Merge pull request #937 from GRain-long/patch-1

[新特性]添加intersectionDistinct方法

hutool-core/src/main/java/cn/hutool/core/collection/CollUtil.java

@@ -266,6 +266,39 @@ public class CollUtil {
 		}
 		return intersection;
 	}
+	
+	/**
+	 * 多个集合的交集<br>
+	 * 针对一个集合中存在多个相同元素的情况，只保留一个<br>
+	 * 例如：集合1：[a, b, c, c, c]，集合2：[a, b, c, c]<br>
+	 * 结果：[a, b, c]，此结果中只保留了一个c
+	 *
+	 * @param <T>        集合元素类型
+	 * @param coll1      集合1
+	 * @param coll2      集合2
+	 * @param otherColls 其它集合
+	 * @return 并集的集合，返回 {@link LinkedHashSet}
+	 */
+	@SafeVarargs
+	public static <T> Set<T> intersectionDistinct(Collection<T> coll1, Collection<T> coll2, Collection<T>... otherColls) {
+		final Set<T> result;
+		if (isEmpty(coll1)) {
+			result = new LinkedHashSet<>();
+		} else {
+			result = new LinkedHashSet<>(coll1);
+		}
+
+		if (isNotEmpty(coll2)) {
+			result.retainAll(coll2);
+		}
+
+		if (ArrayUtil.isNotEmpty(otherColls)) {
+			for (Collection<T> otherColl : otherColls) {
+				result.retainAll(otherColl);
+			}
+		}
+		return result;
+	}
 
 	/**
 	 * 两个集合的差集<br>

hutool-core/src/test/java/cn/hutool/core/collection/CollUtilTest.java

@@ -76,8 +76,21 @@ public class CollUtilTest {
 		ArrayList<String> list1 = CollUtil.newArrayList("a", "b", "b", "c", "d", "x");
 		ArrayList<String> list2 = CollUtil.newArrayList("a", "b", "b", "b", "c", "d");
 
-		Collection<String> union = CollUtil.intersection(list1, list2);
-		Assert.assertEquals(2, CollUtil.count(union, t -> t.equals("b")));
+		Collection<String> intersection = CollUtil.intersection(list1, list2);
+		Assert.assertEquals(2, CollUtil.count(intersection, t -> t.equals("b")));
+	}
+	
+	@Test
+	public void intersectionTest2() {
+		ArrayList<String> list1 = CollUtil.newArrayList("a", "b", "b", "c", "d", "x");
+		ArrayList<String> list2 = CollUtil.newArrayList("a", "b", "b", "b", "c", "d");
+		ArrayList<String> list3 = CollUtil.newArrayList();
+
+		Collection<String> intersectionDistinct = CollUtil.intersectionDistinct(list1, list2);
+        	Assert.assertEquals(CollUtil.newLinkedHashSet("a", "b", "c", "d"), intersectionDistinct);
+
+        	Collection<String> intersectionDistinct2 = CollUtil.intersectionDistinct(list1, list2, list3);
+        	Assert.assertTrue(intersectionDistinct2.isEmpty());
 	}
 
 	@Test