Add PageCollectors

src/main/java/org/springframework/data/util/PageCollectors.java

@@ -0,0 +1,278 @@
+package org.springframework.data.util;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+import java.util.function.BiConsumer;
+import java.util.function.BinaryOperator;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.function.Supplier;
+import java.util.stream.Collector;
+import java.util.stream.Collector.Characteristics;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.PageImpl;
+import org.springframework.data.domain.Pageable;
+
+public final class PageCollectors<T> {
+
+	private static final Set<Characteristics> characteristics = Collections.emptySet();
+
+	/**
+	 * Reduce the {@link Stream} as {@link Page} based on the {@link Pageable}
+	 * information.
+	 *
+	 * @param <T>
+	 * @param p
+	 * @return a {@link Page} containing a subset of the {@link Stream}
+	 */
+	public static <T> Collector<T, List<T>, Page<T>> toPage(final Pageable p) {
+		return new PageCollectorImpl<>(p);
+	}
+
+	private static class PageCollectorImpl<T> implements Collector<T, List<T>, Page<T>> {
+
+		Pageable p;
+
+		public PageCollectorImpl(final Pageable p) {
+			this.p = Objects.requireNonNull(p);
+		}
+
+		@Override
+		public Set<Characteristics> characteristics() {
+			return characteristics;
+		}
+
+		@Override
+		public Supplier<List<T>> supplier() {
+			return ArrayList::new;
+		}
+
+		@Override
+		public BiConsumer<List<T>, T> accumulator() {
+			return List::add;
+		}
+
+		@Override
+		public BinaryOperator<List<T>> combiner() {
+			return (left, right) -> {
+				left.addAll(right);
+				return left;
+			};
+		}
+
+		@Override
+		public Function<List<T>, Page<T>> finisher() {
+			return t -> {
+				final int pageNumber = p.getPageNumber();
+				final int pageSize = p.getPageSize();
+				final int fromIndex = Math.min(t.size(), pageNumber * pageSize);
+				final int toIndex = Math.min(t.size(), (pageNumber + 1) * pageSize);
+
+				return new PageImpl<>(t.subList(fromIndex, toIndex), p, t.size());
+			};
+		}
+
+	}
+
+	/**
+	 * Reduce the {@link Stream} as {@link Page} based on the {@link Pageable}
+	 * information.
+	 *
+	 * @param <T>
+	 * @param p
+	 * @return a {@link Page} containing a subset of the {@link Stream} sort
+	 *         following the {@link Comparator}
+	 */
+	public static <T> Collector<T, List<T>, Page<T>> toSortedPage(final Pageable p, final Comparator<T> c) {
+		return new SortedPageCollectorImpl<>(p, c);
+	}
+
+	private static class SortedPageCollectorImpl<T> implements Collector<T, List<T>, Page<T>> {
+
+		Pageable p;
+		Comparator<T> c;
+
+		public SortedPageCollectorImpl(final Pageable p, final Comparator<T> c) {
+			this.p = Objects.requireNonNull(p);
+			this.c = Objects.requireNonNull(c);
+		}
+
+		@Override
+		public Set<Characteristics> characteristics() {
+			return characteristics;
+		}
+
+		@Override
+		public Supplier<List<T>> supplier() {
+			return ArrayList::new;
+		}
+
+		@Override
+		public BiConsumer<List<T>, T> accumulator() {
+			return List::add;
+		}
+
+		@Override
+		public BinaryOperator<List<T>> combiner() {
+			return (left, right) -> {
+				left.addAll(right);
+				return left;
+			};
+		}
+
+		@Override
+		public Function<List<T>, Page<T>> finisher() {
+			return t -> {
+				final int pageNumber = p.getPageNumber();
+				final int pageSize = p.getPageSize();
+				final int fromIndex = Math.min(t.size(), pageNumber * pageSize);
+				final int toIndex = Math.min(t.size(), (pageNumber + 1) * pageSize);
+
+				final List<T> data = t.subList(fromIndex, toIndex);
+				data.sort(c);
+
+				return new PageImpl<>(data, p, t.size());
+			};
+		}
+
+	}
+
+	/**
+	 * Reduce the {@link Stream} as {@link Page} based on the {@link Pageable}
+	 * information. <br>
+	 *
+	 * <strong>The {@link Stream} is filtered before subset of data
+	 * isolated</strong>
+	 *
+	 * @param <T>
+	 * @param p
+	 * @return a {@link Page} containing a subset of the {@link Stream}
+	 */
+	public static <T> Collector<T, List<T>, Page<T>> toFilteredPage(final Pageable p, final Predicate<T> f) {
+		return new FilteredPageCollectorImpl<>(p, f);
+	}
+
+	private static class FilteredPageCollectorImpl<T> implements Collector<T, List<T>, Page<T>> {
+
+		Pageable p;
+		Predicate<T> f;
+
+		public FilteredPageCollectorImpl(final Pageable p, final Predicate<T> f) {
+			this.p = Objects.requireNonNull(p);
+			this.f = Objects.requireNonNull(f);
+		}
+
+		@Override
+		public Set<Characteristics> characteristics() {
+			return characteristics;
+		}
+
+		@Override
+		public Supplier<List<T>> supplier() {
+			return ArrayList::new;
+		}
+
+		@Override
+		public BiConsumer<List<T>, T> accumulator() {
+			return List::add;
+		}
+
+		@Override
+		public BinaryOperator<List<T>> combiner() {
+			return (left, right) -> {
+				left.addAll(right);
+				return left;
+			};
+		}
+
+		@Override
+		public Function<List<T>, Page<T>> finisher() {
+			return t -> {
+				final List<T> data = t.stream().filter(f).collect(Collectors.toList());
+
+				final int pageNumber = p.getPageNumber();
+				final int pageSize = p.getPageSize();
+				final int fromIndex = Math.min(data.size(), pageNumber * pageSize);
+				final int toIndex = Math.min(data.size(), (pageNumber + 1) * pageSize);
+
+				return new PageImpl<>(data.subList(fromIndex, toIndex), p, t.size());
+			};
+		}
+
+	}
+
+	/**
+	 * Reduce the {@link Stream} as {@link Page} based on the {@link Pageable}
+	 * information. <br>
+	 *
+	 * <strong>The {@link Stream} is filtered then sorted then the subset of data
+	 * isolated</strong>
+	 *
+	 * @param <T>
+	 * @param p
+	 * @return a {@link Page} containing a subset of the {@link Stream}
+	 */
+	public static <T> Collector<T, List<T>, Page<T>> toFilteredSortedPage(final Pageable p, final Predicate<T> f,
+			final Comparator<T> c) {
+		return new FilteredSortedPageCollectorImpl<>(p, f, c);
+	}
+
+	private static class FilteredSortedPageCollectorImpl<T> implements Collector<T, List<T>, Page<T>> {
+
+		Pageable p;
+		Predicate<T> f;
+		Comparator<T> c;
+
+		public FilteredSortedPageCollectorImpl(final Pageable p, final Predicate<T> f, final Comparator<T> c) {
+			this.p = Objects.requireNonNull(p);
+			this.f = Objects.requireNonNull(f);
+			this.c = Objects.requireNonNull(c);
+		}
+
+		@Override
+		public Set<Characteristics> characteristics() {
+			return characteristics;
+		}
+
+		@Override
+		public Supplier<List<T>> supplier() {
+			return ArrayList::new;
+		}
+
+		@Override
+		public BiConsumer<List<T>, T> accumulator() {
+			return List::add;
+		}
+
+		@Override
+		public BinaryOperator<List<T>> combiner() {
+			return (left, right) -> {
+				left.addAll(right);
+				return left;
+			};
+		}
+
+		@Override
+		public Function<List<T>, Page<T>> finisher() {
+			return t -> {
+				final List<T> data = t.stream().filter(f).sorted(c).collect(Collectors.toList());
+
+				final int pageNumber = p.getPageNumber();
+				final int pageSize = p.getPageSize();
+				final int fromIndex = Math.min(data.size(), pageNumber * pageSize);
+				final int toIndex = Math.min(data.size(), (pageNumber + 1) * pageSize);
+
+				return new PageImpl<>(data.subList(fromIndex, toIndex), p, t.size());
+			};
+		}
+
+	}
+
+}

src/test/java/org/springframework/data/util/PageCollectorsToFilteredPageTest.java

@@ -0,0 +1,84 @@
+package org.springframework.data.util;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertIterableEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Random;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.Pageable;
+
+public class PageCollectorsToFilteredPageTest {
+
+	private List<Integer> ints;
+	private int size;
+
+	@BeforeEach
+	void init() {
+		final Random rand = new Random();
+		size = rand.nextInt(10000);
+		ints = IntStream.range(0, size).mapToObj(i -> rand.nextInt()).collect(Collectors.toList());
+	}
+
+	@Test
+	void fullPage() {
+		final Pageable pageable = Pageable.ofSize(size);
+		final Page<Integer> page = ints.stream().collect(PageCollectors.toFilteredPage(pageable, i -> i > 0));
+
+		assertEquals(size, page.getSize());
+		assertTrue(page.getContent().size() <= size);
+		for (final Integer element : page.getContent()) {
+			assertTrue(element > 0);
+		}
+	}
+
+	@Test
+	void emptyPage() {
+		final Pageable pageable = Pageable.ofSize(size);
+		final Page<Integer> page = Collections.<Integer>emptyList().stream()
+				.collect(PageCollectors.toFilteredPage(pageable, i -> i > 0));
+
+		assertEquals(size, page.getSize());
+		assertTrue(page.getContent().isEmpty());
+	}
+
+	@Test
+	void secondPage() {
+		final Pageable pageable = Pageable.ofSize(size / 4).withPage(2);
+		final Page<Integer> page = ints.stream().collect(PageCollectors.toFilteredPage(pageable, i -> i < 0));
+
+		assertEquals(size / 4, page.getSize());
+		assertTrue(page.getContent().size() <= size);
+		for (final Integer element : page.getContent()) {
+			assertTrue(element < 0);
+		}
+	}
+
+	@Test
+	void checkData() {
+		final List<String> datas = Arrays.asList("un", "deux", "trois", "quatre", "cinq", "six", "sept", "huit", "neuf",
+				"dix");
+
+		final int size = datas.size();
+		final Pageable pageable = Pageable.ofSize(size / 2).withPage(0);
+		final Page<String> page = datas.stream().collect(PageCollectors.toFilteredPage(pageable, t -> t.contains("i")));
+
+		assertEquals(size / 2, page.getSize());
+		assertEquals(size / 2, page.getContent().size());
+		for (final String string : page.getContent()) {
+			assertTrue(string.contains("i"));
+			assertFalse(!string.contains("i"));
+		}
+		assertIterableEquals(page.getContent(), Arrays.asList("trois", "cinq", "six", "huit", "dix"));
+	}
+
+}