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Misc utilities to hide most common boilerplate code. Requires jdk8 at least
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/**
* Copyright © 2016
* Maksim Lozbin
* Oleksii Ihnachuk
*
* This work is free. You can redistribute it and/or modify it under the
* terms of the Do What The Fuck You Want To Public License, Version 2,
* as published by Sam Hocevar. See http://www.wtfpl.net/ for more details.
*/
package com.github.nginate.commons.lang;
import lombok.NonNull;
import lombok.experimental.UtilityClass;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.util.*;
import java.util.function.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import static java.util.function.Function.identity;
/**
* Functional utilities to operate over java collections
*
* @since 1.0
*/
@SuppressWarnings({"WeakerAccess", "OptionalGetWithoutIsPresent"})
@UtilityClass
public class NCollections {
/**
* Return first element of collection or null if collection is null or is empty
*
* @param collection generic collection
* @param type of collection
* @return first element ot null
*/
@Nullable
public static T getFirst(@NonNull Collection collection) {
return !collection.isEmpty() ? collection.iterator().next() : null;
}
/**
* Return first element of collection, wrapping it in {@code Optional}. If collection is null or is empty,
* the result of operation will be empty optional.
*
* @param collection generic collection
* @param type of collection
* @return optional of first element if present ot empty
*/
@Nonnull
public static Optional getFirstOptional(@NonNull Collection collection) {
return Optional.ofNullable(getFirst(collection));
}
/**
* Return first element of collection. Will throw NoSuchElementException if collection is null or empty
*
* @param collection generic collection
* @param type of collection
* @return the non-null value of first element
* @throws NoSuchElementException if there is no value present
* @see Optional#isPresent()
*/
@Nonnull
public static T requireFirst(@NonNull Collection collection) {
return getFirstOptional(collection).get();
}
/**
* Transform collection of one element into this one element (retrieve it). Will return null if collection is null
* or empty
*
* @param collection generic collection
* @param type of collection
* @return first and single existing element of collection or null
* @throws IllegalArgumentException if collection has more than one elements
* @see NCollections#getFirst(Collection)
*/
@Nullable
public static T getSingle(@NonNull Collection collection) {
if (collection.size() > 1) {
throw new IllegalArgumentException("Wrong collection size " + collection.size());
}
return getFirst(collection);
}
/**
* Transform collection of one element into {@code Optional} of this element. Will return {@code Optional.empty()}
* if collection is null or empty
*
* @param collection generic collection
* @param type of collection
* @return optional of first and single existing element of collection or {@code Optional.empty()}
* @throws IllegalArgumentException if collection has more than one elements
* @see NCollections#getSingle(Collection)
*/
@Nonnull
public static Optional getSingleOptional(@NonNull Collection collection) {
return Optional.ofNullable(getSingle(collection));
}
/**
* Return non-null element from a collection, containing only one element.
*
* @param collection generic collection
* @param type of collection
* @return single non-null element from a collection
* @throws IllegalArgumentException if collection has more than one elements
* @throws NoSuchElementException if there is no value present
*/
@Nonnull
public static T requireSingle(@NonNull Collection collection) {
return getSingleOptional(collection).get();
}
/**
* Convert collection to an array of same type. Will return null if original collection is null
*
* @param original generic collection
* @param generator array provider
* @param type of elements
* @return array, containing all elements of collection, or null if source is null
* @see NCollections#mapToArray(Collection, IntFunction, Function)
*/
@Nullable
public static T[] mapToArray(@Nullable Collection original, @NonNull IntFunction generator) {
return mapToArray(original, generator, identity());
}
/**
* Convert collection of one type to an array of other type using provided mapping function. Will return null if
* original collection is null
*
* @param original source collection
* @param generator array provider
* @param mapper function to convert source element type to dest element type
* @param destination type
* @param source type
* @return array, containing all elements of collection, or null if source is null
*/
@Nullable
public static T[] mapToArray(@Nullable Collection original,
@NonNull IntFunction generator, @NonNull Function mapper) {
return original != null ? original.stream().map(mapper).toArray(generator) : null;
}
/**
* Convert source collection of type O to a list of type T using provided mapping function. Will return null if
* source collection is null
*
* @param original source collection
* @param mapper function to convert source element type to dest element type
* @param destination type
* @param source type
* @return list, containing all elements of collection, or null if source is null
*/
@Nullable
public static List mapToList(@Nullable Collection original, @NonNull Function mapper) {
return original != null ? original.stream().map(mapper).collect(Collectors.toList()) : null;
}
/**
* Convert source collection to a map, using two provided functions to extract keys and values from source elements.
* Will return null if source is null
*
* @param original source collection
* @param keyMapper function to map map key from source element
* @param valueMapper function to map map value from source element
* @param key type
* @param value type
* @param source type
* @return map, containing mapped source elements, or null if source is null
*/
@Nullable
public static Map mapToMap(@Nullable Collection original, @NonNull Function keyMapper,
@NonNull Function valueMapper) {
return original != null ? original.stream().collect(Collectors.toMap(keyMapper, valueMapper)) : null;
}
/**
* Convert source collection to a map, using provided function to extract keys from source elements.
* Will return null if source is null
*
* @param original source collection
* @param keyMapper function to map map key from source element
* @param key type
* @param value and source type
* @return map, containing all source elements as values, or null if source is null
*/
@Nullable
public static Map mapToMap(@Nullable Collection original, Function keyMapper) {
return mapToMap(original, keyMapper, identity());
}
/**
* Get a copy of source collection without elements that do not fit to a predicate conditions
*
* @param original source collection
* @param predicate source element predicate
* @param source type
* @return collection copy with matched elements
*/
@Nonnull
public static List filter(@NonNull @Nonnull Collection original,
@NonNull @Nonnull Predicate predicate) {
return original.stream().filter(predicate).collect(Collectors.toList());
}
/**
* Get any element from provided collection that matches predicate conditions
*
* @param original source collection
* @param predicate element predicate
* @param source type
* @return any matched element
* @see Stream#findAny()
*/
@Nonnull
public static Optional findAny(@NonNull @Nonnull Collection original, @Nonnull Predicate predicate) {
return original.stream().filter(predicate).findAny();
}
/**
* Execute provided action over each element of source collection if it is not null, skip otherwise
*
* @param collection source collection
* @param action element consumer
* @param source type
*/
public static void forEach(@Nullable Collection collection, @Nonnull Consumer action) {
if (collection != null) {
collection.forEach(action);
}
}
/**
* Convert map to a list, using provided function to combine map entry to a destination list type
*
* @param original source map
* @param mapper function to combine amd convert map entry to a required type
* @param key type
* @param value type
* @param destination type
* @return list, containing mapped entries, or null if source is null
*/
@Nullable
public static List mapToList(@Nullable Map original,
@NonNull BiFunction mapper) {
if (original == null) {
return null;
}
return mapToList(original.entrySet(), entry -> mapper.apply(entry.getKey(), entry.getValue()));
}
/**
* Convert map to an array, using provided function to combine map entry to a destination array type. Will return
* null if source is null
*
* @param original source map
* @param generator array provider
* @param mapper function to combine amd convert map entry to a required type
* @param map key type
* @param map value type
* @param array type
* @return array, containing mapped entries, or null if source is null
*/
@Nullable
public static T[] mapToArray(@Nullable Map original,
@NonNull IntFunction generator,
@NonNull BiFunction mapper) {
if (original == null) {
return null;
}
return mapToArray(original.entrySet(), generator, entry -> mapper.apply(entry.getKey(), entry.getValue()));
}
}
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