Add Streams.of(Enumeration<E>)

3 files changed, 74 insertions, 0 deletions

diff --git a/src/changes/changes.xml b/src/changes/changes.xml
index 454d5690a..e5e32ada0 100644
--- a/src/changes/changes.xml
+++ b/src/changes/changes.xml
@@ -157,6 +157,7 @@ The <action> type attribute can be add,update,fix,remove.
     <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add SystemUtils.IS_JAVA_18.</action>
     <action issue="LANG-1627" type="add" dev="ggregory" due-to="Alberto Scotto, Avijit Chakraborty, Steve Bosman, Bruno P. Kinoshita, Gary Gregory">Add ArrayUtils.oneHot().</action>
     <action issue="LANG-1662" type="add" dev="ggregory" due-to="Daniel Augusto Veronezi Salvador, Gary Gregory, Bruno P. Kinoshita">Let ReflectionToStringBuilder only reflect given field names #849.</action>
+    <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add Streams.of(Enumeration&lt;E&gt;).</action>
     <!-- UPDATE -->
     <action                   type="update" dev="ggregory" due-to="Dependabot, XenoAmess, Gary Gregory">Bump actions/cache from 2.1.4 to 3.0.5 #742, #752, #764, #833, #867.</action>
     <action                   type="update" dev="ggregory" due-to="Dependabot">Bump actions/checkout from 2 to 3 #819, #825, #859.</action>
diff --git a/src/main/java/org/apache/commons/lang3/stream/Streams.java b/src/main/java/org/apache/commons/lang3/stream/Streams.java
index e44ed7bf0..720405129 100644
--- a/src/main/java/org/apache/commons/lang3/stream/Streams.java
+++ b/src/main/java/org/apache/commons/lang3/stream/Streams.java
@@ -19,9 +19,12 @@ package org.apache.commons.lang3.stream;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.Enumeration;
 import java.util.List;
 import java.util.Objects;
 import java.util.Set;
+import java.util.Spliterator;
+import java.util.Spliterators.AbstractSpliterator;
 import java.util.function.BiConsumer;
 import java.util.function.BinaryOperator;
 import java.util.function.Consumer;
@@ -31,6 +34,7 @@ import java.util.function.Supplier;
 import java.util.stream.Collector;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
 
 import org.apache.commons.lang3.ArrayUtils;
 import org.apache.commons.lang3.function.Failable;
@@ -123,6 +127,47 @@ public class Streams {
     }
 
     /**
+     * Helps implement {@link Streams#of(Enumeration)}.
+     *
+     * @param <T> The element type.
+     */
+    private static class EnumerationSpliterator<T> extends AbstractSpliterator<T> {
+
+        private final Enumeration<T> enumeration;
+
+        /**
+         * Creates a spliterator reporting the given estimated size and additionalCharacteristics.
+         *
+         * @param estimatedSize the estimated size of this spliterator if known, otherwise {@code Long.MAX_VALUE}.
+         * @param additionalCharacteristics properties of this spliterator's source or elements. If {@code SIZED} is reported then this spliterator will
+         *        additionally report {@code SUBSIZED}.
+         * @param enumeration The Enumeration to wrap.
+         */
+        protected EnumerationSpliterator(final long estimatedSize, final int additionalCharacteristics, final Enumeration<T> enumeration) {
+            super(estimatedSize, additionalCharacteristics);
+            this.enumeration = Objects.requireNonNull(enumeration, "enumeration");
+        }
+
+        @Override
+        public void forEachRemaining(final Consumer<? super T> action) {
+            while (enumeration.hasMoreElements()) {
+                next(action);
+            }
+        }
+
+        private boolean next(final Consumer<? super T> action) {
+            action.accept(enumeration.nextElement());
+            return true;
+
+        }
+
+        @Override
+        public boolean tryAdvance(final Consumer<? super T> action) {
+            return enumeration.hasMoreElements() ? next(action) : false;
+        }
+    }
+
+    /**
      * A reduced, and simplified version of a {@link Stream} with failable method signatures.
      *
      * @param <T> The streams element type.
@@ -573,6 +618,18 @@ public class Streams {
     }
 
     /**
+     * Streams the elements of the given enumeration in order.
+     *
+     * @param <E> The enumeration element type.
+     * @param enumeration The enumeration to stream.
+     * @return a new stream.
+     * @since 3.13.0
+     */
+    public static <E> Stream<E> of(final Enumeration<E> enumeration) {
+        return StreamSupport.stream(new EnumerationSpliterator<>(Long.MAX_VALUE, Spliterator.ORDERED, enumeration), false);
+    }
+
+    /**
      * Null-safe version of {@link Stream#of(Object[])}.
      *
      * @param <T> the type of stream elements.
diff --git a/src/test/java/org/apache/commons/lang3/stream/StreamsTest.java b/src/test/java/org/apache/commons/lang3/stream/StreamsTest.java
index 625bff4cb..99b34204b 100644
--- a/src/test/java/org/apache/commons/lang3/stream/StreamsTest.java
+++ b/src/test/java/org/apache/commons/lang3/stream/StreamsTest.java
@@ -24,11 +24,13 @@ import static org.junit.jupiter.api.Assertions.assertAll;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.DynamicTest.dynamicTest;
 
 import java.lang.reflect.UndeclaredThrowableException;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Hashtable;
 import java.util.List;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -162,6 +164,20 @@ public class StreamsTest extends AbstractLangTest {
     }
 
     @Test
+    public void testOfEnumeration() {
+        final Hashtable<String, Integer> table = new Hashtable<>();
+        assertEquals(0, Streams.of(table.elements()).count());
+        table.put("One", 1);
+        assertEquals(1, Streams.of(table.elements()).count());
+        table.put("Two", 2);
+        assertEquals(2, Streams.of(table.elements()).count());
+        final List<String> collect = Streams.of(table.keys()).collect(Collectors.toList());
+        assertTrue(collect.contains("One"));
+        assertTrue(collect.contains("Two"));
+        assertEquals(2, collect.size());
+    }
+
+    @Test
     public void testSimpleStreamFilter() {
         final List<String> input = Arrays.asList("1", "2", "3", "4", "5", "6");
         final List<Integer> output = Failable.stream(input).map(Integer::valueOf).filter(i -> (i.intValue() % 2 == 0)).collect(Collectors.toList());