Collection to Stream without nulls in core-java-collections (#4903)

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<String> collectionAsStream(Collection<String> collection) {
+        return emptyIfNull(collection).stream();
+    }
+}

core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainer.java

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+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<String> collectionAsStream(Collection<String> collection) {
+        return Optional.ofNullable(collection)
+                .map(Collection::stream)
+                .orElseGet(Stream::empty);
+    }
+}

core-java-collections/src/main/java/com/baeldung/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheck.java

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+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<String> collectionAsStream(Collection<String> collection) {
+        return collection == null ? Stream.empty() : collection.stream();
+    }
+
+}