From a1dba4f36bb85e6f0eb49a2a9835c5f84845f603 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=A4=A7=E7=81=AByzs?= <835476090@qq.com>
Date: Tue, 4 May 2021 15:01:43 +0800
Subject: [PATCH] =?UTF-8?q?ListUtil=E7=B1=BB=E6=B7=BB=E5=8A=A0countMap?=
 =?UTF-8?q?=E6=96=B9=E6=B3=95=E2=9C=92=EF=B8=8F?=
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---
 .../cn/hutool/core/collection/ListUtil.java   | 37 +++++++++++++++----
 .../hutool/core/collection/ListUtilTest.java  | 22 +++++++++++
 2 files changed, 51 insertions(+), 8 deletions(-)

diff --git a/hutool-core/src/main/java/cn/hutool/core/collection/ListUtil.java b/hutool-core/src/main/java/cn/hutool/core/collection/ListUtil.java
index 088e19787..d6a3093d2 100644
--- a/hutool-core/src/main/java/cn/hutool/core/collection/ListUtil.java
+++ b/hutool-core/src/main/java/cn/hutool/core/collection/ListUtil.java
@@ -5,18 +5,12 @@ import cn.hutool.core.comparator.PropertyComparator;
 import cn.hutool.core.convert.Convert;
 import cn.hutool.core.lang.Editor;
 import cn.hutool.core.lang.Matcher;
+import cn.hutool.core.map.MapUtil;
 import cn.hutool.core.util.ArrayUtil;
 import cn.hutool.core.util.ObjectUtil;
 import cn.hutool.core.util.PageUtil;
 
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.Comparator;
-import java.util.Enumeration;
-import java.util.Iterator;
-import java.util.LinkedList;
-import java.util.List;
+import java.util.*;
 import java.util.concurrent.CopyOnWriteArrayList;
 
 public class ListUtil {
@@ -450,6 +444,33 @@ public class ListUtil {
 		return list2;
 	}
 
+	/**
+	 * 统计list中元素出现次数
+	 *
+	 * @param list list容器
+	 * @return Map<T, Long>    统计次数 如: {"hello":10}
+	 * @since 5.6.5
+	 */
+	public static <T> Map<T, Long> countMap(List<T> list) {
+		Map<T, Long> countMap = MapUtil.newHashMap();
+		for (T o : list) {
+			countMap.put(o, countMap.getOrDefault(o, 0L) + 1);
+		}
+		return countMap;
+		//return list.stream().collect(Collectors.groupingBy(o -> o, Collectors.counting()));//stream方式
+	}
+
+	/**
+	 * 统计list中元素出现次数
+	 *
+	 * @param list list容器
+	 * @return Map<T, Long>    统计次数 如: {"hello":10}
+	 * @since 5.6.5
+	 */
+	public static <T> Map<T, Long> countMap(List<T> list, boolean isValueDesc) {
+		return MapUtil.sortByValue(countMap(list), isValueDesc);
+	}
+
 	/**
 	 * 获取匹配规则定义中匹配到元素的所有位置
 	 *
diff --git a/hutool-core/src/test/java/cn/hutool/core/collection/ListUtilTest.java b/hutool-core/src/test/java/cn/hutool/core/collection/ListUtilTest.java
index 46c94cdd5..17f413a0a 100644
--- a/hutool-core/src/test/java/cn/hutool/core/collection/ListUtilTest.java
+++ b/hutool-core/src/test/java/cn/hutool/core/collection/ListUtilTest.java
@@ -10,6 +10,7 @@ import org.junit.Test;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Map;
 
 public class ListUtilTest {
 
@@ -46,6 +47,27 @@ public class ListUtilTest {
 		Assert.assertEquals("edit3", filter.get(2));
 	}
 
+	@Test
+	@Ignore
+	public void countMapTest(){
+		List<String> list = new ArrayList<>();
+		list.add("AAA");
+		list.add("BBB");
+		list.add("AAA");
+		list.add("CCC");
+		list.add("DDD");
+		list.add("DDD");
+		//统计不排序
+		Map<?, Long> countMap = ListUtil.countMap(list);
+		Console.log(countMap);
+		//统计倒序排列
+		Map<String, Long> descCountMap = ListUtil.countMap(list, Boolean.TRUE);
+		Console.log(descCountMap);
+		//统计正序排列
+		Map<String, Long> ascCountMap= ListUtil.countMap(list, Boolean.FALSE);
+		Console.log(ascCountMap);
+	}
+
 	@Test
 	public void indexOfAll() {
 		List<String> a = ListUtil.toLinkedList("1", "2", "3", "4", "3", "2", "1");