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Utilities for Java development
There is a newer version: 1.3.8.1
package devutility.internal.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class CollectionUtils {
	/**
	 * If collection does null or empty?
	 * @param collection: Elements collection.
	 * @return boolean
	 */
	public static  boolean isNullOrEmpty(Collection collection) {
		return collection == null || collection.size() == 0;
	}

	/**
	 * If collection does not empty?
	 * @param collection: Elements collection.
	 * @return boolean
	 */
	public static  boolean isNotEmpty(Collection collection) {
		return collection != null && collection.size() > 0;
	}

	/**
	 * Sort by comparator and return the minimum value.
	 * @param collection: Elements collection.
	 * @param comparator: Comparator for sort.
	 * @return {@code E}
	 */
	public static  E min(Collection collection, Comparator comparator) {
		Optional optional = collection.stream().min(comparator);

		if (optional.isPresent()) {
			return optional.get();
		}

		return null;
	}

	/**
	 * Return the minimum integer value.
	 * @param collection: Elements collection.
	 * @return int
	 */
	public static int minInt(Collection collection) {
		Integer value = min(collection, Comparator.comparingInt(i -> i));

		if (value == null) {
			return 0;
		}

		return value;
	}

	/**
	 * Sort by comparator and return the maximum value.
	 * @param collection: Elements collection.
	 * @param comparator: Comparator for sort.
	 * @return {@code E}
	 */
	public static  E max(Collection collection, Comparator comparator) {
		Optional optional = collection.stream().max(comparator);

		if (optional.isPresent()) {
			return optional.get();
		}

		return null;
	}

	/**
	 * Return the maximum integer value.
	 * @param collection: Elements collection.
	 * @return int
	 */
	public static int maxInt(Collection collection) {
		Integer value = max(collection, Comparator.comparingInt(i -> i));

		if (value == null) {
			return 0;
		}

		return value;
	}

	/**
	 * Calculate elements that meet predicate command.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @return long
	 */
	public static  long count(Collection collection, Predicate predicate) {
		return collection.stream().filter(predicate).count();
	}

	/**
	 * Execute predicate and check whether any object exist?
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @return boolean
	 */
	public static  boolean exist(Collection collection, Predicate predicate) {
		return count(collection, predicate) > 0;
	}

	/**
	 * Find element by predicate command and return optional object.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @return {@code Optional}
	 */
	public static  Optional findOptional(Collection collection, Predicate predicate) {
		return collection.stream().filter(predicate).findAny();
	}

	/**
	 * Find element by predicate command and return it.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @return {@code E}
	 */
	public static  E find(Collection collection, Predicate predicate) {
		Optional optional = findOptional(collection, predicate);

		if (optional.isPresent()) {
			return optional.get();
		}

		return null;
	}

	/**
	 * Parallel find element by predicate command and return optional object.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @return {@code Optional}
	 */
	public static  Optional parallelFindOptional(Collection collection, Predicate predicate) {
		return collection.stream().parallel().filter(predicate).findAny();
	}

	/**
	 * Parallel find element by predicate command and return it.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @return {@code E}
	 */
	public static  E parallelFind(Collection collection, Predicate predicate) {
		Optional optional = parallelFindOptional(collection, predicate);

		if (optional.isPresent()) {
			return optional.get();
		}

		return null;
	}

	/**
	 * Query elements by predicate command and return a stream.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @return {@code Stream}
	 */
	public static  Stream query(Collection collection, Predicate predicate) {
		return collection.stream().filter(predicate);
	}

	/**
	 * Parallel query elements by predicate command and return a stream.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @return {@code Stream}
	 */
	public static  Stream parallelQuery(Collection collection, Predicate predicate) {
		return collection.stream().parallel().filter(predicate);
	}

	/**
	 * Query elements by predicate command and return a list.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @return {@code List}
	 */
	public static  List list(Collection collection, Predicate predicate) {
		return query(collection, predicate).collect(Collectors.toList());
	}

	/**
	 * Parallel query elements by predicate command and return a list.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @return {@code List}
	 */
	public static  List parallelList(Collection collection, Predicate predicate) {
		return parallelQuery(collection, predicate).collect(Collectors.toList());
	}

	/**
	 * Map some fields and return a stream.
	 * @param collection: Elements collection.
	 * @param mapper: Fields mapper.
	 * @return {@code Stream}
	 */
	public static  Stream map(Collection collection, Function mapper) {
		return collection.stream().map(mapper);
	}

	/**
	 * Map some fields and return a list.
	 * @param collection: Elements collection.
	 * @param mapper: Fields mapper.
	 * @return {@code List}
	 */
	public static  List mapToList(Collection collection, Function mapper) {
		return map(collection, mapper).collect(Collectors.toList());
	}

	/**
	 * Map some fields and return a Set.
	 * @param collection: Elements collection.
	 * @param mapper: Fields mapper.
	 * @return {@code Set}
	 */
	public static  Set mapToSet(Collection collection, Function mapper) {
		return map(collection, mapper).collect(Collectors.toSet());
	}

	/**
	 * Query elements by predicate command, map some fields and return a stream.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @param mapper: Fields mapper.
	 * @return {@code Stream}
	 */
	public static  Stream map(Collection collection, Predicate predicate, Function mapper) {
		return query(collection, predicate).map(mapper);
	}

	/**
	 * Query elements by predicate command, map some fields and return a list.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @param mapper: Fields mapper.
	 * @return {@code List}
	 */
	public static  List mapToList(Collection collection, Predicate predicate, Function mapper) {
		return map(collection, predicate, mapper).collect(Collectors.toList());
	}

	/**
	 * Query elements by predicate command, map some fields and return a Set.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @param mapper: Fields mapper.
	 * @return {@code Set}
	 */
	public static  Set mapToSet(Collection collection, Predicate predicate, Function mapper) {
		return map(collection, predicate, mapper).collect(Collectors.toSet());
	}

	/**
	 * Parallel map some fields and return a stream.
	 * @param collection: Elements collection.
	 * @param mapper: Fields mapper.
	 * @return {@code Stream}
	 */
	public static  Stream parallelMap(Collection collection, Function mapper) {
		return collection.stream().parallel().map(mapper);
	}

	/**
	 * Parallel map some fields and return a list.
	 * @param collection: Elements collection.
	 * @param mapper: Fields mapper.
	 * @return {@code List}
	 */
	public static  List parallelMapToList(Collection collection, Function mapper) {
		return parallelMap(collection, mapper).collect(Collectors.toList());
	}

	/**
	 * Parallel query elements by predicate command, map some fields and return a
	 * stream.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @param mapper: Fields mapper.
	 * @return {@code Stream}
	 */
	public static  Stream parallelMap(Collection collection, Predicate predicate, Function mapper) {
		return collection.stream().parallel().filter(predicate).map(mapper);
	}

	/**
	 * Parallel query elements by predicate command, map some fields and return a
	 * list.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @param mapper: Fields mapper.
	 * @return {@code List}
	 */
	public static  List parallelMapToList(Collection collection, Predicate predicate, Function mapper) {
		return parallelMap(collection, predicate, mapper).collect(Collectors.toList());
	}

	/**
	 * Map some fields, remove repeated items and return a stream.
	 * @param collection: Elements collection.
	 * @param mapper: Fields mapper.
	 * @return {@code Stream}
	 */
	public static  Stream mapAndDistinct(Collection collection, Function mapper) {
		return map(collection, mapper).distinct();
	}

	/**
	 * Map some fields, remove repeated items and return a list.
	 * @param collection: Elements collection.
	 * @param mapper: Fields mapper.
	 * @return {@code List}
	 */
	public static  List mapAndDistinctToList(Collection collection, Function mapper) {
		return mapAndDistinct(collection, mapper).collect(Collectors.toList());
	}

	/**
	 * Query elements by predicate command, map some fields, remove repeated items
	 * and return a stream.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @param mapper: Fields mapper.
	 * @return {@code Stream}
	 */
	public static  Stream mapAndDistinct(Collection collection, Predicate predicate, Function mapper) {
		return map(collection, predicate, mapper).distinct();
	}

	/**
	 * Query elements by predicate command, map some fields, remove repeated items
	 * and return a list.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @param mapper: Fields mapper.
	 * @return {@code List}
	 */
	public static  List mapAndDistinctToList(Collection collection, Predicate predicate, Function mapper) {
		return mapAndDistinct(collection, predicate, mapper).collect(Collectors.toList());
	}

	/**
	 * Map some fields (for each item, one field has an collection of values) and
	 * return a list.
	 * @param collection: Elements collection.
	 * @param mapper: Fields mapper.
	 * @return {@code List}
	 */
	public static  List mapManyToList(Collection collection, Function> mapper) {
		List list = new LinkedList<>();

		map(collection, mapper).forEach(i -> {
			list.addAll(i.collect(Collectors.toList()));
		});

		return list;
	}

	/**
	 * Group collection by classifier to map and return it.
	 * @param collection: Elements collection.
	 * @param classifier: Classifier for group.
	 * @return {@code Map>}
	 */
	public static  Map> groupToMap(Collection collection, Function classifier) {
		return collection.stream().collect(Collectors.groupingBy(classifier));
	}

	/**
	 * Parallel group collection by classifier to map and return it.
	 * @param collection: Elements collection.
	 * @param classifier: Classifier for group.
	 * @return {@code Map>}
	 */
	public static  Map> parallelGroupToMap(Collection collection, Function classifier) {
		return collection.stream().parallel().collect(Collectors.groupingBy(classifier));
	}

	/**
	 * Query elements by predicate command, group collection by classifier to map
	 * and return it.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @param classifier: Classifier for group.
	 * @return {@code Map>}
	 */
	public static  Map> groupToMap(Collection collection, Predicate predicate, Function classifier) {
		return query(collection, predicate).collect(Collectors.groupingBy(classifier));
	}

	/**
	 * Parallel group elements by predicate command, group collection by classifier
	 * to map and return it.
	 * @param collection: Elements collection.
	 * @param predicate: Predicate command.
	 * @param classifier: Classifier for group.
	 * @return {@code Map>}
	 */
	public static  Map> parallelGroupToMap(Collection collection, Predicate predicate, Function classifier) {
		return parallelQuery(collection, predicate).collect(Collectors.groupingBy(classifier));
	}

	/**
	 * Paging collection with specified page index and page size.
	 * @param collection: Elements collection.
	 * @param pageIndex: Page index.
	 * @param pageSize: Page size.
	 * @return {@code List}
	 */
	public static  List paging(Collection collection, int pageIndex, int pageSize) {
		if (isNullOrEmpty(collection) || pageIndex < 1) {
			return new ArrayList<>();
		}

		int skip = (pageIndex - 1) * pageSize;

		if (skip < 0 || skip >= collection.size()) {
			return new ArrayList<>();
		}

		return collection.stream().skip(skip).limit(pageSize).collect(Collectors.toList());
	}

	/**
	 * Get the toppest count elements.
	 * @param collection: Elements collection.
	 * @param count: Count number.
	 * @return {@code List}
	 */
	public static  List top(Collection collection, int count) {
		if (isNullOrEmpty(collection) || count < 1) {
			return new ArrayList<>();
		}

		return collection.stream().limit(count).collect(Collectors.toList());
	}
}