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8205461: Create Collector which merges results of two other collectors

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Reviewed-by: briangoetz, smarks, plevart
This commit is contained in:
Tagir Valeev 2018-09-25 14:23:37 +02:00 committed by Peter Levart
parent dd4961b5aa
commit 7c9ab50d06
2 changed files with 161 additions and 4 deletions
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98
src/java.base/share/classes/java/util/stream/Collectors.java
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2012, 2017, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2012, 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -1884,6 +1884,102 @@ public final class Collectors {
(l, r) -> { l.combine(r); return l; }, CH_ID);
}
/**
* Returns a {@code Collector} that is a composite of two downstream collectors.
* Every element passed to the resulting collector is processed by both downstream
* collectors, then their results are merged using the specified merge function
* into the final result.
*
* <p>The resulting collector functions do the following:
*
* <ul>
* <li>supplier: creates a result container that contains result containers
* obtained by calling each collector's supplier
* <li>accumulator: calls each collector's accumulator with its result container
* and the input element
* <li>combiner: calls each collector's combiner with two result containers
* <li>finisher: calls each collector's finisher with its result container,
* then calls the supplied merger and returns its result.
* </ul>
*
* <p>The resulting collector is {@link Collector.Characteristics#UNORDERED} if both downstream
* collectors are unordered and {@link Collector.Characteristics#CONCURRENT} if both downstream
* collectors are concurrent.
*
* @param <T> the type of the input elements
* @param <R1> the result type of the first collector
* @param <R2> the result type of the second collector
* @param <R> the final result type
* @param downstream1 the first downstream collector
* @param downstream2 the second downstream collector
* @param merger the function which merges two results into the single one
* @return a {@code Collector} which aggregates the results of two supplied collectors.
* @since 12
*/
public static <T, R1, R2, R>
Collector<T, ?, R> teeing(Collector<? super T, ?, R1> downstream1,
Collector<? super T, ?, R2> downstream2,
BiFunction<? super R1, ? super R2, R> merger) {
return teeing0(downstream1, downstream2, merger);
}
private static <T, A1, A2, R1, R2, R>
Collector<T, ?, R> teeing0(Collector<? super T, A1, R1> downstream1,
Collector<? super T, A2, R2> downstream2,
BiFunction<? super R1, ? super R2, R> merger) {
Objects.requireNonNull(downstream1, "downstream1");
Objects.requireNonNull(downstream2, "downstream2");
Objects.requireNonNull(merger, "merger");
Supplier<A1> c1Supplier = Objects.requireNonNull(downstream1.supplier(), "downstream1 supplier");
Supplier<A2> c2Supplier = Objects.requireNonNull(downstream2.supplier(), "downstream2 supplier");
BiConsumer<A1, ? super T> c1Accumulator =
Objects.requireNonNull(downstream1.accumulator(), "downstream1 accumulator");
BiConsumer<A2, ? super T> c2Accumulator =
Objects.requireNonNull(downstream2.accumulator(), "downstream2 accumulator");
BinaryOperator<A1> c1Combiner = Objects.requireNonNull(downstream1.combiner(), "downstream1 combiner");
BinaryOperator<A2> c2Combiner = Objects.requireNonNull(downstream2.combiner(), "downstream2 combiner");
Function<A1, R1> c1Finisher = Objects.requireNonNull(downstream1.finisher(), "downstream1 finisher");
Function<A2, R2> c2Finisher = Objects.requireNonNull(downstream2.finisher(), "downstream2 finisher");
Set<Collector.Characteristics> characteristics;
Set<Collector.Characteristics> c1Characteristics = downstream1.characteristics();
Set<Collector.Characteristics> c2Characteristics = downstream2.characteristics();
if (CH_ID.containsAll(c1Characteristics) || CH_ID.containsAll(c2Characteristics)) {
characteristics = CH_NOID;
} else {
EnumSet<Collector.Characteristics> c = EnumSet.noneOf(Collector.Characteristics.class);
c.addAll(c1Characteristics);
c.retainAll(c2Characteristics);
c.remove(Collector.Characteristics.IDENTITY_FINISH);
characteristics = Collections.unmodifiableSet(c);
}
class PairBox {
A1 left = c1Supplier.get();
A2 right = c2Supplier.get();
void add(T t) {
c1Accumulator.accept(left, t);
c2Accumulator.accept(right, t);
}
PairBox combine(PairBox other) {
left = c1Combiner.apply(left, other.left);
right = c2Combiner.apply(right, other.right);
return this;
}
R get() {
R1 r1 = c1Finisher.apply(left);
R2 r2 = c2Finisher.apply(right);
return merger.apply(r1, r2);
}
}
return new CollectorImpl<>(PairBox::new, PairBox::add, PairBox::combine, PairBox::get, characteristics);
}
/**
* Implementation class used by partitioningBy.
*/

67
test/jdk/java/util/stream/test/org/openjdk/tests/java/util/stream/CollectorsTest.java
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2012, 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -29,6 +29,7 @@ import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.IntSummaryStatistics;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
@ -39,6 +40,7 @@ import java.util.TreeMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentSkipListMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.BiFunction;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Predicate;
@ -96,7 +98,7 @@ public class CollectorsTest extends OpTestCase {
@Override
void assertValue(R value, Supplier<Stream<T>> source, boolean ordered) throws ReflectiveOperationException {
downstream.assertValue(value,
() -> source.get().map(mapper::apply),
() -> source.get().map(mapper),
ordered);
}
}
@ -114,7 +116,7 @@ public class CollectorsTest extends OpTestCase {
@Override
void assertValue(R value, Supplier<Stream<T>> source, boolean ordered) throws ReflectiveOperationException {
downstream.assertValue(value,
() -> source.get().flatMap(mapper::apply),
() -> source.get().flatMap(mapper),
ordered);
}
}
@ -287,6 +289,27 @@ public class CollectorsTest extends OpTestCase {
}
}
static class TeeingAssertion<T, R1, R2, RR> extends CollectorAssertion<T, RR> {
private final Collector<T, ?, R1> c1;
private final Collector<T, ?, R2> c2;
private final BiFunction<? super R1, ? super R2, ? extends RR> finisher;
TeeingAssertion(Collector<T, ?, R1> c1, Collector<T, ?, R2> c2,
BiFunction<? super R1, ? super R2, ? extends RR> finisher) {
this.c1 = c1;
this.c2 = c2;
this.finisher = finisher;
}
@Override
void assertValue(RR value, Supplier<Stream<T>> source, boolean ordered) {
R1 r1 = source.get().collect(c1);
R2 r2 = source.get().collect(c2);
RR expected = finisher.apply(r1, r2);
assertEquals(value, expected);
}
}
private <T> ResultAsserter<T> mapTabulationAsserter(boolean ordered) {
return (act, exp, ord, par) -> {
if (par && (!ordered || !ord)) {
@ -746,4 +769,42 @@ public class CollectorsTest extends OpTestCase {
catch (UnsupportedOperationException ignored) { }
}
@Test(dataProvider = "StreamTestData<Integer>", dataProviderClass = StreamTestDataProvider.class)
public void testTeeing(String name, TestData.OfRef<Integer> data) throws ReflectiveOperationException {
Collector<Integer, ?, Long> summing = Collectors.summingLong(Integer::valueOf);
Collector<Integer, ?, Long> counting = Collectors.counting();
Collector<Integer, ?, Integer> min = collectingAndThen(Collectors.<Integer>minBy(Comparator.naturalOrder()),
opt -> opt.orElse(Integer.MAX_VALUE));
Collector<Integer, ?, Integer> max = collectingAndThen(Collectors.<Integer>maxBy(Comparator.naturalOrder()),
opt -> opt.orElse(Integer.MIN_VALUE));
Collector<Integer, ?, String> joining = mapping(String::valueOf, Collectors.joining(", ", "[", "]"));
Collector<Integer, ?, Map.Entry<Long, Long>> sumAndCount = Collectors.teeing(summing, counting, Map::entry);
Collector<Integer, ?, Map.Entry<Integer, Integer>> minAndMax = Collectors.teeing(min, max, Map::entry);
Collector<Integer, ?, Double> averaging = Collectors.teeing(summing, counting,
(sum, count) -> ((double)sum) / count);
Collector<Integer, ?, String> summaryStatistics = Collectors.teeing(sumAndCount, minAndMax,
(sumCountEntry, minMaxEntry) -> new IntSummaryStatistics(
sumCountEntry.getValue(), minMaxEntry.getKey(),
minMaxEntry.getValue(), sumCountEntry.getKey()).toString());
Collector<Integer, ?, String> countAndContent = Collectors.teeing(counting, joining,
(count, content) -> count+": "+content);
assertCollect(data, sumAndCount, stream -> {
List<Integer> list = stream.collect(toList());
return Map.entry(list.stream().mapToLong(Integer::intValue).sum(), (long) list.size());
});
assertCollect(data, averaging, stream -> stream.mapToInt(Integer::intValue).average().orElse(Double.NaN));
assertCollect(data, summaryStatistics,
stream -> stream.mapToInt(Integer::intValue).summaryStatistics().toString());
assertCollect(data, countAndContent, stream -> {
List<Integer> list = stream.collect(toList());
return list.size()+": "+list;
});
Function<Integer, Integer> classifier = i -> i % 3;
exerciseMapCollection(data, groupingBy(classifier, sumAndCount),
new GroupingByAssertion<>(classifier, Map.class,
new TeeingAssertion<>(summing, counting, Map::entry)));
}
}