From ee52998f6b95954202f425439dace219a3d40bca Mon Sep 17 00:00:00 2001 From: Felipe Santiago Corro Date: Sun, 5 Aug 2018 14:33:27 -0300 Subject: [PATCH] Collection to Stream without nulls in core-java-collections (#4903) --- ...lectionStreamsUsingCommonsEmptyIfNull.java | 19 ++++++++++ ...ionStreamsUsingJava8OptionalContainer.java | 21 ++++++++++ ...ctionStreamsUsingNullDereferenceCheck.java | 19 ++++++++++ ...treamsUsingCommonsEmptyIfNullUnitTest.java | 37 ++++++++++++++++++ ...msUsingJava8OptionalContainerUnitTest.java | 37 ++++++++++++++++++ ...eamsUsingNullDereferenceCheckUnitTest.java | 38 +++++++++++++++++++ 6 files changed, 171 insertions(+) create mode 100644 core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNull.java create mode 100644 core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainer.java create mode 100644 core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheck.java create mode 100644 core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNullUnitTest.java create mode 100644 core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainerUnitTest.java create mode 100644 core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheckUnitTest.java diff --git a/core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNull.java b/core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNull.java new file mode 100644 index 0000000000..2405c26aac --- /dev/null +++ b/core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNull.java @@ -0,0 +1,19 @@ +package com.baeldung.nullsafecollectionstreams; + +import java.util.Collection; +import java.util.stream.Stream; +import static org.apache.commons.collections4.CollectionUtils.emptyIfNull; + +public class NullSafeCollectionStreamsUsingCommonsEmptyIfNull { + + /** + * This method shows how to make a null safe stream from a collection through the use of + * emptyIfNull() method from Apache Commons CollectionUtils library + * + * @param collection The collection that is to be converted into a stream + * @return The stream that has been created from the collection or an empty stream if the collection is null + */ + public Stream collectionAsStream(Collection collection) { + return emptyIfNull(collection).stream(); + } +} diff --git a/core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainer.java b/core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainer.java new file mode 100644 index 0000000000..da767d4563 --- /dev/null +++ b/core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainer.java @@ -0,0 +1,21 @@ +package com.baeldung.nullsafecollectionstreams; + +import java.util.Collection; +import java.util.Optional; +import java.util.stream.Stream; + +public class NullSafeCollectionStreamsUsingJava8OptionalContainer { + + /** + * This method shows how to make a null safe stream from a collection through the use of + * Java SE 8’s Optional Container + * + * @param collection The collection that is to be converted into a stream + * @return The stream that has been created from the collection or an empty stream if the collection is null + */ + public Stream collectionAsStream(Collection collection) { + return Optional.ofNullable(collection) + .map(Collection::stream) + .orElseGet(Stream::empty); + } +} \ No newline at end of file diff --git a/core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheck.java b/core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheck.java new file mode 100644 index 0000000000..0c10f1cebc --- /dev/null +++ b/core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheck.java @@ -0,0 +1,19 @@ +package com.baeldung.nullsafecollectionstreams; + +import java.util.Collection; +import java.util.stream.Stream; + +public class NullSafeCollectionStreamsUsingNullDereferenceCheck { + + /** + * This method shows how to make a null safe stream from a collection through the use of a check + * to prevent null dereferences + * + * @param collection The collection that is to be converted into a stream + * @return The stream that has been created from the collection or an empty stream if the collection is null + */ + public Stream collectionAsStream(Collection collection) { + return collection == null ? Stream.empty() : collection.stream(); + } + +} diff --git a/core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNullUnitTest.java b/core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNullUnitTest.java new file mode 100644 index 0000000000..875045946d --- /dev/null +++ b/core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNullUnitTest.java @@ -0,0 +1,37 @@ +package com.baeldung.nullsafecollectionstreams; + +import java.util.Arrays; +import java.util.Collection; +import java.util.Iterator; +import java.util.stream.Stream; +import org.junit.Test; +import static org.junit.Assert.*; + +public class NullSafeCollectionStreamsUsingCommonsEmptyIfNullUnitTest { + + private final NullSafeCollectionStreamsUsingCommonsEmptyIfNull instance = + new NullSafeCollectionStreamsUsingCommonsEmptyIfNull(); + @Test + public void whenCollectionIsNull_thenExpectAnEmptyStream() { + Collection collection = null; + Stream expResult = Stream.empty(); + Stream result = instance.collectionAsStream(collection); + assertStreamEquals(expResult, result); + } + + @Test + public void whenCollectionHasElements_thenExpectAStreamOfExactlyTheSameElements() { + Collection collection = Arrays.asList("a", "b", "c"); + Stream expResult = Arrays.stream(new String[] { "a", "b", "c" }); + Stream result = instance.collectionAsStream(collection); + assertStreamEquals(expResult, result); + } + + private static void assertStreamEquals(Stream s1, Stream s2) { + Iterator iter1 = s1.iterator(), iter2 = s2.iterator(); + while (iter1.hasNext() && iter2.hasNext()) + assertEquals(iter1.next(), iter2.next()); + assert !iter1.hasNext() && !iter2.hasNext(); + } + +} diff --git a/core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainerUnitTest.java b/core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainerUnitTest.java new file mode 100644 index 0000000000..402f1a6a19 --- /dev/null +++ b/core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainerUnitTest.java @@ -0,0 +1,37 @@ +package com.baeldung.nullsafecollectionstreams; + +import java.util.Arrays; +import java.util.Collection; +import java.util.Iterator; +import java.util.stream.Stream; +import org.junit.Test; +import static org.junit.Assert.*; + +public class NullSafeCollectionStreamsUsingJava8OptionalContainerUnitTest { + + private final NullSafeCollectionStreamsUsingJava8OptionalContainer instance = + new NullSafeCollectionStreamsUsingJava8OptionalContainer(); + @Test + public void whenCollectionIsNull_thenExpectAnEmptyStream() { + Collection collection = null; + Stream expResult = Stream.empty(); + Stream result = instance.collectionAsStream(collection); + assertStreamEquals(expResult, result); + } + + @Test + public void whenCollectionHasElements_thenExpectAStreamOfExactlyTheSameElements() { + Collection collection = Arrays.asList("a", "b", "c"); + Stream expResult = Arrays.stream(new String[] { "a", "b", "c" }); + Stream result = instance.collectionAsStream(collection); + assertStreamEquals(expResult, result); + } + + private static void assertStreamEquals(Stream s1, Stream s2) { + Iterator iter1 = s1.iterator(), iter2 = s2.iterator(); + while (iter1.hasNext() && iter2.hasNext()) + assertEquals(iter1.next(), iter2.next()); + assert !iter1.hasNext() && !iter2.hasNext(); + } + +} diff --git a/core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheckUnitTest.java b/core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheckUnitTest.java new file mode 100644 index 0000000000..bb6152371d --- /dev/null +++ b/core-java-collections/src/test/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheckUnitTest.java @@ -0,0 +1,38 @@ +package com.baeldung.nullsafecollectionstreams; + +import java.util.Arrays; +import java.util.Collection; +import java.util.Iterator; +import java.util.stream.Stream; +import org.junit.Test; +import static org.junit.Assert.*; + +public class NullSafeCollectionStreamsUsingNullDereferenceCheckUnitTest { + + private final NullSafeCollectionStreamsUsingNullDereferenceCheck instance = + new NullSafeCollectionStreamsUsingNullDereferenceCheck(); + + @Test + public void whenCollectionIsNull_thenExpectAnEmptyStream() { + Collection collection = null; + Stream expResult = Stream.empty(); + Stream result = instance.collectionAsStream(collection); + assertStreamEquals(expResult, result); + } + + @Test + public void whenCollectionHasElements_thenExpectAStreamOfExactlyTheSameElements() { + Collection collection = Arrays.asList("a", "b", "c"); + Stream expResult = Arrays.stream(new String[] { "a", "b", "c" }); + Stream result = instance.collectionAsStream(collection); + assertStreamEquals(expResult, result); + } + + private static void assertStreamEquals(Stream s1, Stream s2) { + Iterator iter1 = s1.iterator(), iter2 = s2.iterator(); + while (iter1.hasNext() && iter2.hasNext()) + assertEquals(iter1.next(), iter2.next()); + assert !iter1.hasNext() && !iter2.hasNext(); + } + +}