code: public <T> T queryColumns(K key, List<N> columns,
        ColumnFamilyRowMapper<K, N, T> mapper) {
      HSlicePredicate<N> predicate = new HSlicePredicate<N>(topSerializer);
      predicate.setColumnNames(columns);        
      return doExecuteSlice(key, predicate, mapper);
    }
docs: Queries all columns at a given key and maps them to an object of type OBJ
  using the given mapping object
  
  @param <T>
  @param key
  @param columns
  @param mapper
  @return