public static <T> Collector<? super T, ?, T> reducing(BinaryOperator<T> op) {
Supplier<SettableValue<T>> supplier = SettableValue::new;
BiConsumer<SettableValue<T>, T> accumulator = (box, ele) -> box.set(ele);
BinaryOperator<SettableValue<T>> combiner = SettableValue::merge;
Function<SettableValue<T>, T> finisher = SettableValue::get;
return Collector.of(supplier, accumulator, combiner, finisher);
}
/**
* of the summary of the MonetaryAmount
*
* @param currencyUnit the target {@link javax.money.CurrencyUnit}
* @return the MonetarySummaryStatistics
*/
public static Collector<MonetaryAmount, MonetarySummaryStatistics, MonetarySummaryStatistics>
summarizingMonetary(CurrencyUnit currencyUnit) {
Supplier<MonetarySummaryStatistics> supplier =
() -> new DefaultMonetarySummaryStatistics(currencyUnit);
return Collector.of(
supplier, MonetarySummaryStatistics::accept, MonetarySummaryStatistics::combine);
}
/** Collector to create a Guava ImmutableList. */
public static <T> Collector<T, ?, ImmutableList<T>> toImmutableList() {
return Collector.of(
ImmutableList.Builder<T>::new,
ImmutableList.Builder::add,
(l, r) -> l.addAll(r.build()),
ImmutableList.Builder::build);
}
/**
* of MonetaryAmount group by MonetarySummary
*
* @return the MonetarySummaryStatistics
*/
public static Collector<
MonetaryAmount, GroupMonetarySummaryStatistics, GroupMonetarySummaryStatistics>
groupBySummarizingMonetary() {
return Collector.of(
GroupMonetarySummaryStatistics::new,
GroupMonetarySummaryStatistics::accept,
GroupMonetarySummaryStatistics::combine);
}
/**
* of the summary of the MonetaryAmount
*
* @param currencyUnit the target {@link javax.money.CurrencyUnit}
* @return the MonetarySummaryStatistics
*/
public static Collector<MonetaryAmount, MonetarySummaryStatistics, MonetarySummaryStatistics>
summarizingMonetary(CurrencyUnit currencyUnit, ExchangeRateProvider provider) {
Supplier<MonetarySummaryStatistics> supplier =
() -> new ExchangeRateMonetarySummaryStatistics(currencyUnit, provider);
return Collector.of(
supplier, MonetarySummaryStatistics::accept, MonetarySummaryStatistics::combine);
}
/** Collector to create a Guava ImmutableSet. */
public static <T> Collector<T, ?, ImmutableSet<T>> toImmutableSet() {
return Collector.of(
ImmutableSet.Builder<T>::new,
ImmutableSet.Builder::add,
(l, r) -> l.addAll(r.build()),
ImmutableSet.Builder::build,
UNORDERED);
}
public static <T> Collector<T, ?, ObservableList<T>> toObservableList() {
return Collector.of(
(Supplier<ObservableList<T>>) FXCollections::observableArrayList,
List::add,
(left, right) -> {
left.addAll(right);
return left;
});
}
public static <T extends JsonElement> Collector<T, JsonArray, JsonArray> toJsonArray() {
return Collector.of(
JsonArray::new,
(array, element) -> array.add(element),
(one, other) -> {
one.addAll(other);
return one;
},
Characteristics.IDENTITY_FINISH);
}
/**
* Returns a {@link java.util.stream.Collector} which may be used in conjunction with {@link
* java.util.stream.Stream#collect(java.util.stream.Collector)} to obtain a {@link
* javaslang.collection.Tree}.
*
* @param <T> Component type of the Tree.
* @return A javaslang.collection.Tree Collector.
*/
static <T> Collector<T, ArrayList<T>, Tree<T>> collector() {
final Supplier<ArrayList<T>> supplier = ArrayList::new;
final BiConsumer<ArrayList<T>, T> accumulator = ArrayList::add;
final BinaryOperator<ArrayList<T>> combiner =
(left, right) -> {
left.addAll(right);
return left;
};
final Function<ArrayList<T>, Tree<T>> finisher = Tree::ofAll;
return Collector.of(supplier, accumulator, combiner, finisher);
}
/**
* Returns a {@link java.util.stream.Collector} which may be used in conjunction with {@link
* java.util.stream.Stream#collect(java.util.stream.Collector)} to obtain a {@link
* javaslang.collection.HashMap}.
*
* @param <K> The key type
* @param <V> The value type
* @return A {@link javaslang.collection.HashMap} Collector.
*/
public static <K, V> Collector<Tuple2<K, V>, ArrayList<Tuple2<K, V>>, HashMap<K, V>> collector() {
final Supplier<ArrayList<Tuple2<K, V>>> supplier = ArrayList::new;
final BiConsumer<ArrayList<Tuple2<K, V>>, Tuple2<K, V>> accumulator = ArrayList::add;
final BinaryOperator<ArrayList<Tuple2<K, V>>> combiner =
(left, right) -> {
left.addAll(right);
return left;
};
final Function<ArrayList<Tuple2<K, V>>, HashMap<K, V>> finisher = HashMap::ofAll;
return Collector.of(supplier, accumulator, combiner, finisher);
}
/**
* Returns a {@link java.util.stream.Collector} which may be used in conjunction with {@link
* java.util.stream.Stream#collect(java.util.stream.Collector)} to obtain a {@link
* javaslang.collection.TreeMap}.
*
* @param <K> The key type
* @param <V> The value type
* @return A {@link javaslang.collection.TreeMap} Collector.
*/
public static <K, V> Collector<Tuple2<K, V>, ArrayList<Tuple2<K, V>>, TreeMap<K, V>> collector() {
final Supplier<ArrayList<Tuple2<K, V>>> supplier = ArrayList::new;
final BiConsumer<ArrayList<Tuple2<K, V>>, Tuple2<K, V>> accumulator = ArrayList::add;
final BinaryOperator<ArrayList<Tuple2<K, V>>> combiner =
(left, right) -> {
left.addAll(right);
return left;
};
final Comparator<? super K> comparator = naturalComparator();
final Function<ArrayList<Tuple2<K, V>>, TreeMap<K, V>> finisher =
list -> TreeMap.ofEntries(comparator, list);
return Collector.of(supplier, accumulator, combiner, finisher);
}
default <R> R collect(
Supplier<R> supplier, BiConsumer<R, ? super U> accumulator, BiConsumer<R, R> combiner) {
return (R)
this.run(
(Collector)
Collector.of(
supplier,
accumulator,
(a, b) -> {
combiner.accept(a, b);
return a;
}));
}
/**
* Returns a {@link Collector} which may be used in conjunction with {@link
* java.util.stream.Stream#collect(Collector)} to obtain a {@link TreeMap}.
*
* @param <K> The key type
* @param <V> The value type
* @param keyComparator A key comparator
* @return A {@link TreeMap} Collector.
*/
public static <K, V> Collector<Tuple2<K, V>, ArrayList<Tuple2<K, V>>, TreeMap<K, V>> collector(
Comparator<? super K> keyComparator) {
Objects.requireNonNull(keyComparator, "keyComparator is null");
final Supplier<ArrayList<Tuple2<K, V>>> supplier = ArrayList::new;
final BiConsumer<ArrayList<Tuple2<K, V>>, Tuple2<K, V>> accumulator = ArrayList::add;
final BinaryOperator<ArrayList<Tuple2<K, V>>> combiner =
(left, right) -> {
left.addAll(right);
return left;
};
final Function<ArrayList<Tuple2<K, V>>, TreeMap<K, V>> finisher =
list -> ofEntries(keyComparator, list);
return Collector.of(supplier, accumulator, combiner, finisher);
}
private static void testCollect() {
System.out.println();
System.out.println("Test distinct start");
// ******** Work with numbers
Collection<Integer> numbers = Arrays.asList(1, 2, 3, 4);
// Get sum of all odd numbers
long sumOdd = numbers.stream().collect(Collectors.summingInt(((p) -> p % 2 == 1 ? p : 0)));
System.out.println("sumOdd = " + sumOdd); // print sumEven = 4
// Subtract 1 to every element and get average
double average = numbers.stream().collect(Collectors.averagingInt((p) -> p - 1));
System.out.println("average = " + average); // print average = 1.5
// Add 3 to every element and get statisics
IntSummaryStatistics statistics =
numbers.stream().collect(Collectors.summarizingInt((p) -> p + 3));
System.out.println(
"statistics = "
+ statistics); // print statistics = IntSummaryStatistics{count=4, sum=22, min=4,
// average=5.500000, max=7}
// Get sum all even number using IntSummaryStatistics
long sumEven =
numbers.stream().collect(Collectors.summarizingInt((p) -> p % 2 == 0 ? p : 0)).getSum();
System.out.println("sumEven = " + sumEven); // print sumEven = 6
// Split all number to odd and even
Map<Boolean, List<Integer>> parts =
numbers.stream().collect(Collectors.partitioningBy((p) -> p % 2 == 0));
System.out.println("parts = " + parts); // print parts = {false=[1, 3], true=[2, 4]}
// ******** Work with strings
Collection<String> strings = Arrays.asList("a1", "b2", "c3", "a1");
// Get list of string without duplicate
List<String> distinct = strings.stream().distinct().collect(Collectors.toList());
System.out.println("distinct = " + distinct); // print distinct = [a1, b2, c3]
// Get array of string without duplicate
String[] array = strings.stream().distinct().map(String::toUpperCase).toArray(String[]::new);
System.out.println("array = " + Arrays.asList(array)); // print array = [A1, B2, C3]
// Join all element to one string using template: "<b> v1 : v2 : ... vN </b>"
String join = strings.stream().collect(Collectors.joining(" : ", "<b> ", " </b>"));
System.out.println("join = " + join); // print <b> a1 : b2 : c3 : a1 </b>
// Transform to map, when first char is key, second char - value
Map<String, String> map =
strings
.stream()
.distinct()
.collect(Collectors.toMap((p) -> p.substring(0, 1), (p) -> p.substring(1, 2)));
System.out.println("map = " + map); // print map = {a=1, b=2, c=3}
// Transform to map, with grouping by first char
Map<String, List<String>> groups =
strings.stream().collect(Collectors.groupingBy((p) -> p.substring(0, 1)));
System.out.println("groups = " + groups); // print groups = {a=[a1, a1], b=[b2], c=[c3]}
// Transform to map, with grouping by first char and value is join second chars
Map<String, String> groupJoin =
strings
.stream()
.collect(
Collectors.groupingBy(
(p) -> p.substring(0, 1),
Collectors.mapping((p) -> p.substring(1, 2), Collectors.joining(":"))));
System.out.println(
"groupJoin = " + groupJoin); // print groupJoin = groupJoin = {a=1/1, b=2, c=3}
// Create custom Collector, that join string using StringBuilder
Collector<String, StringBuilder, String> stringBuilderCollector =
Collector.of(
StringBuilder::new, // method accumulator's initialization
(b, s) -> b.append(s).append(" , "), // method that working with every element
(b1, b2) -> b1.append(b2).append(" , "), // method that join to accumulator's
StringBuilder::toString // method that finished working
);
String joinBuilder = strings.stream().collect(stringBuilderCollector);
System.out.println("joinBuilder = " + joinBuilder); // print joinBuilder = a1 , b2 , c3 , a1 ,
// Analog Collector using JDK7-
StringBuilder b = new StringBuilder(); // method accumulator's initialization
for (String s : strings) {
b.append(s).append(" , "); // method that working with every element
}
String joinBuilderOld = b.toString(); // method that finished working
System.out.println(
"joinBuilderOld = " + joinBuilderOld); // print joinBuilderOld = a1 , b2 , c3 , a1 ,
}
private Collector<JsonNode, ArrayNode, ArrayNode> toArrayNode() {
return Collector.of(() -> mapper().createArrayNode(), ArrayNode::add, ArrayNode::addAll);
}