Fix spliterator size hint in CloseableIterator.spliterator().

We now report -1 as size to avoid zero-size results for count() or toList() operators.

Closes #2519

Author: mp911de

Diff for: src/main/java/org/springframework/data/util/CloseableIterator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015-2021 the original author or authors.
+ * Copyright 2015-2022 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.
@@ -49,12 +49,14 @@ public interface CloseableIterator<T> extends Iterator<T>, Closeable {
 	 * The default implementation should be overridden by subclasses that can return a more efficient spliterator. To
 	 * preserve expected laziness behavior for the {@link #stream()} method, spliterators should either have the
 	 * characteristic of {@code IMMUTABLE} or {@code CONCURRENT}, or be late-binding.
+	 * <p>
+	 * The default implementation does not report a size.
 	 *
 	 * @return a {@link Spliterator} over the elements in this {@link Iterator}.
 	 * @since 2.4
 	 */
 	default Spliterator<T> spliterator() {
-		return Spliterators.spliterator(this, 0, 0);
+		return Spliterators.spliterator(this, -1, 0);
 	}
 
 	/**

Diff for: src/test/java/org/springframework/data/util/CloseableIteratorUnitTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2021 the original author or authors.
+ * Copyright 2020-2022 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.
@@ -33,18 +33,38 @@ class CloseableIteratorUnitTests {
 	@Test // DATACMNS-1637
 	void shouldCreateStream() {
 
-		var iterator = new CloseableIteratorImpl<String>(Arrays.asList("1", "2", "3").iterator());
+		var iterator = new CloseableIteratorImpl<>(Arrays.asList("1", "2", "3").iterator());
 
 		var collection = iterator.stream().map(it -> "hello " + it).collect(Collectors.toList());
 
 		assertThat(collection).contains("hello 1", "hello 2", "hello 3");
 		assertThat(iterator.closed).isFalse();
 	}
 
+	@Test // GH-2519
+	void shouldCount() {
+
+		var iterator = new CloseableIteratorImpl<>(Arrays.asList("1", "2", "3").iterator());
+
+		var count = iterator.stream().count();
+
+		assertThat(count).isEqualTo(3);
+	}
+
+	@Test // GH-2519
+	void shouldApplyToList() {
+
+		var iterator = new CloseableIteratorImpl<>(Arrays.asList("1", "2", "3").iterator());
+
+		var list = iterator.stream().toList();
+
+		assertThat(list).isEqualTo(Arrays.asList("1", "2", "3"));
+	}
+
 	@Test // DATACMNS-1637
 	void closeStreamShouldCloseIterator() {
 
-		var iterator = new CloseableIteratorImpl<String>(Arrays.asList("1", "2", "3").iterator());
+		var iterator = new CloseableIteratorImpl<>(Arrays.asList("1", "2", "3").iterator());
 
 		try (var stream = iterator.stream()) {
 			assertThat(stream.findFirst()).hasValue("1");