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());   //（1）使用空格进行分词

       while (itr.hasMoreTokens()) {

         word.set(itr.nextToken());   //（2）把Token放入Text对象中

         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);   //（3）输出每个Token的统计结果

     }

   }

   public static void main(String[] args) throws Exception {

     Configuration conf = new Configuration();

     String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();

     if (otherArgs.length < 2) {

       System.err.println("Usage: wordcount <in> [<in>...] <out>");

       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);

     for (int i = 0; i < otherArgs.length - 1; ++i) {

       FileInputFormat.addInputPath(job, new Path(otherArgs[i]));

     }

     FileOutputFormat.setOutputPath(job,

       new Path(otherArgs[otherArgs.length - 1]));

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

   }

 }