DATACMNS-1637 - Add default stream() method to CloseableIterator.

CloseableIterator now allows construction of a Stream that is associated with a close hook to release resources after its use.

CloseableIterator<Person> iterator = …;

try (Stream<Person> stream = iterator.stream()) {
	assertThat(stream.count()).isEqualTo(3);
}

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

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2020 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.util;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for {@link CloseableIterator}.
+ *
+ * @author Mark Paluch
+ */
+class CloseableIteratorUnitTests {
+
+	@Test // DATACMNS-1637
+	void shouldCreateStream() {
+
+		CloseableIteratorImpl<String> iterator = new CloseableIteratorImpl<>(Arrays.asList("1", "2", "3").iterator());
+
+		List<String> collection = iterator.stream().map(it -> "hello " + it).collect(Collectors.toList());
+
+		assertThat(collection).contains("hello 1", "hello 2", "hello 3");
+		assertThat(iterator.closed).isFalse();
+	}
+
+	@Test // DATACMNS-1637
+	void closeStreamShouldCloseIterator() {
+
+		CloseableIteratorImpl<String> iterator = new CloseableIteratorImpl<>(Arrays.asList("1", "2", "3").iterator());
+
+		try (Stream<String> stream = iterator.stream()) {
+			assertThat(stream.findFirst()).hasValue("1");
+		}
+
+		assertThat(iterator.closed).isTrue();
+	}
+
+	static class CloseableIteratorImpl<T> implements CloseableIterator<T> {
+
+		private final Iterator<T> delegate;
+		private boolean closed = false;
+
+		CloseableIteratorImpl(Iterator<T> delegate) {
+			this.delegate = delegate;
+		}
+
+		@Override
+		public void close() {
+			closed = true;
+		}
+
+		@Override
+		public boolean hasNext() {
+			return delegate.hasNext();
+		}
+
+		@Override
+		public T next() {
+			return delegate.next();
+		}
+	}
+}