MapReduce编程规范（三）

public class WordCount {

   public static enum Counters {
      INPUT_WORDS
   }

   public static class WordCountMapper 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 {
         String[] words = value.toString().split(" ");
         for (String w : words) {
            word.set(w);
            context.write(word, one);
            context.getCounter(Counters.INPUT_WORDS).increment(1);
         }
      }
   }

   public static class WordCountReducer 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();
      Job job = Job.getInstance(conf, "word count");
      job.setJarByClass(WordCount.class);
      job.setMapperClass(WordCountMapper.class);
      job.setCombinerClass(WordCountReducer.class);
      job.setReducerClass(WordCountReducer.class);
      job.setOutputKeyClass(Text.class);
      job.setOutputValueClass(IntWritable.class);
      FileInputFormat.addInputPath(job, new Path(args[0]));
      FileOutputFormat.setOutputPath(job, new Path(args[1]));
      System.exit(job.waitForCompletion(true) ? 0 : 1);
   }
}