新增MapUtil#change函数

hutool-core/src/main/java/cn/hutool/core/map/MapUtil.java

@@ -27,6 +27,8 @@ import java.util.Set;
 import java.util.SortedMap;
 import java.util.TreeMap;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.stream.Collectors;
+import java.util.function.BiFunction;
 
 /**
  * Map相关工具类
@@ -548,7 +550,7 @@ public class MapUtil {
 	 * @since 5.0.4
 	 */
 	public static String sortJoin(Map<?, ?> params, String separator, String keyValueSeparator, boolean isIgnoreNull,
-								  String... otherParams) {
+	                              String... otherParams) {
 		return join(sort(params), separator, keyValueSeparator, isIgnoreNull, otherParams);
 	}
 
@@ -668,6 +670,25 @@ public class MapUtil {
 		return edit(map, t -> filter.accept(t) ? t : null);
 	}
 
+
+	/**
+	 * 变更<br>
+	 * 变更过程通过传入的 {@link BiFunction} 实现来返回一个值可以为不同类型的 {@link Map}
+	 *
+	 * @param map        原有的map
+	 * @param biFunction {@code lambda}，参数包含{@code key},{@code value}，返回值会作为新的{@code value}
+	 * @param <K>        {@code key}的类型
+	 * @param <V>        {@code value}的类型
+	 * @param <R>        新的，修改后的{@code value}的类型
+	 * @return 值可以为不同类型的 {@link Map}
+	 */
+	public static <K, V, R> Map<K, R> change(Map<K, V> map, BiFunction<K, V, R> biFunction) {
+		if (null == map || null == biFunction) {
+			return MapUtil.newHashMap();
+		}
+		return map.entrySet().stream().collect(Collectors.toMap(Map.Entry::getKey, m -> biFunction.apply(m.getKey(), m.getValue())));
+	}
+
 	/**
 	 * 过滤Map保留指定键值对，如果键不存在跳过
 	 *

hutool-core/src/test/java/cn/hutool/core/map/MapUtilTest.java

@@ -1,15 +1,44 @@
 package cn.hutool.core.map;
 
 import cn.hutool.core.convert.Convert;
+import cn.hutool.core.lang.Opt;
 import cn.hutool.core.util.StrUtil;
+import lombok.Builder;
+import lombok.Data;
 import org.junit.Assert;
 import org.junit.Test;
 
-import java.util.HashMap;
-import java.util.Map;
+import java.util.*;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 public class MapUtilTest {
 
+	enum PeopleEnum {GIRL, BOY, CHILD}
+
+	@Data
+	@Builder
+	public static class User {
+		private Long id;
+		private String name;
+	}
+
+	@Data
+	@Builder
+	public static class Group {
+		private Long id;
+		private List<User> users;
+	}
+
+	@Data
+	@Builder
+	public static class UserGroup {
+		private Long userId;
+		private Long groupId;
+	}
+
+
 	@Test
 	public void filterTest() {
 		Map<String, String> map = MapUtil.newHashMap();
@@ -26,6 +55,47 @@ public class MapUtilTest {
 		Assert.assertEquals("4", map2.get("d"));
 	}
 
+	@Test
+	public void changeTest() {
+		// Add test like a foreigner
+		Map<Integer, String> adjectivesMap = MapUtil.<Integer, String>builder()
+				.put(0, "lovely")
+				.put(1, "friendly")
+				.put(2, "happily")
+				.build();
+
+		Map<Integer, String> resultMap = MapUtil.change(adjectivesMap, (k, v) -> v + " " + PeopleEnum.values()[k].name().toLowerCase());
+
+		Assert.assertEquals("lovely girl", resultMap.get(0));
+		Assert.assertEquals("friendly boy", resultMap.get(1));
+		Assert.assertEquals("happily child", resultMap.get(2));
+
+		// 下单用户，Queue表示正在 .排队. 抢我抢不到的二次元周边！
+		Queue<String> customers = new ArrayDeque<>(Arrays.asList("刑部尚书手工耿", "木瓜大盗大漠叔", "竹鼠发烧找华农", "朴实无华朱一旦"));
+		// 分组
+		List<Group> groups = Stream.iterate(0L, i -> ++i).limit(4).map(i -> Group.builder().id(i).build()).collect(Collectors.toList());
+		// 如你所见，它是一个map，key由用户id，value由用户组成
+		Map<Long, User> idUserMap = Stream.iterate(0L, i -> ++i).limit(4).map(i -> User.builder().id(i).name(customers.poll()).build()).collect(Collectors.toMap(User::getId, Function.identity()));
+		// 如你所见，它是一个map，key由分组id，value由用户ids组成，典型的多对多关系
+		Map<Long, List<Long>> groupIdUserIdsMap = groups.stream().flatMap(group -> idUserMap.keySet().stream().map(userId -> UserGroup.builder().groupId(group.getId()).userId(userId).build())).collect(Collectors.groupingBy(UserGroup::getUserId, Collectors.mapping(UserGroup::getGroupId, Collectors.toList())));
+
+		// 神奇的魔法发生了， 分组id和用户ids组成的map，竟然变成了订单编号和用户实体集合组成的map
+		Map<Long, List<User>> groupIdUserMap = MapUtil.change(groupIdUserIdsMap, (groupId, userIds) -> userIds.stream().map(idUserMap::get).collect(Collectors.toList()));
+
+		// 然后你就可以拿着这个map，去封装groups，使其能够在订单数据带出客户信息啦
+		groups.forEach(group -> Opt.ofNullable(group.getId()).map(groupIdUserMap::get).ifPresent(group::setUsers));
+
+		// 下面是测试报告
+		groups.forEach(group -> {
+			List<User> users = group.getUsers();
+			Assert.assertEquals("刑部尚书手工耿", users.get(0).getName());
+			Assert.assertEquals("木瓜大盗大漠叔", users.get(1).getName());
+			Assert.assertEquals("竹鼠发烧找华农", users.get(2).getName());
+			Assert.assertEquals("朴实无华朱一旦", users.get(3).getName());
+		});
+		// 能写代码真开心
+	}
+
 	@Test
 	public void filterMapWrapperTest() {
 		Map<String, String> map = MapUtil.newHashMap();