com.commercetools.sync.commons.utils.CollectionUtils Maven / Gradle / Ivy
package com.commercetools.sync.commons.utils;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.util.Collection;
import java.util.Collections;
import java.util.Map;
import java.util.Set;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Stream;
import static java.util.stream.Collectors.toMap;
import static java.util.stream.Collectors.toSet;
public final class CollectionUtils {
/**
* Create a new collection which contains only elements which satisfy {@code includeCondition} predicate.
*
* @param collection {@link Collection} to be filtered
* @param includeCondition condition which verifies whether the value should be included to the final result.
* @param type of the collection items.
* @return new filtered stream with items which satisfy {@code includeCondition} predicate. If {@code collection}
* is null or empty - empty stream is returned.
*/
@Nonnull
public static Stream filterCollection(@Nullable final Collection collection,
@Nonnull final Predicate includeCondition) {
return collection == null ? Stream.empty()
: collection.stream()
.filter(includeCondition);
}
/**
* Convert a {@code collection} to a set of values using {@code keyMapper} mapping.
*
* If the collection has duplicate keys - only one will be stored, which one is not defined though.
*
* @param collection {@link Collection} to convert
* @param keyMapper function which converts the collection entry to a key.
* @param type of collection entries
* @param type of Set key
* @return new {@link Set} which consists of items, converted from <T> entries to keys using
* {@code entryToKey} function.
*/
@Nonnull
public static Set collectionToSet(@Nullable final Collection collection,
@Nonnull final Function keyMapper) {
return collection == null ? Collections.emptySet()
: collection.stream()
.map(keyMapper)
.collect(toSet());
}
/**
* Convert a {@code collection} to a map using {@code keyMapper} and {@code valueMapper} mappers.
* If keys are duplicated - only one value is stored, which one - undefined.
*
* @param collection {@link Collection} to convert
* @param keyMapper function which converts the collection entry to a key
* @param valueMapper function which converts the collection entry to a value
* @param type of collection entries
* @param type of Map key
* @param type of Map value
* @return new {@link Map} which consists of key-value pairs, converted from <T> entries
* @see #collectionToMap(Collection, Function)
*/
@Nonnull
public static Map collectionToMap(@Nullable final Collection collection,
@Nonnull final Function keyMapper,
@Nonnull final Function valueMapper) {
return collection == null ? Collections.emptyMap()
: collection.stream()
.collect(toMap(keyMapper, valueMapper, (k1, k2) -> k1)); // ignore duplicates
}
/**
* Same as {@link #collectionToMap(Collection, Function, Function)}, but uses entries themselves as map values.
*
* @param collection {@link Collection} to convert
* @param keyMapper function which converts the collection entry to a key
* @param type of collection entries
* @param type of Map key
* @return new {@link Map} which consists of key-value pairs, converted from <T> entries
* @see #collectionToMap(Collection, Function, Function)
*/
@Nonnull
public static Map collectionToMap(@Nullable final Collection collection,
@Nonnull final Function keyMapper) {
return collectionToMap(collection, keyMapper, value -> value);
}
private CollectionUtils() {
}
}