java.util.stream.Collector Java Examples

public void collector02Example(SqlClient client) {

    // Create a collector projecting a row set to a (last_name_1,last_name_2,...)
    Collector<Row, ?, String> collector = Collectors.mapping(
      row -> row.getString("last_name"),
      Collectors.joining(",", "(", ")")
    );

    // Run the query with the collector
    client.query("SELECT * FROM users").collecting(collector).execute(ar -> {
        if (ar.succeeded()) {
          SqlResult<String> result = ar.result();

          // Get the string created by the collector
          String list = result.value();
          System.out.println("Got " + list);
        } else {
          System.out.println("Failure: " + ar.cause().getMessage());
        }
      });
  }
 

@Test
public void testGetNameThatIsntUsed() throws InterruptedException, TimeoutException {
  try (Session session = ds.getSession()) {
    CompletionStage<Integer> idF = session.<Integer>rowOperation("select 100 as t")
        .collect(Collector.of(
            () -> new int[1],
            (a, r) -> a[0] = r.at("notused").get(Integer.class),
            (l, r) -> null,
            a -> a[0])
        )
        .submit()
        .getCompletionStage();

    get10(idF);
    fail("the column 'notused' doesn't exist in the result.row and should result in an IllegalArgumentException");
  } catch (ExecutionException e) {
    IllegalArgumentException ex = (IllegalArgumentException)e.getCause();

    assertEquals("no column with id notused", ex.getMessage());
  }
}
 

private<T, M extends Map>
void exerciseMapTabulation(TestData<T, Stream<T>> data,
                           Collector<T, ?, ? extends M> collector,
                           TabulationAssertion<T, M> assertion)
        throws ReflectiveOperationException {
    boolean ordered = !collector.characteristics().contains(Collector.Characteristics.UNORDERED);

    M m = withData(data)
            .terminal(s -> s.collect(collector))
            .resultAsserter(mapTabulationAsserter(ordered))
            .exercise();
    assertion.assertValue(m, () -> data.stream(), ordered);

    m = withData(data)
            .terminal(s -> s.unordered().collect(collector))
            .resultAsserter(mapTabulationAsserter(ordered))
            .exercise();
    assertion.assertValue(m, () -> data.stream(), false);
}
 

private<T, M extends Map>
void exerciseMapTabulation(TestData<T, Stream<T>> data,
                           Collector<T, ?, ? extends M> collector,
                           TabulationAssertion<T, M> assertion)
        throws ReflectiveOperationException {
    boolean ordered = !collector.characteristics().contains(Collector.Characteristics.UNORDERED);

    M m = withData(data)
            .terminal(s -> s.collect(collector))
            .resultAsserter(mapTabulationAsserter(ordered))
            .exercise();
    assertion.assertValue(m, () -> data.stream(), ordered);

    m = withData(data)
            .terminal(s -> s.unordered().collect(collector))
            .resultAsserter(mapTabulationAsserter(ordered))
            .exercise();
    assertion.assertValue(m, () -> data.stream(), false);
}
 

public void collector02Example(SqlClient client) {

    // Create a collector projecting a row set to a (last_name_1,last_name_2,...)
    Collector<Row, ?, String> collector = Collectors.mapping(
      row -> row.getString("last_name"),
      Collectors.joining(",", "(", ")")
    );

    // Run the query with the collector
    client.query("SELECT * FROM users")
      .collecting(collector)
      .execute(ar -> {
        if (ar.succeeded()) {
          SqlResult<String> result = ar.result();

          // Get the string created by the collector
          String list = result.value();
          System.out.println("Got " + list);
        } else {
          System.out.println("Failure: " + ar.cause().getMessage());
        }
      });
  }
 

@Test(dataProvider = "StreamTestData<Integer>", dataProviderClass = StreamTestDataProvider.class)
public void testOps(String name, TestData.OfRef<Integer> data) {
    // @@@ More things to test here:
    //     - Every value in data is present in right bucket
    //     - Total number of values equals size of data

    for (MapperData<Integer, ?> md : getMapperData(data)) {
        Collector<Integer, ?, Map<Object, List<Integer>>> tab = Collectors.groupingBy(md.m);
        Map<Object, List<Integer>> result =
                withData(data)
                .terminal(s -> s, s -> s.collect(tab))
                .resultAsserter((act, exp, ord, par) -> {
                    if (par & !ord) {
                        GroupByOpTest.assertMultiMapEquals(act, exp);
                    }
                    else {
                        GroupByOpTest.assertObjectEquals(act, exp);
                    }
                })
                .exercise();
        assertEquals(result.keySet().size(), md.expectedSize);
    }
}
 

@Test(dataProvider = "StreamTestData<Integer>", dataProviderClass = StreamTestDataProvider.class)
public void testOps(String name, TestData.OfRef<Integer> data) {
    // @@@ More things to test here:
    //     - Every value in data is present in right bucket
    //     - Total number of values equals size of data

    for (MapperData<Integer, ?> md : getMapperData(data)) {
        Collector<Integer, ?, Map<Object, List<Integer>>> tab = Collectors.groupingBy(md.m);
        Map<Object, List<Integer>> result =
                withData(data)
                .terminal(s -> s, s -> s.collect(tab))
                .resultAsserter((act, exp, ord, par) -> {
                    if (par & !ord) {
                        GroupByOpTest.assertMultiMapEquals(act, exp);
                    }
                    else {
                        GroupByOpTest.assertObjectEquals(act, exp);
                    }
                })
                .exercise();
        assertEquals(result.keySet().size(), md.expectedSize);
    }
}
 

public static <T, K, V> Collector<T, ImmutableMap.Builder<K, V>, ImmutableMap<K, V>> toImmutableMap(
    Function<? super T, ? extends K> keyMapper,
    Function<? super T, ? extends V> valueMapper
) {
    return Collector.of(
        ImmutableMap.Builder<K, V>::new,
        (r, t) -> r.put(keyMapper.apply(t), valueMapper.apply(t)),
        (l, r) -> l.putAll(r.build()),
        ImmutableMap.Builder::build,
        Collector.Characteristics.UNORDERED
    );
}
 

@Test
public void testCollector(){
    Collector<Integer, ?, List<Integer>> list = Collectors.toList();
    List<Integer> res= null;
    res =Stream.of(1,2,3)
                .map(i->i+2)
                .collect(list);
    System.out.println("res " + res);
 //   Stream.of(1,2,3).collect((Supplier)list.supplier(),list.accumulator(),list.combiner());
}
 

default <R1, R2, A1, A2> Tuple2<R1, R2> collect(Collector<? super T, A1, R1> c1, Collector<? super T, A2, R2> c2) {
    return stream().collect(Collector.of(() -> Tuple.tuple(c1.supplier().get(),c2.supplier().get()),
            (t2, next) -> {
                c1.accumulator().accept(t2._1(), next);
                c2.accumulator().accept(t2._2(), next);
            },(t2, t2b) -> Tuple.tuple(c1.combiner().apply(t2._1(), t2b._1()),c2.combiner().apply(t2._2(), t2b._2())),
            t2 -> Tuple.tuple(c1.finisher().apply(t2._1()),c2.finisher().apply(t2._2()))));
}
 

@Test
public void testMapping() {
    assertThrows(NullPointerException.class, () -> MoreCollectors.mapping(null, Collectors.toList()));
    assertThrows(NullPointerException.class, () -> MoreCollectors.mapping(Function.identity(), null));
    List<String> input = asList("Capital", "lower", "Foo", "bar");
    Collector<String, ?, Map<Boolean, Optional<Integer>>> collector = MoreCollectors
            .partitioningBy(str -> Character.isUpperCase(str.charAt(0)), MoreCollectors.mapping(String::length,
                MoreCollectors.first()));
    checkShortCircuitCollector("mapping", new BooleanMap<>(Optional.of(7), Optional.of(5)), 2, input::stream,
        collector);
    Collector<String, ?, Map<Boolean, Optional<Integer>>> collectorLast = MoreCollectors.partitioningBy(
        str -> Character.isUpperCase(str.charAt(0)), MoreCollectors.mapping(String::length, MoreCollectors.last()));
    checkCollector("last", new BooleanMap<>(Optional.of(3), Optional.of(3)), input::stream, collectorLast);

    input = asList("Abc", "Bac", "Aac", "Abv", "Bbc", "Bgd", "Atc", "Bpv");
    Map<Character, List<String>> expected = EntryStream.of('A', asList("Abc", "Aac"), 'B', asList("Bac", "Bbc"))
            .toMap();
    AtomicInteger cnt = new AtomicInteger();
    Collector<String, ?, Map<Character, List<String>>> groupMap = Collectors.groupingBy(s -> s.charAt(0),
        MoreCollectors.mapping(x -> {
            cnt.incrementAndGet();
            return x;
        }, MoreCollectors.head(2)));
    checkCollector("groupMap", expected, input::stream, groupMap);
    cnt.set(0);
    assertEquals(expected, input.stream().collect(groupMap));
    assertEquals(4, cnt.get());

    checkCollector("mapping-toList", asList("a", "b", "c"), asList("a1", "b2", "c3")::stream, MoreCollectors
            .mapping(str -> str.substring(0, 1)));
}
 

public static final Collector<WebuiRelatedProcessDescriptor, ?, JSONDocumentActionsList> collect(final JSONOptions jsonOpts)
{
	final Supplier<List<WebuiRelatedProcessDescriptor>> supplier = ArrayList::new;
	final BiConsumer<List<WebuiRelatedProcessDescriptor>, WebuiRelatedProcessDescriptor> accumulator = List::add;
	final BinaryOperator<List<WebuiRelatedProcessDescriptor>> combiner = (l, r) -> {
		l.addAll(r);
		return l;
	};
	final Function<List<WebuiRelatedProcessDescriptor>, JSONDocumentActionsList> finisher = processDescriptors -> new JSONDocumentActionsList(processDescriptors, jsonOpts);
	return Collector.of(supplier, accumulator, combiner, finisher);
}
 

public MapCoercer(
    Class<T> stereotype,
    JsonTypeCoercer coercer,
    Collector<Map.Entry<?, ?>, ?, ? extends T> collector) {
  this.stereotype = stereotype;
  this.coercer = coercer;
  this.collector = collector;
}
 

@Test(dataProvider = "maps")
public void testPutThenTraverse(String d, Map<HashCodeInteger, Integer> m) {
    Collector<Integer, ?, ? extends Collection<Integer>> c = getCollector(m);

    put(SIZE, m, (i, s) -> {
        // Note that it is OK to collect to a Set (HashSet) as long as
        // integer values are used since these tests only check for
        // collisions and other tests will verify more general functionality
        Collection<Integer> actual = m.keySet().stream().map(e -> e.value).collect(c);
        Collection<Integer> expected = IntStream.range(0, s).boxed().collect(c);
        assertEquals(actual, expected, "Map.keySet()");
    });
}
 

public static <T, A, R> Collector<CompletableFuture<T>, ?, CompletableFuture<R>> toFuture(
        Supplier<A> identitySupplier, BiFunction<T, A, A> reducer, BinaryOperator<A> combiner, Function<? super A, ? extends R> completer) {
    return Collector.of(
                () -> FutureReducer.of(identitySupplier.get(), reducer, combiner),
                FutureReducer::addFuture,
                FutureReducer::combine,
                fr -> fr.complete().thenApply(completer));
}
 

private CollectorCtType newCollectorCtType(TypeMirror type) {
  DeclaredType declaredType = getSuperDeclaredType(type, Collector.class);
  if (declaredType == null) {
    return null;
  }
  Iterator<? extends TypeMirror> typeArgs = declaredType.getTypeArguments().iterator();
  CtType targetCtType = typeArgs.hasNext() ? newCtType(typeArgs.next()) : newNoneCtType();
  @SuppressWarnings("unused")
  CtType secondCtType = typeArgs.hasNext() ? newCtType(typeArgs.next()) : newNoneCtType();
  CtType returnCtType = typeArgs.hasNext() ? newCtType(typeArgs.next()) : newNoneCtType();
  return new CollectorCtType(ctx, type, targetCtType, returnCtType);
}
 

/**
 * Return a collector which calculates the bounds of a given way-point
 * stream. The following example shows how to calculate the bounds of all
 * track-points of a given GPX object.
 *
 * <pre>{@code
 * final Bounds bounds = gpx.tracks()
 *     .flatMap(Track::segments)
 *     .flatMap(TrackSegment::points)
 *     .collect(Bounds.toBounds());
 * }</pre>
 *
 * If the collecting way-point stream is empty, the collected {@code Bounds}
 * object is {@code null}.
 *
 * @since 1.6
 *
 * @param <P> The actual point type
 * @return a new bounds collector
 */
public static <P extends Point> Collector<P, ?, Bounds> toBounds() {
	return Collector.of(
		() -> {
			final double[] a = new double[4];
			a[0] = Double.MAX_VALUE;
			a[1] = Double.MAX_VALUE;
			a[2] = -Double.MAX_VALUE;
			a[3] = -Double.MAX_VALUE;
			return a;
		},
		(a, b) -> {
			a[0] = min(b.getLatitude().doubleValue(), a[0]);
			a[1] = min(b.getLongitude().doubleValue(), a[1]);
			a[2] = max(b.getLatitude().doubleValue(), a[2]);
			a[3] = max(b.getLongitude().doubleValue(), a[3]);
		},
		(a, b) -> {
			a[0] = min(a[0], b[0]);
			a[1] = min(a[1], b[1]);
			a[2] = max(a[2], b[2]);
			a[3] = max(a[3], b[3]);
			return a;
		},
		a -> a[0] == Double.MAX_VALUE
			? null
			: Bounds.of(a[0], a[1], a[2], a[3])
	);
}
 

/**
 * Collect a single element.
 *
 * The Collector throws {@link IllegalArgumentException} if no or more than one element.
 *
 * @param <T> Element type
 * @return The single element collector
 */
public static <T>
Collector<T, ?, T> single()
    throws IllegalArgumentException
{
    Supplier<T> thrower = () ->
    {
        throw new IllegalArgumentException( "No or more than one element in stream" );
    };
    return java.util.stream.Collectors.collectingAndThen( java.util.stream.Collectors.reducing( ( a, b ) -> null ),
                                                          optional -> optional.orElseGet( thrower ) );
}
 

/**
 * Combines multiple {@code Optional-}returning collector cases, to collect to the first non-empty
 * result. For example:
 *
 * <pre>{@code
 * Name name = nameParts.stream()
 *     .collect(switching(
 *         when(QualifiedName::new),                // (namespace, name) ->
 *         when(keywords::contains, Keyword::new),  // (keyword) ->
 *         when(UnqualifiedName::)                  // (name) ->
 *         when(Anonymous::new)));                  // () ->
 * }</pre>
 */
@SafeVarargs
public static <T, R> Collector<T, ?, R> switching(
    Collector<? super T, ?, ? extends Optional<? extends R>>... cases) {
  List<Collector<? super T, ?, ? extends Optional<? extends R>>> caseList =
      Arrays.stream(cases).peek(Objects::requireNonNull).collect(toList());
  return collectingAndThen(
      toList(),
      input ->
          caseList.stream()
              .map(c -> input.stream().collect(c).orElse(null))
              .filter(v -> v != null)
              .findFirst()
              .orElseThrow(() -> unexpectedSize(input.size())));
}
 

public QueryExecutor(QueryTracer tracer,
                     ClientMetrics metrics,
                     Function<T, R> factory,
                     Collector<Row, ?, T> collector) {
  this.tracer = tracer;
  this.metrics = metrics;
  this.factory = factory;
  this.collector = collector;
}
 

@Test
public void testOnlyIncluding() {
    Collector<String, ?, List<String>> nullExcludingListCollector =
            MoreCollectors.including(s -> s != null && s.length() > 1, toList());
    List<String> pFruit = Stream.of(null, null, "Pineapple",
            "Papaya", null, "Peach", "Plum", null,
            "Pear")
            .collect(nullExcludingListCollector);
    assertEquals(
            "Pineapple, Papaya, Peach, Plum, Pear",
            pFruit.stream().collect(MoreCollectors.joining(", "))
    );
}
 

/**
 * A collector which will convert a stream of {@link Measurement} instances into a {@link Model}.
 *
 * @return a {@link Collector} instance
 */
public static Collector<Measurement, List<Measurement>, Model> toModel() {
  return Collector.of(
      ArrayList::new,
      List::add,
      (a, b) -> {
        a.addAll(b);
        return a;
      },
      Model::build);
}
 

@Test
public void testMinMax() {
    assertThrows(NullPointerException.class, () -> MoreCollectors.minMax(null, String::concat));
    assertThrows(NullPointerException.class, () -> MoreCollectors.minMax(Comparator.naturalOrder(), null));
    List<String> input = asList("abc", "a", "asdf", "gdasa", "gffsd", "sfgs", "b", "c", "dsgs");
    checkCollector("minMax", Optional.of("agdasa"), input::stream, MoreCollectors.minMax(Comparator
            .comparingInt(String::length), String::concat));
    Collector<String, ?, Optional<Object>> collector = MoreCollectors.minMax(Comparator.naturalOrder(),
        (min, max) -> {
            throw new IllegalStateException("Should not be called");
        });
    checkCollectorEmpty("minMax", Optional.empty(), collector);
}
 

@Override
public String toString() {
    final Collector<CharSequence, ?, String> joiner;
    if (fields.size() == 1)
        joiner = Collectors.joining(", ");
    else
        joiner = Collectors.joining(", ", "(", ")");

    return fields.stream()
            .map(ResolverTuple::fieldString)
            .collect(joiner);
}
 

@Override
public @Nullable Object parseParameter(Map<String, List<String>> parameters) throws MalformedValueException {
  List<String> values = parameters.remove(parameterName);
  if (values == null) return null;
  return IntStream
    .range(0, values.size())
    .mapToObj(i -> parseItem(i, values.get(i)))
    .flatMap(Function.identity())
    .collect(Collector.of(JsonArray::new, JsonArray::add, JsonArray::addAll));
}
 

/**
 * Returns a collector which forms a JsonArray using the value mapper
 *
 * @param valueMapper the function to map from T to {@link JsonElement}
 * @param <T> the type
 * @return a new collector
 */
public static <T> Collector<T, JsonArrayBuilder, JsonArray> collectToArray(Function<? super T, JsonElement> valueMapper) {
    return Collector.of(
            JsonBuilder::array,
            (r, t) -> r.add(valueMapper.apply(t)),
            (l, r) -> l.addAll(r.build()),
            JsonArrayBuilder::build
    );
}
 

@Override
public PluralFieldBuildProcessor<D, S, T, L> collect(Collector<T, ?, L> collector) {
    if (this.collector != null)
        throw new IllegalStateException("Can't call collector twice");
    this.collector = (Collector<T, L, L>) collector;
    return this;
}
 

@Test(dataProvider = "maps")
public void testPutThenTraverse(String d, Map<HashCodeInteger, Integer> m) {
    Collector<Integer, ?, ? extends Collection<Integer>> c = getCollector(m);

    put(SIZE, m, (i, s) -> {
        // Note that it is OK to collect to a Set (HashSet) as long as
        // integer values are used since these tests only check for
        // collisions and other tests will verify more general functionality
        Collection<Integer> actual = m.keySet().stream().map(e -> e.value).collect(c);
        Collection<Integer> expected = IntStream.range(0, s).boxed().collect(c);
        assertEquals(actual, expected, "Map.keySet()");
    });
}
 

@Override
public <T1> LazySortedSetX<T1> from(Iterable<T1> c) {
    if(c instanceof Set)
        return new LazySortedSetX<T1>((SortedSet)c,null,(Collector)this.getCollectorInternal(), evaluation());
    return fromStream(ReactiveSeq.fromIterable(c));
}
 

private<T, R> void assertCollect(TestData.OfRef<T> data,
                                 Collector<T, ?, R> collector,
                                 Function<Stream<T>, R> streamReduction) {
    R check = streamReduction.apply(data.stream());
    withData(data).terminal(s -> s.collect(collector)).expectedResult(check).exercise();
}