// add fields on index public void addDocument(String... fields) { for (int i = 0; i < fields.length; i++) { final DataType type = schema.getType(i); String field = fields[i]; final Map<String, Set<Integer>> stringSetMap = this.fields.get(i); if (type == DataType.DateYear) { // reformat field value for date year field = field.split("-")[0]; } Set<Integer> integers = stringSetMap.get(field); if (integers == null) { integers = new TreeSet<>(); } integers.add(docPosition); stringSetMap.put(field, integers); } docPosition++; }