CollectionUtil.java

public class CollectionUtil {

	/**
	 * Distinct by multiple fields – distinctByKeys() function
	 * 
	 * <PRE>
	 * List<Record> list = recordsList.stream()
	 * 		.filter(distinctByKeys(Record::getId, Record::getName))
	 * 		.collect(Collectors.toList());
	 * </PRE>
	 * 
	 * @see https://howtodoinjava.com/java8/stream-distinct-by-multiple-fields/
	 * 
	 * @param <T>
	 * @param keyExtractors
	 * @return
	 */
	public static <T> Predicate<T> distinctByKeys(Function<? super T, ?>... keyExtractors) {
		final Map<List<?>, Boolean> seen = new ConcurrentHashMap<>();

		return t -> {
			final List<?> keys = Arrays.stream(keyExtractors).map(ke -> ke.apply(t)).collect(Collectors.toList());

			return seen.putIfAbsent(keys, Boolean.TRUE) == null;
		};
	}

}