public Builder<T> addIntComparator(final String fieldId,
                                               final ToIntFunction<T> extractor) {
                Objects.requireNonNull(fieldId);
                Objects.requireNonNull(extractor);
                comparatorMap.put(
                        fieldId,
                        new CaseAgnosticComparator<>(Comparator.comparingInt(extractor)));
                return this;
            }
Adds a single comparator for fieldId, using extractor to provide the value.
stroom-util-shared/src/main/java/stroom/util/shared/CompareUtil.java