OAK-11573: add size api in IteratorUtils (#2159)

Author: t-rana

oak-commons/src/main/java/org/apache/jackrabbit/oak/commons/collections/IteratorUtils.java

@@ -177,4 +177,17 @@ public static boolean elementsEqual(final Iterator<?> iterator1, final Iterator<
         // return true if both the iterators have same number of elements
         return !iterator1.hasNext() && !iterator2.hasNext();
     }
+
+    /**
+     * Returns the number of elements in the given iterator.
+     * <p>
+     * This method consumes the iterator to count the elements.
+     * A null or empty iterator returns 0.
+     *
+     * @param iterator the iterator whose size is to be determined
+     * @return the number of elements in the iterator
+     */
+    public static int size(Iterator<?> iterator) {
+        return org.apache.commons.collections4.IteratorUtils.size(iterator);
+    }
 }

oak-commons/src/test/java/org/apache/jackrabbit/oak/commons/collections/IteratorUtilsTest.java

@@ -231,4 +231,59 @@ public void testLargeIterators() {
         list2.set(9999, -1);
         Assert.assertFalse(IteratorUtils.elementsEqual(list1.iterator(), list2.iterator()));
     }
+
+    @Test
+    public void testSizeWithMultipleElements() {
+        List<String> list = Arrays.asList("one", "two", "three", "four", "five");
+        Iterator<String> iterator = list.iterator();
+        Assert.assertEquals(5, IteratorUtils.size(iterator));
+        Assert.assertFalse("Iterator should be consumed after size operation", iterator.hasNext());
+    }
+
+    @Test
+    public void testSizeWithEmptyIterator() {
+        Assert.assertEquals(0, IteratorUtils.size(Collections.emptyIterator()));
+    }
+
+    @Test
+    public void testSizeWithNullIterator() {
+        Assert.assertEquals(0,IteratorUtils.size(null));
+    }
+
+    @Test
+    public void testSizeConsumesIterator() {
+        List<String> list = Arrays.asList("one", "two", "three");
+        Iterator<String> iterator = list.iterator();
+
+        Assert.assertEquals(3, IteratorUtils.size(iterator));
+        Assert.assertFalse("Iterator should be consumed after size operation", iterator.hasNext());
+    }
+
+    @Test
+    public void testSizeWithSingleElement() {
+        List<String> singletonList = Collections.singletonList("single");
+        Assert.assertEquals(1, IteratorUtils.size(singletonList.iterator()));
+    }
+
+    @Test
+    public void testSizeWithCustomIterator() {
+        Iterator<Integer> customIterator = new Iterator<>() {
+            private int count = 0;
+
+            @Override
+            public boolean hasNext() {
+                return count < 10;
+            }
+
+            @Override
+            public Integer next() {
+                if (!hasNext()) {
+                    throw new NoSuchElementException();
+                }
+                return count++;
+            }
+        };
+        Assert.assertEquals(10, IteratorUtils.size(customIterator));
+        Assert.assertFalse("Iterator should be consumed after size operation", customIterator.hasNext());
+    }
 }