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!676 【6.x】新增CollectorUtil.reduceListMap()用于Collection<Map<K,V>> => Map<K,List<V>>,优化groupingBy中对null的处理
Merge pull request !676 from 阿超/v6-dev
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commit
6f97c9ed42
@ -2,6 +2,7 @@ package cn.hutool.core.stream;
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import cn.hutool.core.lang.Opt;
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import cn.hutool.core.text.StrUtil;
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import cn.hutool.core.util.ArrayUtil;
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import java.util.Collections;
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import java.util.EnumSet;
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@ -9,6 +10,8 @@ import java.util.HashMap;
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import java.util.Map;
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import java.util.Set;
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import java.util.List;
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import java.util.ArrayList;
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import java.util.Objects;
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import java.util.StringJoiner;
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import java.util.function.BiConsumer;
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import java.util.function.BinaryOperator;
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@ -104,7 +107,10 @@ public class CollectorUtil {
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final BiConsumer<Map<K, A>, T> accumulator = (m, t) -> {
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final K key = Opt.ofNullable(t).map(classifier).orElse(null);
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final A container = m.computeIfAbsent(key, k -> downstreamSupplier.get());
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downstreamAccumulator.accept(container, t);
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if (ArrayUtil.isArray(container) || Objects.nonNull(t)) {
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// 如果是数组类型,不需要判空,场景——分组后需要使用:java.util.stream.Collectors.counting 求null元素个数
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downstreamAccumulator.accept(container, t);
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}
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};
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final BinaryOperator<Map<K, A>> merger = mapMerger(downstream.combiner());
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@SuppressWarnings("unchecked") final Supplier<Map<K, A>> mangledFactory = (Supplier<Map<K, A>>) mapFactory;
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@ -211,5 +217,39 @@ public class CollectorUtil {
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};
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}
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/**
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* 聚合这种数据类型:{@code Collection<Map<K,V>> => Map<K,List<V>>}
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* 其中key相同的value,会累加到List中
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*
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* @param <K> key的类型
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* @param <V> value的类型
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* @return 聚合后的map
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*/
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public static <K, V> Collector<Map<K, V>, ?, Map<K, List<V>>> reduceListMap() {
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return reduceListMap(HashMap::new);
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}
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/**
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* 聚合这种数据类型:{@code Collection<Map<K,V>> => Map<K,List<V>>}
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* 其中key相同的value,会累加到List中
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*
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* @param mapSupplier 可自定义map的类型如concurrentHashMap等
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* @param <K> key的类型
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* @param <V> value的类型
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* @param <R> 返回值的类型
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* @return 聚合后的map
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*/
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public static <K, V, R extends Map<K, List<V>>> Collector<Map<K, V>, ?, R> reduceListMap(final Supplier<R> mapSupplier) {
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return Collectors.reducing(mapSupplier.get(), value -> {
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R result = mapSupplier.get();
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value.forEach((k, v) -> result.computeIfAbsent(k, i -> new ArrayList<>()).add(v));
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return result;
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}, (l, r) -> {
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r.forEach((k, v) -> l.computeIfAbsent(k, i -> new ArrayList<>()).addAll(v));
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return l;
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}
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);
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}
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}
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@ -153,7 +153,7 @@ public class CollStreamUtilTest {
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// 对null友好
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final Map<Long, Map<Long, Student>> termIdClassIdStudentMap = CollStreamUtil.group2Map(Arrays.asList(null, new Student(2, 2, 1, "王五")), Student::getTermId, Student::getClassId);
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final Map<Long, Map<Long, Student>> termIdClassIdStudentCompareMap = new HashMap<Long, Map<Long, Student>>() {{
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put(null, MapUtil.of(null, null));
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put(null, MapUtil.empty());
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put(2L, MapUtil.of(2L, new Student(2, 2, 1, "王五")));
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}};
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Assert.assertEquals(termIdClassIdStudentCompareMap, termIdClassIdStudentMap);
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@ -215,7 +215,7 @@ public class CollStreamUtilTest {
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new Student(1, 2, 1, "李四"));
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final Map<Long, List<Student>> termIdStudentsMap = CollStreamUtil.groupBy(students, Student::getTermId, Collectors.toList());
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final Map<Long, List<Student>> termIdStudentsCompareMap = new HashMap<>();
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termIdStudentsCompareMap.put(null, Arrays.asList(null, null));
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termIdStudentsCompareMap.put(null, Collections.emptyList());
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termIdStudentsCompareMap.put(1L, Arrays.asList(new Student(1L, 1, 1, "张三"), new Student(1L, 2, 1, "李四")));
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Assert.assertEquals(termIdStudentsCompareMap, termIdStudentsMap);
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@ -0,0 +1,37 @@
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package cn.hutool.core.stream;
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import cn.hutool.core.map.MapUtil;
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import org.junit.Assert;
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import org.junit.Test;
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import java.util.Arrays;
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import java.util.List;
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import java.util.Map;
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import java.util.Set;
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import java.util.stream.Collectors;
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/**
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* CollectorUtilTest
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*
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* @author VampireAchao
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* @since 2022/7/3
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*/
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public class CollectorUtilTest {
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@Test
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public void reduceListMapTest() {
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Set<Map<String, Integer>> nameScoreMapList = StreamUtil.of(
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// 集合内的第一个map,包含两个key value
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MapUtil.builder("苏格拉底", 1).put("特拉叙马霍斯", 3).build(),
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MapUtil.of("苏格拉底", 2),
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MapUtil.of("特拉叙马霍斯", 1),
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MapUtil.of("特拉叙马霍斯", 2)
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).collect(Collectors.toSet());
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// 执行聚合
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Map<String, List<Integer>> nameScoresMap = nameScoreMapList.stream().collect(CollectorUtil.reduceListMap());
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Assert.assertEquals(MapUtil.builder("苏格拉底", Arrays.asList(1, 2))
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.put("特拉叙马霍斯", Arrays.asList(3, 1, 2)).build(),
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nameScoresMap);
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}
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}
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