From bc8e9cd1597a54150153fb988dd8a9730e819a6c Mon Sep 17 00:00:00 2001
From: VampireAchao <achao1441470436@gmail.com>
Date: Thu, 9 Dec 2021 20:13:39 +0800
Subject: [PATCH] =?UTF-8?q?=E6=96=B0=E5=A2=9ECollStreamUtil.groupKeyValue(?=
 =?UTF-8?q?java.util.Collection<E>,=20java.util.function.Function<E,K>,=20?=
 =?UTF-8?q?java.util.function.Function<E,V>)=EF=BC=8C=E7=94=A8=E4=BA=8E?=
 =?UTF-8?q?=E5=88=86=E7=BB=84=E6=97=B6=E7=9B=B4=E6=8E=A5=E8=8E=B7=E5=8F=96?=
 =?UTF-8?q?=E5=B1=9E=E6=80=A7?=
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---
 .../core/collection/CollStreamUtil.java       | 41 ++++++++++++++++++-
 .../core/collection/CollStreamUtilTest.java   | 20 +++++++++
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/hutool-core/src/main/java/cn/hutool/core/collection/CollStreamUtil.java b/hutool-core/src/main/java/cn/hutool/core/collection/CollStreamUtil.java
index f4ef337eb..09b0257ab 100644
--- a/hutool-core/src/main/java/cn/hutool/core/collection/CollStreamUtil.java
+++ b/hutool-core/src/main/java/cn/hutool/core/collection/CollStreamUtil.java
@@ -13,7 +13,7 @@ import java.util.stream.Collectors;
 /**
  * 集合的stream操作封装
  *
- * @author 528910437@QQ.COM
+ * @author 528910437@QQ.COM VampireAchao<achao1441470436@gmail.com>
  * @since 5.5.2
  */
 public class CollStreamUtil {
@@ -195,6 +195,45 @@ public class CollStreamUtil {
 				.collect(Collectors.groupingBy(key1, Collectors.toMap(key2, Function.identity(), (l, r) -> l)));
 	}
 
+	/**
+	 * 将collection按照规则(比如有相同的班级id)分类成map，map中的key为班级id，value为班级名<br>
+	 * <B>{@code Collection<E> -------> Map<K,List<V>> } </B>
+	 *
+	 * @param collection 需要分类的集合
+	 * @param key        分类的规则
+	 * @param value      分类的规则
+	 * @param <E>        collection中的泛型
+	 * @param <K>        map中的key类型
+	 * @param <V>        List中的value类型
+	 * @return 分类后的map
+	 */
+	public static <E, K, V> Map<K, List<V>> groupKeyValue(Collection<E> collection, Function<E, K> key,
+														  Function<E, V> value) {
+		return groupKeyValue(collection, key, value, false);
+	}
+
+	/**
+	 * 将collection按照规则(比如有相同的班级id)分类成map，map中的key为班级id，value为班级名<br>
+	 * <B>{@code Collection<E> -------> Map<K,List<V>> } </B>
+	 *
+	 * @param collection 需要分类的集合
+	 * @param key        分类的规则
+	 * @param value      分类的规则
+	 * @param isParallel 是否并行流
+	 * @param <E>        collection中的泛型
+	 * @param <K>        map中的key类型
+	 * @param <V>        List中的value类型
+	 * @return 分类后的map
+	 */
+	public static <E, K, V> Map<K, List<V>> groupKeyValue(Collection<E> collection, Function<E, K> key,
+														  Function<E, V> value, boolean isParallel) {
+		if (CollUtil.isEmpty(collection)) {
+			return Collections.emptyMap();
+		}
+		return StreamUtil.of(collection, isParallel)
+				.collect(Collectors.groupingBy(key, Collectors.mapping(value, Collectors.toList())));
+	}
+
 	/**
 	 * 将collection转化为List集合，但是两者的泛型不同<br>
 	 * <B>{@code Collection<E>  ------>  List<T> } </B>
diff --git a/hutool-core/src/test/java/cn/hutool/core/collection/CollStreamUtilTest.java b/hutool-core/src/test/java/cn/hutool/core/collection/CollStreamUtilTest.java
index d5c7df566..f83f82d7f 100644
--- a/hutool-core/src/test/java/cn/hutool/core/collection/CollStreamUtilTest.java
+++ b/hutool-core/src/test/java/cn/hutool/core/collection/CollStreamUtilTest.java
@@ -149,6 +149,26 @@ public class CollStreamUtilTest {
 
 	}
 
+	@Test
+	public void testGroupKeyValue() {
+		Map<Long, List<Long>> map = CollStreamUtil.groupKeyValue(null, Student::getTermId, Student::getClassId);
+		Assert.assertEquals(map, Collections.EMPTY_MAP);
+
+		List<Student> list = new ArrayList<>();
+		map = CollStreamUtil.groupKeyValue(list, Student::getTermId, Student::getClassId);
+		Assert.assertEquals(map, Collections.EMPTY_MAP);
+		list.add(new Student(1, 1, 1, "张三"));
+		list.add(new Student(1, 2, 1, "李四"));
+		list.add(new Student(2, 2, 1, "王五"));
+		map = CollStreamUtil.groupKeyValue(list, Student::getTermId, Student::getClassId);
+
+		Map<Long, List<Long>> compare = new HashMap<>();
+		compare.put(1L, Arrays.asList(1L, 2L));
+		compare.put(2L, Collections.singletonList(2L));
+		Assert.assertEquals(compare, map);
+	}
+
+
 	@Test
 	public void testTranslate2List() {
 		List<String> list = CollStreamUtil.toList(null, Student::getName);