filtersFlatMap.java

ImmutableList<String> filters = FluentIterable
                .from(taxonomyFieldConfig.getTaxonomyLevelConfigs())
                .transformAndConcat(new Function<TaxonomyLevelConfig, List<String>>() {
                    public List<String> apply(TaxonomyLevelConfig taxonomyLevelConfig) {
                        List<String> filters = new ArrayList<>();
                        if (parameters.containsKey(taxonomyLevelConfig.getLegacyParameterName())) {
                            for(String value : parameters.get(taxonomyLevelConfig.getLegacyParameterName())) {
                                filters.add(taxonomyLevelConfig.getFilterPrefix() + value + taxonomyLevelConfig.getFilterSuffix());
                            }
                        }
                        return filters;
                    }
                }).toList();
            solrQueryBuilder.addBooleanFilterField(indexName, filters, "OR", excludeTagName);

filtersFlatMap.scala

taxonomyFieldConfig.taxonomyLevelConfigs.flatMap { config =>
  parameters.get(config.legacyParameterName) match {
    case Some(params) => {
      params.map { param => config.prefix + param + config.suffix }
    }
    case None => ()
  }
}.each(builder.addBoleanFilterField(indexName, _, "OR", excludeTagName))