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添加支持对值集合进行映射的分组方法

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huangchengxing 2022-10-19 11:21:31 +08:00
parent c56f36ac4f
commit d799e43e54
2 changed files with 85 additions and 0 deletions
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61
hutool-core/src/main/java/cn/hutool/core/stream/CollectorUtil.java
View File

@ -147,6 +147,67 @@ public class CollectorUtil {
return groupingBy(classifier, Collectors.toList());
}
/**
* 提供对null值友好的groupingBy操作的{@link Collector}实现，
* 对集合分组，然后对分组后的值集合进行映射
*
* @param classifier 分组依据
* @param valueMapper 值映射方法
* @param valueCollFactory 值集合的工厂方法
* @param mapFactory Map集合的工厂方法
* @param <T> 元素类型
* @param <K> 键类型
* @param <R> 值类型
* @param <C> 值集合类型
* @param <M> 返回的Map集合类型
* @return {@link Collector}
*/
public static <T, K, R, C extends Collection<R>, M extends Map<K, C>> Collector<T, ?, M> groupingBy(
final Function<? super T, ? extends K> classifier,
final Function<? super T, ? extends R> valueMapper,
final Supplier<C> valueCollFactory,
final Supplier<M> mapFactory) {
return groupingBy(classifier, mapFactory, Collectors.mapping(
valueMapper, Collectors.toCollection(valueCollFactory)
));
}
/**
* 提供对null值友好的groupingBy操作的{@link Collector}实现，
* 对集合分组，然后对分组后的值集合进行映射
*
* @param classifier 分组依据
* @param valueMapper 值映射方法
* @param valueCollFactory 值集合的工厂方法
* @param <T> 元素类型
* @param <K> 键类型
* @param <R> 值类型
* @param <C> 值集合类型
* @return {@link Collector}
*/
public static <T, K, R, C extends Collection<R>> Collector<T, ?, Map<K, C>> groupingBy(
final Function<? super T, ? extends K> classifier,
final Function<? super T, ? extends R> valueMapper,
final Supplier<C> valueCollFactory) {
return groupingBy(classifier, valueMapper, valueCollFactory, HashMap::new);
}
/**
* 提供对null值友好的groupingBy操作的{@link Collector}实现，
* 对集合分组，然后对分组后的值集合进行映射
*
* @param classifier 分组依据
* @param valueMapper 值映射方法
* @param <T> 元素类型
* @param <K> 键类型
* @param <R> 值类型
* @return {@link Collector}
*/
public static <T, K, R> Collector<T, ?, Map<K, List<R>>> groupingBy(
final Function<? super T, ? extends K> classifier,
final Function<? super T, ? extends R> valueMapper) {
return groupingBy(classifier, valueMapper, ArrayList::new, HashMap::new);
}
/**
* 对null友好的 toMap 操作的 {@link Collector}实现，默认使用HashMap

24
hutool-core/src/test/java/cn/hutool/core/stream/CollectorUtilTest.java
View File

@ -78,4 +78,28 @@ public class CollectorUtilTest {
.put(3, 1L)
.build(), map);
}
@Test
public void testGroupingByAfterValueMapped() {
List<Integer> list = Arrays.asList(1, 1, 2, 2, 3, 4);
Map<Boolean, Set<String>> map = list.stream()
.collect(CollectorUtil.groupingBy(t -> (t & 1) == 0, String::valueOf, LinkedHashSet::new, LinkedHashMap::new));
Assert.assertEquals(LinkedHashMap.class, map.getClass());
Assert.assertEquals(new LinkedHashSet<>(Arrays.asList("2", "4")), map.get(Boolean.TRUE));
Assert.assertEquals(new LinkedHashSet<>(Arrays.asList("1", "3")), map.get(Boolean.FALSE));
map = list.stream()
.collect(CollectorUtil.groupingBy(t -> (t & 1) == 0, String::valueOf, LinkedHashSet::new));
Assert.assertEquals(HashMap.class, map.getClass());
Assert.assertEquals(new LinkedHashSet<>(Arrays.asList("2", "4")), map.get(Boolean.TRUE));
Assert.assertEquals(new LinkedHashSet<>(Arrays.asList("1", "3")), map.get(Boolean.FALSE));
Map<Boolean, List<String>> map2 = list.stream()
.collect(CollectorUtil.groupingBy(t -> (t & 1) == 0, String::valueOf));
Assert.assertEquals(Arrays.asList("2", "2", "4"), map2.get(Boolean.TRUE));
Assert.assertEquals(Arrays.asList("1", "1", "3"), map2.get(Boolean.FALSE));
}
}