public class TraitementMapper
        extends Mapper<TypCleE,TypValE, TypCleI,TypValI>
{
    @Override
    public void map(TypCleE cleE, TypValE valE,
                Context context) throws Exception
    {
        /** traitement: cleI = ..., valI = ... **/
        TypCleI cleI = new TypCleI(...);
        TypValI valI = new TypValI(...);
        context.write(cleI, valI);
    }
}