From 0b8c4bbad02b280a22115c8b383a288b77eda887 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E9=9D=92=E9=9F=B5?= <1320162752@qq.com>
Date: Mon, 26 Sep 2022 21:33:49 +0800
Subject: [PATCH] =?UTF-8?q?CollUtil.unionAll=E4=BC=98=E5=8C=96=EF=BC=9A?=
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---
 .../cn/hutool/core/collection/CollUtil.java   | 42 ++++++++++------
 .../hutool/core/collection/CollUtilTest.java  | 48 +++++++++++++++++++
 2 files changed, 75 insertions(+), 15 deletions(-)

diff --git a/hutool-core/src/main/java/cn/hutool/core/collection/CollUtil.java b/hutool-core/src/main/java/cn/hutool/core/collection/CollUtil.java
index 977dbcd87..ba1b99b23 100755
--- a/hutool-core/src/main/java/cn/hutool/core/collection/CollUtil.java
+++ b/hutool-core/src/main/java/cn/hutool/core/collection/CollUtil.java
@@ -207,27 +207,39 @@ public class CollUtil {
 	 */
 	@SafeVarargs
 	public static <T> List<T> unionAll(Collection<T> coll1, Collection<T> coll2, Collection<T>... otherColls) {
-		final List<T> result;
-		if (isEmpty(coll1)) {
-			result = new ArrayList<>();
-		} else {
-			result = new ArrayList<>(coll1);
+		if (CollUtil.isEmpty(coll1) && CollUtil.isEmpty(coll2) && ArrayUtil.isEmpty(otherColls)) {
+			return Collections.emptyList();
 		}
 
-		if (isNotEmpty(coll2)) {
-			result.addAll(coll2);
-		}
-
-		if (ArrayUtil.isNotEmpty(otherColls)) {
+		// 计算元素总数
+		int totalSize = 0;
+		totalSize += size(coll1);
+		totalSize += size(coll2);
+		if (otherColls != null) {
 			for (Collection<T> otherColl : otherColls) {
-				if (isEmpty(otherColl)) {
-					continue;
-				}
-				result.addAll(otherColl);
+				totalSize += size(otherColl);
 			}
 		}
 
-		return result;
+		// 根据size创建，防止多次扩容
+		List<T> res = new ArrayList<>(totalSize);
+		if (coll1 != null) {
+			res.addAll(coll1);
+		}
+		if (coll2 != null) {
+			res.addAll(coll2);
+		}
+		if (otherColls == null) {
+			return res;
+		}
+
+		for (Collection<T> otherColl : otherColls) {
+			if (otherColl != null) {
+				res.addAll(otherColl);
+			}
+		}
+
+		return res;
 	}
 
 	/**
diff --git a/hutool-core/src/test/java/cn/hutool/core/collection/CollUtilTest.java b/hutool-core/src/test/java/cn/hutool/core/collection/CollUtilTest.java
index 68883a538..6ff5c4339 100755
--- a/hutool-core/src/test/java/cn/hutool/core/collection/CollUtilTest.java
+++ b/hutool-core/src/test/java/cn/hutool/core/collection/CollUtilTest.java
@@ -940,6 +940,54 @@ public class CollUtilTest {
 		final List<String> list3 = null;
 		final List<String> list = CollUtil.unionAll(list1, list2, list3);
 		Assert.assertNotNull(list);
+
+		final List<String> resList2 = CollUtil.unionAll(null, null, null);
+		Assert.assertNotNull(resList2);
+	}
+
+	@Test
+	public void unionAllOrdinaryTest() {
+		final List<Integer> list1 = CollectionUtil.newArrayList(1, 2, 2, 3, 3);
+		final List<Integer> list2 = CollectionUtil.newArrayList(1, 2, 3);
+		final List<Integer> list3 = CollectionUtil.newArrayList(4, 5, 6);
+		final List<Integer> list = CollUtil.unionAll(list1, list2, list3);
+		Assert.assertNotNull(list);
+		Assert.assertArrayEquals(
+				CollectionUtil.newArrayList(1, 2, 2, 3, 3, 1, 2, 3, 4, 5, 6).toArray(),
+				list.toArray());
+	}
+
+	@Test
+	public void unionAllTwoOrdinaryTest() {
+		final List<Integer> list1 = CollectionUtil.newArrayList(1, 2, 2, 3, 3);
+		final List<Integer> list2 = CollectionUtil.newArrayList(1, 2, 3);
+		final List<Integer> list = CollUtil.unionAll(list1, list2);
+		Assert.assertNotNull(list);
+		Assert.assertArrayEquals(
+				CollectionUtil.newArrayList(1, 2, 2, 3, 3, 1, 2, 3).toArray(),
+				list.toArray());
+	}
+
+	@Test
+	public void unionAllOtherIsNullTest() {
+		final List<Integer> list1 = CollectionUtil.newArrayList(1, 2, 2, 3, 3);
+		final List<Integer> list2 = CollectionUtil.newArrayList(1, 2, 3);
+		final List<Integer> list = CollUtil.unionAll(list1, list2, null);
+		Assert.assertNotNull(list);
+		Assert.assertArrayEquals(
+				CollectionUtil.newArrayList(1, 2, 2, 3, 3, 1, 2, 3).toArray(),
+				list.toArray());
+	}
+
+	@Test
+	public void unionAllOtherTwoNullTest() {
+		final List<Integer> list1 = CollectionUtil.newArrayList(1, 2, 2, 3, 3);
+		final List<Integer> list2 = CollectionUtil.newArrayList(1, 2, 3);
+		final List<Integer> list = CollUtil.unionAll(list1, list2, null, null);
+		Assert.assertNotNull(list);
+		Assert.assertArrayEquals(
+				CollectionUtil.newArrayList(1, 2, 2, 3, 3, 1, 2, 3).toArray(),
+				list.toArray());
 	}
 
 	@Test