DATAGEODE-302 - Add 'nullSafeStream(:Stream)' utility method to StreamUtils.

spring-data-geode/src/main/java/org/springframework/data/gemfire/util/StreamUtils.java

@@ -13,7 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.data.gemfire.util;
 
 import static org.springframework.data.gemfire.util.ArrayUtils.nullSafeArray;
@@ -48,4 +47,16 @@ public abstract class StreamUtils {
 
 		return concatenatedStream;
 	}
+
+	/**
+	 * Utility method used to guard against {@literal null} {@link Stream Streams}.
+	 *
+	 * @param <T> {@link Class type} of the {@link Object elements} in the {@link Stream}.
+	 * @param stream {@link Stream} to evaluate.
+	 * @return the given {@link Stream} if not {@literal null} or an {@link Stream#empty() empty} {@link Stream}.
+	 * @see java.util.stream.Stream
+	 */
+	public static <T> Stream<T> nullSafeStream(Stream<T> stream) {
+		return stream != null ? stream : Stream.empty();
+	}
 }

spring-data-geode/src/test/java/org/springframework/data/gemfire/util/StreamUtilsTests.java

@@ -13,10 +13,10 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.data.gemfire.util;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
 
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -24,11 +24,12 @@ import java.util.stream.Stream;
 import org.junit.Test;
 
 /**
- * Unit tests for {@link StreamUtils}.
+ * Unit Tests for {@link StreamUtils}.
  *
  * @author John Blum
  * @see java.util.stream.Stream
  * @see org.junit.Test
+ * @see org.mockito.Mockito
  * @see org.springframework.data.gemfire.util.StreamUtils
  * @since 2.0.0
  */
@@ -74,4 +75,17 @@ public class StreamUtilsTests {
 		assertThat(stream).isNotNull();
 		assertThat(stream.collect(Collectors.toList())).containsExactly(1, 2, 3, 4, 5, 6, 7, 8, 9);
 	}
+
+	@Test
+	public void nullSafeStreamWithStream() {
+
+		Stream<?> mockStream = mock(Stream.class);
+
+		assertThat(StreamUtils.nullSafeStream(mockStream)).isSameAs(mockStream);
+	}
+
+	@Test
+	public void nullSafeStreamWithNull() {
+		assertThat(StreamUtils.nullSafeStream(null)).isEqualTo(Stream.empty());
+	}
 }

spring-data-geode/src/test/java/org/springframework/data/gemfire/util/StreamUtilsUnitTests.java

@@ -0,0 +1,95 @@
+/*
+ * Copyright 2017-2020 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.gemfire.util;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import org.junit.Test;
+
+/**
+ * Unit Tests for {@link StreamUtils}.
+ *
+ * @author John Blum
+ * @see java.util.stream.Stream
+ * @see org.junit.Test
+ * @see org.mockito.Mockito
+ * @see org.springframework.data.gemfire.util.StreamUtils
+ * @since 2.0.0
+ */
+public class StreamUtilsUnitTests {
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void concatNoStreams() {
+
+		Stream<Object> stream = StreamUtils.concat();
+
+		assertThat(stream).isNotNull();
+		assertThat(stream.count()).isEqualTo(0);
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void concatOneStream() {
+
+		Stream<Integer> stream = StreamUtils.concat(Stream.of(1, 2, 3));
+
+		assertThat(stream).isNotNull();
+		assertThat(stream.collect(Collectors.toList())).containsExactly(1, 2, 3);
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void concatTwoStreams() {
+
+		Stream<Integer> stream = StreamUtils.concat(Stream.of(1, 2, 3), Stream.of(4, 5, 6));
+
+		assertThat(stream).isNotNull();
+		assertThat(stream.collect(Collectors.toList())).containsExactly(1, 2, 3, 4, 5, 6);
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void concatThreeStreams() {
+
+		Stream<Integer> stream =
+			StreamUtils.concat(Stream.of(1, 2, 3), Stream.of(4, 5, 6), Stream.of(7, 8, 9));
+
+		assertThat(stream).isNotNull();
+		assertThat(stream.collect(Collectors.toList())).containsExactly(1, 2, 3, 4, 5, 6, 7, 8, 9);
+	}
+
+	@Test
+	public void nullSafeStreamWithStream() {
+
+		Stream<?> mockStream = mock(Stream.class);
+
+		assertThat(StreamUtils.nullSafeStream(mockStream)).isSameAs(mockStream);
+	}
+
+	@Test
+	public void nullSafeStreamWithNull() {
+
+		Stream<?> stream = StreamUtils.nullSafeStream(null);
+
+		assertThat(stream).isNotNull();
+		assertThat(stream.count()).isZero();
+	}
+}