Integer.toString(sum));

      context.write(result_key, result_value);
    }
  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    System.out.println("conf information:  "+conf.toString());
    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
    System.out.println("otherArgs:");
    for(int i=0;i<otherArgs.length;i++)
        System.out.println(otherArgs[i]);
    if (otherArgs.length < 2) {
      System.err.println("Usage: wordcount <in> [<in>...] <out>");
      System.exit(2);
    }

    Job job = Job.getInstance(conf, "word count");

    job.setJarByClass(WordCount.class);

    job.setMapperClass(TokenizerMapper.class);
    job.setCombinerClass(IntSumCombiner.class);
    job.setReducerClass(IntSumReducer.class);

    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(IntWritable.class);

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

    // add the input paths as given by command line
    for (int i = 0; i < otherArgs.length - 1; ++i) {
      FileInputFormat.addInputPath(job, new Path(otherArgs[i]));
      System.out.println("==================================");
      System.out.println(otherArgs[i]);
    }
    System.out.println(otherArgs[otherArgs.length - 1]);
    // add the output path as given by the command line
    FileOutputFormat.setOutputPath(job,
      new Path(otherArgs[otherArgs.length - 1]));

    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}