public class MedianeLongueurLignesEtape1Mapper
   extends Mapper<LongWritable, Text, IntWritable, LongWritable>
{
   private final LongWritable valeurI = new LongWritable(1L);
   private IntWritable cleI = new IntWritable();
   @Override
   public void map(LongWritable cleE, Text valeurE, Context context)
        throws IOException, InterruptedException
   {
      cleI.set(valeurE.getLength());
      context.write(cleI, valeurI);
   }
}