Introduce Scroll API.

See: #2151
Original Pull Request: #2787

src/main/java/org/springframework/data/domain/KeysetScrollPosition.java

@@ -0,0 +1,144 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.domain;
+
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
+
+/**
+ * A {@link ScrollPosition} based on the last seen keyset. Keyset scrolling must be associated with a {@link Sort
+ * well-defined sort} to be able to extract the keyset when resuming scrolling within the sorted result set.
+ *
+ * @author Mark Paluch
+ * @since 3.1
+ */
+public final class KeysetScrollPosition implements ScrollPosition {
+
+	private static final KeysetScrollPosition initial = new KeysetScrollPosition(Collections.emptyMap(),
+			Direction.Forward);
+
+	private final Map<String, Object> keys;
+
+	private final Direction direction;
+
+	private KeysetScrollPosition(Map<String, Object> keys, Direction direction) {
+		this.keys = keys;
+		this.direction = direction;
+	}
+
+	/**
+	 * Creates a new initial {@link KeysetScrollPosition} to start scrolling using keyset-queries.
+	 *
+	 * @return a new initial {@link KeysetScrollPosition} to start scrolling using keyset-queries.
+	 */
+	public static KeysetScrollPosition initial() {
+		return initial;
+	}
+
+	/**
+	 * Creates a new {@link KeysetScrollPosition} from a keyset.
+	 *
+	 * @param keys must not be {@literal null}.
+	 * @return a new {@link KeysetScrollPosition} for the given keyset.
+	 */
+	public static KeysetScrollPosition of(Map<String, ?> keys) {
+		return of(keys, Direction.Forward);
+	}
+
+	/**
+	 * Creates a new {@link KeysetScrollPosition} from a keyset and {@link Direction}.
+	 *
+	 * @param keys must not be {@literal null}.
+	 * @param direction must not be {@literal null}.
+	 * @return a new {@link KeysetScrollPosition} for the given keyset and {@link Direction}.
+	 */
+	public static KeysetScrollPosition of(Map<String, ?> keys, Direction direction) {
+
+		Assert.notNull(keys, "Keys must not be null");
+		Assert.notNull(direction, "Direction must not be null");
+
+		if (keys.isEmpty()) {
+			return initial();
+		}
+
+		return new KeysetScrollPosition(Collections.unmodifiableMap(new LinkedHashMap<>(keys)), direction);
+	}
+
+	@Override
+	public boolean isInitial() {
+		return keys.isEmpty();
+	}
+
+	/**
+	 * @return the keyset.
+	 */
+	public Map<String, Object> getKeys() {
+		return keys;
+	}
+
+	/**
+	 * @return the scroll direction.
+	 */
+	public Direction getDirection() {
+		return direction;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o)
+			return true;
+		if (o == null || getClass() != o.getClass())
+			return false;
+		KeysetScrollPosition that = (KeysetScrollPosition) o;
+		return ObjectUtils.nullSafeEquals(keys, that.keys) && direction == that.direction;
+	}
+
+	@Override
+	public int hashCode() {
+
+		int result = 17;
+
+		result += 31 * ObjectUtils.nullSafeHashCode(keys);
+		result += 31 * ObjectUtils.nullSafeHashCode(direction);
+
+		return result;
+	}
+
+	@Override
+	public String toString() {
+		return String.format("KeysetScrollPosition [%s, %s]", direction, keys);
+	}
+
+	/**
+	 * Keyset scrolling direction.
+	 */
+	enum Direction {
+
+		/**
+		 * Forward (default) direction to scroll from the beginning of the results to their end.
+		 */
+		Forward,
+
+		/**
+		 * Backward direction to scroll from the end of the results to their beginning.
+		 */
+		Backward;
+	}
+}

src/main/java/org/springframework/data/domain/OffsetScrollPosition.java

@@ -0,0 +1,127 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.domain;
+
+import java.util.function.IntFunction;
+
+import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
+
+/**
+ * A {@link ScrollPosition} based on the offsets within query results.
+ *
+ * @author Mark Paluch
+ * @since 3.1
+ */
+public final class OffsetScrollPosition implements ScrollPosition {
+
+	private static final OffsetScrollPosition initial = new OffsetScrollPosition(0);
+
+	private final long offset;
+
+	private OffsetScrollPosition(long offset) {
+		this.offset = offset;
+	}
+
+	/**
+	 * Creates a new initial {@link OffsetScrollPosition} to start scrolling using offset/limit.
+	 *
+	 * @return a new initial {@link OffsetScrollPosition} to start scrolling using offset/limit.
+	 */
+	public static OffsetScrollPosition initial() {
+		return initial;
+	}
+
+	/**
+	 * Creates a new {@link OffsetScrollPosition} from an {@code offset}.
+	 *
+	 * @param offset
+	 * @return a new {@link OffsetScrollPosition} with the given {@code offset}.
+	 */
+	public static OffsetScrollPosition of(long offset) {
+
+		if (offset == 0) {
+			return initial();
+		}
+
+		return new OffsetScrollPosition(offset);
+	}
+
+	/**
+	 * Returns the {@link IntFunction position function} to calculate.
+	 *
+	 * @param startOffset the start offset to be used. Must not be negative.
+	 * @return the offset-based position function.
+	 */
+	public static IntFunction<OffsetScrollPosition> positionFunction(long startOffset) {
+
+		Assert.isTrue(startOffset >= 0, "Start offset must not be negative");
+
+		return startOffset == 0 ? OffsetPositionFunction.ZERO : new OffsetPositionFunction(startOffset);
+	}
+
+	@Override
+	public boolean isInitial() {
+		return offset == 0;
+	}
+
+	/**
+	 * @return the offset.
+	 */
+	public long getOffset() {
+		return offset;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o)
+			return true;
+		if (o == null || getClass() != o.getClass())
+			return false;
+		OffsetScrollPosition that = (OffsetScrollPosition) o;
+		return offset == that.offset;
+	}
+
+	@Override
+	public int hashCode() {
+
+		int result = 17;
+
+		result += 31 * ObjectUtils.nullSafeHashCode(offset);
+
+		return result;
+	}
+
+	@Override
+	public String toString() {
+		return String.format("OffsetScrollPosition [%s]", offset);
+	}
+
+	private record OffsetPositionFunction(long startOffset) implements IntFunction<OffsetScrollPosition> {
+
+		static final OffsetPositionFunction ZERO = new OffsetPositionFunction(0);
+
+		@Override
+		public OffsetScrollPosition apply(int offset) {
+
+			if (offset < 0) {
+				throw new IndexOutOfBoundsException(offset);
+			}
+
+			return of(startOffset + offset + 1);
+		}
+	}
+}

src/main/java/org/springframework/data/domain/Pageable.java

@@ -161,4 +161,20 @@ public interface Pageable {
 		return isUnpaged() ? Optional.empty() : Optional.of(this);
 	}
 
+	/**
+	 * Returns an {@link OffsetScrollPosition} from this pageable if the page request {@link #isPaged() is paged}.
+	 *
+	 * @return
+	 * @throws IllegalStateException if the request is {@link #isUnpaged()}
+	 * @since 3.1
+	 */
+	default OffsetScrollPosition toScrollPosition() {
+
+		if (isUnpaged()) {
+			throw new IllegalStateException("Cannot create OffsetScrollPosition from an unpaged instance");
+		}
+
+		return OffsetScrollPosition.of(getOffset());
+	}
+
 }

src/main/java/org/springframework/data/domain/Scroll.java

@@ -0,0 +1,167 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.domain;
+
+import java.util.List;
+import java.util.NoSuchElementException;
+import java.util.function.Function;
+import java.util.function.IntFunction;
+
+import org.springframework.data.util.Streamable;
+
+/**
+ * A scroll of data consumed from an underlying query result. A scroll is similar to {@link Slice} in the sense that it
+ * contains a subset of the actual query results for easier consumption of large result sets. The scroll is less
+ * opinionated about the actual data retrieval, whether the query has used index/offset, keyset-based pagination or
+ * cursor resume tokens.
+ *
+ * @author Mark Paluch
+ * @since 3.1
+ * @see ScrollPosition
+ */
+public interface Scroll<T> extends Streamable<T> {
+
+	/**
+	 * Construct a {@link Scroll}.
+	 *
+	 * @param items the list of data.
+	 * @param positionFunction the list of data.
+	 * @return the {@link Scroll}.
+	 * @param <T>
+	 */
+	static <T> Scroll<T> from(List<T> items, IntFunction<? extends ScrollPosition> positionFunction) {
+		return new ScrollImpl<>(items, positionFunction, false);
+	}
+
+	/**
+	 * Construct a {@link Scroll}.
+	 *
+	 * @param items the list of data.
+	 * @param positionFunction the list of data.
+	 * @param hasNext
+	 * @return the {@link Scroll}.
+	 * @param <T>
+	 */
+	static <T> Scroll<T> from(List<T> items, IntFunction<? extends ScrollPosition> positionFunction, boolean hasNext) {
+		return new ScrollImpl<>(items, positionFunction, hasNext);
+	}
+
+	/**
+	 * Returns the number of elements in this scroll.
+	 *
+	 * @return the number of elements in this scroll.
+	 */
+	int size();
+
+	/**
+	 * Returns {@code true} if this scroll contains no elements.
+	 *
+	 * @return {@code true} if this scroll contains no elements
+	 */
+	boolean isEmpty();
+
+	/**
+	 * Returns the scroll content as {@link List}.
+	 *
+	 * @return
+	 */
+	List<T> getContent();
+
+	/**
+	 * Returns whether the current scroll is the last one.
+	 *
+	 * @return
+	 */
+	default boolean isLast() {
+		return !hasNext();
+	}
+
+	/**
+	 * Returns if there is a next scroll.
+	 *
+	 * @return if there is a next scroll window.
+	 */
+	boolean hasNext();
+
+	/**
+	 * Returns the {@link ScrollPosition} at {@code index}.
+	 *
+	 * @param index
+	 * @return
+	 * @throws IndexOutOfBoundsException if the index is out of range ({@code index < 0 || index >= size()}).
+	 */
+	ScrollPosition positionAt(int index);
+
+	/**
+	 * Returns the {@link ScrollPosition} for {@code object}.
+	 *
+	 * @param object
+	 * @return
+	 * @throws NoSuchElementException if the object is not part of the result.
+	 */
+	default ScrollPosition positionAt(T object) {
+
+		int index = getContent().indexOf(object);
+
+		if (index == -1) {
+			throw new NoSuchElementException();
+		}
+
+		return positionAt(index);
+	}
+
+	// TODO: First and last seem to conflict with first/last scroll or first/last position of elements.
+	// these methods should rather express the position of the first element within this scroll and the scroll position
+	// to be used to get the next Scroll.
+	/**
+	 * Returns the first {@link ScrollPosition} or throw {@link NoSuchElementException} if the list is empty.
+	 *
+	 * @return the first {@link ScrollPosition}.
+	 * @throws NoSuchElementException if this result is empty.
+	 */
+	default ScrollPosition firstPosition() {
+
+		if (size() == 0) {
+			throw new NoSuchElementException();
+		}
+
+		return positionAt(0);
+	}
+
+	/**
+	 * Returns the last {@link ScrollPosition} or throw {@link NoSuchElementException} if the list is empty.
+	 *
+	 * @return the last {@link ScrollPosition}.
+	 * @throws NoSuchElementException if this result is empty.
+	 */
+	default ScrollPosition lastPosition() {
+
+		if (size() == 0) {
+			throw new NoSuchElementException();
+		}
+
+		return positionAt(size() - 1);
+	}
+
+	/**
+	 * Returns a new {@link Scroll} with the content of the current one mapped by the given {@code converter}.
+	 *
+	 * @param converter must not be {@literal null}.
+	 * @return a new {@link Scroll} with the content of the current one mapped by the given {@code converter}.
+	 */
+	<U> Scroll<U> map(Function<? super T, ? extends U> converter);
+
+}

src/main/java/org/springframework/data/domain/ScrollImpl.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.domain;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Function;
+import java.util.function.IntFunction;
+import java.util.stream.Collectors;
+
+import org.jetbrains.annotations.NotNull;
+import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
+
+/**
+ * Default {@link Scroll} implementation.
+ *
+ * @author Mark Paluch
+ * @since 3.1
+ */
+class ScrollImpl<T> implements Scroll<T> {
+
+	private final List<T> items;
+	private final IntFunction<? extends ScrollPosition> positionFunction;
+
+	private final boolean hasNext;
+
+	ScrollImpl(List<T> items, IntFunction<? extends ScrollPosition> positionFunction, boolean hasNext) {
+
+		Assert.notNull(items, "List of items must not be null");
+		Assert.notNull(positionFunction, "Position function must not be null");
+
+		this.items = items;
+		this.positionFunction = positionFunction;
+		this.hasNext = hasNext;
+	}
+
+	@Override
+	public int size() {
+		return items.size();
+	}
+
+	@Override
+	public boolean isEmpty() {
+		return items.isEmpty();
+	}
+
+	@Override
+	public List<T> getContent() {
+		return items;
+	}
+
+	@Override
+	public boolean hasNext() {
+		return hasNext;
+	}
+
+	@Override
+	public ScrollPosition positionAt(int index) {
+
+		if (index < 0 || index >= size()) {
+			throw new IndexOutOfBoundsException(index);
+		}
+
+		return positionFunction.apply(index);
+	}
+
+	@Override
+	public <U> Scroll<U> map(Function<? super T, ? extends U> converter) {
+
+		Assert.notNull(converter, "Function must not be null");
+
+		return new ScrollImpl<>(stream().map(converter).collect(Collectors.toList()), positionFunction, hasNext);
+	}
+
+	@NotNull
+	@Override
+	public Iterator<T> iterator() {
+		return items.iterator();
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o)
+			return true;
+		if (o == null || getClass() != o.getClass())
+			return false;
+		ScrollImpl<?> that = (ScrollImpl<?>) o;
+		return ObjectUtils.nullSafeEquals(items, that.items)
+				&& ObjectUtils.nullSafeEquals(positionFunction, that.positionFunction)
+				&& ObjectUtils.nullSafeEquals(hasNext, that.hasNext);
+	}
+
+	@Override
+	public int hashCode() {
+		int result = ObjectUtils.nullSafeHashCode(items);
+		result = 31 * result + ObjectUtils.nullSafeHashCode(positionFunction);
+		result = 31 * result + ObjectUtils.nullSafeHashCode(hasNext);
+		return result;
+	}
+
+	@Override
+	public String toString() {
+		return "Scroll " + items;
+	}
+}

src/main/java/org/springframework/data/domain/ScrollPosition.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.domain;
+
+/**
+ * Interface to specify a position within a total query result. Scroll positions are used to start scrolling from the
+ * beginning of a query result or to resume scrolling from a given position within the query result.
+ *
+ * @author Mark Paluch
+ * @since 3.1
+ */
+public interface ScrollPosition {
+
+	/**
+	 * Returns whether the current scroll position is the initial one.
+	 *
+	 * @return
+	 */
+	boolean isInitial();
+}