<dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-collections4</artifactId> <version>4.4</version> </dependency> import org.apache.commons.collections4.ListUtils; List<String> list1 = Arrays.asList("A", "B", "C"); List<String> list2 = Arrays.asList("D", "E", "F"); List<String> mergedList = ListUtils.union(list1, list2); List<String> intersection = ListUtils.intersection(list1, list2); List<String> combinedList = ListUtils.sum(list1, list2); import org.apache.commons.collections4.MapUtils; Map<String, Integer> map = new HashMap<>(); map.put("A", 1); map.put("B", 2); map.put("C", 3); boolean isEmpty = MapUtils.isEmpty(map); int defaultValue = MapUtils.getIntValue(map, "D"); Map<Integer, String> reversedMap = MapUtils.invertMap(map);