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Some utilities for Java development
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.BinaryOperator;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
import java.util.stream.Collectors;
import java.util.stream.Stream;
/**
*
* CollectionUtils
*
* @author: Aldwin Su
* @version: 2019-06-22 10:29:36
*/
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());
}
/**
* Map some fields, remove repeated items and return a set.
* @param collection Elements collection.
* @param mapper Fields mapper.
* @return {@code Set}
*/
public static Set mapAndDistinctToSet(Collection collection, Function mapper) {
return mapAndDistinct(collection, mapper).collect(Collectors.toSet());
}
/**
* 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());
}
/**
* Query elements by predicate command, map some fields, remove repeated items and return a set.
* @param collection Elements collection.
* @param predicate Predicate command.
* @param mapper Fields mapper.
* @return {@code Set}
*/
public static Set mapAndDistinctToSet(Collection collection, Predicate predicate, Function mapper) {
return mapAndDistinct(collection, predicate, mapper).collect(Collectors.toSet());
}
/**
* 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));
}
/**
* Convert collection to Map.
* @param the type of the input elements
* @param the output type of the key mapping function
* @param the output type of the value mapping function
* @param collection Elements collection.
* @param keyMapper a mapping function to produce keys.
* @param valueMapper a mapping function to produce values.
* @return {@code Map}
*/
public static Map toMap(Collection collection, Function keyMapper, Function valueMapper) {
return collection.stream().collect(Collectors.toMap(keyMapper, valueMapper));
}
/**
* Convert collection to Map.
* @param the type of the input elements
* @param the output type of the key mapping function
* @param the output type of the value mapping function
* @param collection Elements collection.
* @param keyMapper a mapping function to produce keys.
* @param valueMapper a mapping function to produce values.
* @param mergeFunction a merge function, selector function.
* @param mapSupplier a function which returns a new, empty Map into which the results will be inserted
* @return {@code Map}
*/
public static > Map toMap(Collection collection, Function keyMapper, Function valueMapper, BinaryOperator mergeFunction, Supplier mapSupplier) {
return collection.stream().collect(Collectors.toMap(keyMapper, valueMapper, mergeFunction, mapSupplier));
}
/**
* Parallel convert collection to Map.
* @param the type of the input elements
* @param the output type of the key mapping function
* @param the output type of the value mapping function
* @param collection Elements collection.
* @param keyMapper a mapping function to produce keys.
* @param valueMapper a mapping function to produce values.
* @return {@code Map}
*/
public static Map parallelToMap(Collection collection, Function keyMapper, Function valueMapper) {
return collection.stream().parallel().collect(Collectors.toMap(keyMapper, valueMapper));
}
/**
* Parallel convert collection to Map.
* @param the type of the input elements
* @param the output type of the key mapping function
* @param the output type of the value mapping function
* @param collection Elements collection.
* @param keyMapper a mapping function to produce keys.
* @param valueMapper a mapping function to produce values.
* @param mergeFunction a merge function, selector function.
* @return {@code Map}
*/
public static Map parallelToMap(Collection collection, Function keyMapper, Function valueMapper, BinaryOperator mergeFunction) {
return collection.stream().parallel().collect(Collectors.toMap(keyMapper, valueMapper, mergeFunction));
}
/**
* Convert collection to Map.
* @param the type of the input elements
* @param the output type of the key mapping function
* @param the output type of the value mapping function
* @param collection Elements collection.
* @param predicate Predicate command.
* @param keyMapper a mapping function to produce keys.
* @param valueMapper a mapping function to produce values.
* @return {@code Map}
*/
public static Map toMap(Collection collection, Predicate predicate, Function keyMapper, Function valueMapper) {
return query(collection, predicate).collect(Collectors.toMap(keyMapper, valueMapper));
}
/**
* Convert collection to Map.
* @param the type of the input elements
* @param the output type of the key mapping function
* @param the output type of the value mapping function
* @param collection Elements collection.
* @param predicate Predicate command.
* @param keyMapper a mapping function to produce keys.
* @param valueMapper a mapping function to produce values.
* @param mergeFunction a merge function, selector function.
* @return {@code Map}
*/
public static Map toMap(Collection collection, Predicate predicate, Function keyMapper, Function valueMapper, BinaryOperator mergeFunction) {
return query(collection, predicate).collect(Collectors.toMap(keyMapper, valueMapper, mergeFunction));
}
/**
* Parallel convert collection to Map.
* @param the type of the input elements
* @param the output type of the key mapping function
* @param the output type of the value mapping function
* @param collection Elements collection.
* @param predicate Predicate command.
* @param keyMapper a mapping function to produce keys.
* @param valueMapper a mapping function to produce values.
* @return {@code Map}
*/
public static Map parallelToMap(Collection collection, Predicate predicate, Function keyMapper, Function valueMapper) {
return parallelQuery(collection, predicate).collect(Collectors.toMap(keyMapper, valueMapper));
}
/**
* Parallel convert collection to Map.
* @param the type of the input elements
* @param the output type of the key mapping function
* @param the output type of the value mapping function
* @param collection Elements collection.
* @param predicate Predicate command.
* @param keyMapper a mapping function to produce keys.
* @param valueMapper a mapping function to produce values.
* @param mergeFunction a merge function, selector function.
* @return {@code Map}
*/
public static Map parallelToMap(Collection collection, Predicate predicate, Function keyMapper, Function valueMapper, BinaryOperator mergeFunction) {
return parallelQuery(collection, predicate).collect(Collectors.toMap(keyMapper, valueMapper));
}
/**
* 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());
}
}