Polishing Window scrolling API.

Moved general-purpose factory methods to the common ScrollPosition interface. Introduced a couple of domain specific methods to conveniently work with both Keyset- (to e.g. change direction) and OffsetScrollPosition (to e.g. advance the offset). Consolidated unit tests accordingly.

Moved WindowIterator to ….data.support package. Fixed case of Direction enum values.

Fixes #2824.

Author: odrotbohm

src/main/asciidoc/repositories-paging-sorting.adoc

@@ -14,7 +14,7 @@ Page<User> findByLastname(String lastname, Pageable pageable);
 
 Slice<User> findByLastname(String lastname, Pageable pageable);
 
-Scroll<User> findTop10ByLastname(String lastname, ScrollPosition position, Sort sort);
+Window<User> findTop10ByLastname(String lastname, ScrollPosition position, Sort sort);
 
 List<User> findByLastname(String lastname, Sort sort);
 

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

@@ -18,72 +18,61 @@
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.Objects;
 
+import org.springframework.lang.Nullable;
 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.
+ * A {@link ScrollPosition} based on the last seen key set. Keyset scrolling must be associated with a {@link Sort
+ * well-defined sort} to be able to extract the key set when resuming scrolling within the sorted result set.
  *
  * @author Mark Paluch
+ * @author Oliver Drotbohm
  * @since 3.1
  */
 public final class KeysetScrollPosition implements ScrollPosition {
 
-	private static final KeysetScrollPosition initial = new KeysetScrollPosition(Collections.emptyMap(),
-			Direction.Forward);
+	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) {
+
+		Assert.notNull(keys, "Keys must not be null");
+		Assert.notNull(direction, "Direction must not be null");
+
 		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.
+	 * @return will never be {@literal null}.
 	 */
-	public static KeysetScrollPosition of(Map<String, ?> keys) {
-		return of(keys, Direction.Forward);
+	static KeysetScrollPosition initial() {
+		return INITIAL;
 	}
 
 	/**
-	 * Creates a new {@link KeysetScrollPosition} from a keyset and {@link Direction}.
+	 * Creates a new {@link KeysetScrollPosition} from a key set 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}.
+	 * @return will never be {@literal null}.
 	 */
-	public static KeysetScrollPosition of(Map<String, ?> keys, Direction direction) {
+	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 keys.isEmpty()
+				? initial()
+				: new KeysetScrollPosition(Collections.unmodifiableMap(new LinkedHashMap<>(keys)), direction);
 	}
 
 	/**
@@ -100,45 +89,78 @@ 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;
+	/**
+	 * Returns whether the current {@link KeysetScrollPosition} scrolls forward.
+	 *
+	 * @return whether the current {@link KeysetScrollPosition} scrolls forward.
+	 */
+	public boolean scrollsForward() {
+		return direction == Direction.FORWARD;
 	}
 
-	@Override
-	public int hashCode() {
+	/**
+	 * Returns whether the current {@link KeysetScrollPosition} scrolls backward.
+	 *
+	 * @return whether the current {@link KeysetScrollPosition} scrolls backward.
+	 */
+	public boolean scrollsBackward() {
+		return direction == Direction.BACKWARD;
+	}
 
-		int result = 17;
+	/**
+	 * Returns a {@link KeysetScrollPosition} based on the same keyset and scrolling forward.
+	 *
+	 * @return will never be {@literal null}.
+	 */
+	public KeysetScrollPosition forward() {
+		return direction == Direction.FORWARD ? this : new KeysetScrollPosition(keys, Direction.FORWARD);
+	}
 
-		result += 31 * ObjectUtils.nullSafeHashCode(keys);
-		result += 31 * ObjectUtils.nullSafeHashCode(direction);
+	/**
+	 * Returns a {@link KeysetScrollPosition} based on the same keyset and scrolling backward.
+	 *
+	 * @return will never be {@literal null}.
+	 */
+	public KeysetScrollPosition backward() {
+		return direction == Direction.BACKWARD ? this : new KeysetScrollPosition(keys, Direction.BACKWARD);
+	}
 
-		return result;
+	/**
+	 * Returns a new {@link KeysetScrollPosition} with the direction reversed.
+	 *
+	 * @return will never be {@literal null}.
+	 */
+	public KeysetScrollPosition reverse() {
+		return new KeysetScrollPosition(keys, direction.reverse());
 	}
 
 	@Override
-	public String toString() {
-		return String.format("KeysetScrollPosition [%s, %s]", direction, keys);
+	public boolean isInitial() {
+		return keys.isEmpty();
 	}
 
-	/**
-	 * Keyset scrolling direction.
-	 */
-	public enum Direction {
+	@Override
+	public boolean equals(@Nullable Object o) {
+
+		if (this == o) {
+			return true;
+		}
 
-		/**
-		 * Forward (default) direction to scroll from the beginning of the results to their end.
-		 */
-		Forward,
+		if (!(o instanceof KeysetScrollPosition that)) {
+			return false;
+		}
+
+		return ObjectUtils.nullSafeEquals(keys, that.keys) //
+				&& direction == that.direction;
+	}
 
-		/**
-		 * Backward direction to scroll from the end of the results to their beginning.
-		 */
-		Backward;
+	@Override
+	public int hashCode() {
+		return Objects.hash(keys, direction);
+	}
+
+	@Override
+	public String toString() {
+		return String.format("KeysetScrollPosition [%s, %s]", direction, keys);
 	}
 }

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

@@ -15,49 +15,54 @@
  */
 package org.springframework.data.domain;
 
+import java.util.Objects;
 import java.util.function.IntFunction;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
-import org.springframework.util.ObjectUtils;
 
 /**
  * A {@link ScrollPosition} based on the offsets within query results.
  *
  * @author Mark Paluch
+ * @author Oliver Drotbohm
  * @since 3.1
  */
 public final class OffsetScrollPosition implements ScrollPosition {
 
-	private static final OffsetScrollPosition initial = new OffsetScrollPosition(0);
+	private static final OffsetScrollPosition INITIAL = new OffsetScrollPosition(0);
 
 	private final long offset;
 
+	/**
+	 * Creates a new {@link OffsetScrollPosition} for the given non-negative offset.
+	 *
+	 * @param offset must be greater or equal to zero.
+	 */
 	private OffsetScrollPosition(long offset) {
+
+		Assert.isTrue(offset >= 0, "Offset must not be negative");
+
 		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.
+	 * @return will never be {@literal null}.
 	 */
-	public static OffsetScrollPosition initial() {
-		return initial;
+	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}.
+	 * @param offset the non-negative offset to start at.
+	 * @return will never be {@literal null}.
 	 */
-	public static OffsetScrollPosition of(long offset) {
-
-		if (offset == 0) {
-			return initial();
-		}
-
-		return new OffsetScrollPosition(offset);
+	static OffsetScrollPosition of(long offset) {
+		return offset == 0 ? initial() : new OffsetScrollPosition(offset);
 	}
 
 	/**
@@ -73,36 +78,51 @@ public static IntFunction<OffsetScrollPosition> positionFunction(long startOffse
 		return startOffset == 0 ? OffsetPositionFunction.ZERO : new OffsetPositionFunction(startOffset);
 	}
 
-	@Override
-	public boolean isInitial() {
-		return offset == 0;
-	}
-
 	/**
+	 * The zero or positive offset.
+	 *
 	 * @return the offset.
 	 */
 	public long getOffset() {
 		return offset;
 	}
 
+	/**
+	 * Returns a new {@link OffsetScrollPosition} that has been advanced by the given value. Negative deltas will be
+	 * constrained so that the new offset is at least zero.
+	 *
+	 * @param delta the value to advance the current offset by.
+	 * @return will never be {@literal null}.
+	 */
+	public OffsetScrollPosition advanceBy(long delta) {
+
+		var value = offset + delta;
+
+		return new OffsetScrollPosition(value < 0 ? 0 : value);
+	}
+
+	@Override
+	public boolean isInitial() {
+		return offset == 0;
+	}
+
 	@Override
-	public boolean equals(Object o) {
-		if (this == o)
+	public boolean equals(@Nullable Object o) {
+
+		if (this == o) {
 			return true;
-		if (o == null || getClass() != o.getClass())
+		}
+
+		if (!(o instanceof OffsetScrollPosition that)) {
 			return false;
-		OffsetScrollPosition that = (OffsetScrollPosition) o;
+		}
+
 		return offset == that.offset;
 	}
 
 	@Override
 	public int hashCode() {
-
-		int result = 17;
-
-		result += 31 * ObjectUtils.nullSafeHashCode(offset);
-
-		return result;
+		return Objects.hash(offset);
 	}
 
 	@Override

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

@@ -174,7 +174,6 @@ default OffsetScrollPosition toScrollPosition() {
 			throw new IllegalStateException("Cannot create OffsetScrollPosition from an unpaged instance");
 		}
 
-		return OffsetScrollPosition.of(getOffset());
+		return ScrollPosition.offset(getOffset());
 	}
-
 }