From 8c75a92b246dfe001caae71ed8263901ac448152 Mon Sep 17 00:00:00 2001
From: Oliver Drotbohm <ogierke@pivotal.io>
Date: Mon, 28 Jan 2019 11:03:05 +0100
Subject: [PATCH] =?UTF-8?q?DATACMNS-1476=20-=20Added=20Slice.nextOrLastPag?=
 =?UTF-8?q?eable()=20and=20=E2=80=A6.previousOrFirstPageable().?=
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We now expose methods that allow to traverse the Pageables but make sure we stay within the result bounds.

Related ticket: DATACMNS-1475.
---
 .../springframework/data/domain/Slice.java    | 24 +++++++++++++++++++
 .../data/domain/PageImplUnitTests.java        | 13 ++++++++++
 2 files changed, 37 insertions(+)

diff --git a/src/main/java/org/springframework/data/domain/Slice.java b/src/main/java/org/springframework/data/domain/Slice.java
index e4f73bbd7..9052d029e 100644
--- a/src/main/java/org/springframework/data/domain/Slice.java
+++ b/src/main/java/org/springframework/data/domain/Slice.java
@@ -115,6 +115,7 @@ public interface Slice<T> extends Streamable<T> {
 	 * current {@link Slice} is already the last one. Clients should check {@link #hasNext()} before calling this method.
 	 *
 	 * @return
+	 * @see #nextOrLastPageable()
 	 */
 	Pageable nextPageable();
 
@@ -124,6 +125,7 @@ public interface Slice<T> extends Streamable<T> {
 	 * method.
 	 *
 	 * @return
+	 * @see #previousPageable()
 	 */
 	Pageable previousPageable();
 
@@ -135,4 +137,26 @@ public interface Slice<T> extends Streamable<T> {
 	 * @since 1.10
 	 */
 	<U> Slice<U> map(Function<? super T, ? extends U> converter);
+
+	/**
+	 * Returns the {@link Pageable} describing the next slice or the one describing the current slice in case it's the
+	 * last one.
+	 *
+	 * @return
+	 * @since 2.2
+	 */
+	default Pageable nextOrLastPageable() {
+		return hasNext() ? nextPageable() : getPageable();
+	}
+
+	/**
+	 * Returns the {@link Pageable} describing the previous slice or the one describing the current slice in case it's the
+	 * first one.
+	 *
+	 * @return
+	 * @since 2.2
+	 */
+	default Pageable previousOrFirstPageable() {
+		return hasPrevious() ? previousPageable() : getPageable();
+	}
 }
diff --git a/src/test/java/org/springframework/data/domain/PageImplUnitTests.java b/src/test/java/org/springframework/data/domain/PageImplUnitTests.java
index 5416b3ba3..27e37cc3b 100755
--- a/src/test/java/org/springframework/data/domain/PageImplUnitTests.java
+++ b/src/test/java/org/springframework/data/domain/PageImplUnitTests.java
@@ -161,4 +161,17 @@ public class PageImplUnitTests {
 		assertThat(new PageImpl<>(Collections.<String> emptyList(), PageRequest.of(1, 10), 0).getTotalElements())
 				.isEqualTo(0L);
 	}
+
+	@Test // DATACMNS-1476
+	public void returnsSelfPagablesIfThePageIsAlreadyTheFirstOrLastOne() {
+
+		Pageable pageable = PageRequest.of(0, 2);
+		Slice<String> page = new PageImpl<>(Arrays.asList("foo", "bar"), pageable, 2);
+
+		assertThat(page.previousPageable()).isEqualTo(Pageable.unpaged());
+		assertThat(page.previousOrFirstPageable()).isEqualTo(pageable);
+
+		assertThat(page.nextPageable()).isEqualTo(Pageable.unpaged());
+		assertThat(page.nextOrLastPageable()).isEqualTo(pageable);
+	}
 }