CustomCollectors.java
/*
* Portions of this software was developed by employees of the National Institute
* of Standards and Technology (NIST), an agency of the Federal Government and is
* being made available as a public service. Pursuant to title 17 United States
* Code Section 105, works of NIST employees are not subject to copyright
* protection in the United States. This software may be subject to foreign
* copyright. Permission in the United States and in foreign countries, to the
* extent that NIST may hold copyright, to use, copy, modify, create derivative
* works, and distribute this software and its documentation without fee is hereby
* granted on a non-exclusive basis, provided that this notice and disclaimer
* of warranty appears in all copies.
*
* THE SOFTWARE IS PROVIDED 'AS IS' WITHOUT ANY WARRANTY OF ANY KIND, EITHER
* EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY
* THAT THE SOFTWARE WILL CONFORM TO SPECIFICATIONS, ANY IMPLIED WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND FREEDOM FROM
* INFRINGEMENT, AND ANY WARRANTY THAT THE DOCUMENTATION WILL CONFORM TO THE
* SOFTWARE, OR ANY WARRANTY THAT THE SOFTWARE WILL BE ERROR FREE. IN NO EVENT
* SHALL NIST BE LIABLE FOR ANY DAMAGES, INCLUDING, BUT NOT LIMITED TO, DIRECT,
* INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES, ARISING OUT OF, RESULTING FROM,
* OR IN ANY WAY CONNECTED WITH THIS SOFTWARE, WHETHER OR NOT BASED UPON WARRANTY,
* CONTRACT, TORT, OR OTHERWISE, WHETHER OR NOT INJURY WAS SUSTAINED BY PERSONS OR
* PROPERTY OR OTHERWISE, AND WHETHER OR NOT LOSS WAS SUSTAINED FROM, OR AROSE OUT
* OF THE RESULTS OF, OR USE OF, THE SOFTWARE OR SERVICES PROVIDED HEREUNDER.
*/
package gov.nist.secauto.metaschema.core.util;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import edu.umd.cs.findbugs.annotations.NonNull;
public final class CustomCollectors {
private CustomCollectors() {
// disable
}
@SuppressWarnings("null")
@NonNull
public static <T> Function<T, T> identity() {
return Function.identity();
}
public static Collector<CharSequence, ?, String> joiningWithOxfordComma(@NonNull String conjunction) {
return Collectors.collectingAndThen(Collectors.toList(), withOxfordComma(conjunction));
}
private static Function<List<CharSequence>, String> withOxfordComma(@NonNull String conjunction) {
return list -> {
int size = list.size();
if (size < 2) {
return String.join("", list);
}
if (size == 2) {
return String.join(" " + conjunction + " ", list);
}
// else there are 3 or more
int last = size - 1;
return String.join(", " + conjunction + " ",
String.join(", ", list.subList(0, last)),
list.get(last));
};
}
/**
* Produce a new stream with duplicates removed based on the provided
* {@code keyMapper}. When a duplicate key is encountered, the second item is
* used. The original sequencing is preserved if the input stream is sequential.
*
* @param <V>
* the item value for the streams
* @param <K>
* the key type
* @param stream
* the stream to reduce
* @param keyMapper
* the key function to use to find unique items
* @return a new stream
*/
public static <V, K> Stream<V> distinctByKey(
@NonNull Stream<V> stream,
@NonNull Function<? super V, ? extends K> keyMapper) {
return distinctByKey(stream, keyMapper, (key, value1, value2) -> value2);
}
/**
* Produce a new stream with duplicates removed based on the provided
* {@code keyMapper}. When a duplicate key is encountered, the provided
* {@code duplicateHandler} is used to determine which item to keep. The
* original sequencing is preserved if the input stream is sequential.
*
* @param <V>
* the item value for the streams
* @param <K>
* the key type
* @param stream
* the stream to reduce
* @param keyMapper
* the key function to use to find unique items
* @param duplicateHander
* used to determine which of two duplicates to keep
* @return a new stream
*/
public static <V, K> Stream<V> distinctByKey(
@NonNull Stream<V> stream,
@NonNull Function<? super V, ? extends K> keyMapper,
@NonNull DuplicateHandler<K, V> duplicateHander) {
Map<K, V> uniqueRoles = stream
.collect(toMap(
keyMapper,
identity(),
duplicateHander,
LinkedHashMap::new));
return uniqueRoles.values().stream();
}
@NonNull
public static <T, K, V> Collector<T, ?, Map<K, V>> toMap(
@NonNull Function<? super T, ? extends K> keyMapper,
@NonNull Function<? super T, ? extends V> valueMapper,
@NonNull DuplicateHandler<K, V> duplicateHander) {
return toMap(keyMapper, valueMapper, duplicateHander, HashMap::new);
}
@NonNull
public static <T, K, V, M extends Map<K, V>> Collector<T, ?, M> toMap(
@NonNull Function<? super T, ? extends K> keyMapper,
@NonNull Function<? super T, ? extends V> valueMapper,
@NonNull DuplicateHandler<K, V> duplicateHander,
Supplier<M> supplier) {
return ObjectUtils.notNull(
Collector.of(
supplier,
(map, item) -> {
K key = keyMapper.apply(item);
V value = Objects.requireNonNull(valueMapper.apply(item));
V oldValue = map.get(key);
if (oldValue != null) {
value = duplicateHander.handle(key, oldValue, value);
}
map.put(key, value);
},
(map1, map2) -> {
map2.forEach((key, value) -> {
V oldValue = map1.get(key);
V newValue = value;
if (oldValue != null) {
newValue = duplicateHander.handle(key, oldValue, value);
}
map1.put(key, newValue);
});
return map1;
}));
}
@FunctionalInterface
public interface DuplicateHandler<K, V> {
@NonNull
V handle(K key, @NonNull V value1, V value2);
}
@NonNull
public static <T> BinaryOperator<T> useFirstMapper() {
return (value1, value2) -> value1;
}
@NonNull
public static <T> BinaryOperator<T> useLastMapper() {
return (value1, value2) -> value2;
}
}