import org.apache.hadoop.mapreduce.*; import org.apache.hadoop.io.*; public class MyMapper extends Mapper<LongWritable, Text, Text, IntWritable> { @Override public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException { @MyAnnotation String data = value.toString(); // ... context.write(new Text(data), new IntWritable(1)); } }