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Improve type safety of CollectionUtils.toTreeSet #16306

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Improve type safety of CollectionUtils.toTreeSet #16306

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a5a64f9
Improve type safety of CollectionUtils.toTreeSet
skt-shinyruo Jun 2, 2026
630215f
Add null coverage for toTreeSet comparator overload
skt-shinyruo Jun 3, 2026
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11 changes: 10 additions & 1 deletion dubbo-common/src/main/java/org/apache/dubbo/common/utils/CollectionUtils.java
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Original file line number Diff line number Diff line change
Expand Up @@ -419,7 +419,7 @@ public static <T> T first(List<T> values) {
return values.get(0);
}

public static <T> Set<T> toTreeSet(Set<T> set) {
public static <T extends Comparable<? super T>> Set<T> toTreeSet(Set<T> set) {
if (isEmpty(set)) {
return set;
}
Expand All @@ -429,6 +429,15 @@ public static <T> Set<T> toTreeSet(Set<T> set) {
return set;
}

public static <T> Set<T> toTreeSet(Set<T> set, Comparator<? super T> comparator) {
if (set == null) {
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@RainYuY RainYuY Jun 3, 2026

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Why did it become null instead of checking for empty?

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@skt-shinyruo skt-shinyruo Jun 3, 2026

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The null check is intentional here. For this comparator overload, null and empty inputs need different handling: null keeps the existing null-return behavior, while an empty non-null set should still return an empty TreeSet initialized with the provided comparator. Returning the original set from isEmpty(set) would lose that comparator. The addAll call is a no-op for an empty set.

I also added a null-input test for this overload in 630215f.

return set;
}
Set<T> treeSet = new TreeSet<>(comparator);
treeSet.addAll(set);
return treeSet;
}

public static <T> Set<T> newHashSet(int expectedSize) {
return new HashSet<>(capacity(expectedSize));
}
Expand Down
43 changes: 43 additions & 0 deletions dubbo-common/src/test/java/org/apache/dubbo/common/utils/CollectionUtilsTest.java
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Expand Up @@ -21,12 +21,14 @@
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
Expand Down Expand Up @@ -255,6 +257,34 @@ void sortShouldSupportComparableSuperType() {
assertEquals("b", sorted.get(1).getName());
}

@Test
void toTreeSetShouldSupportExplicitComparator() {
Set<PriorityItem> items = new LinkedHashSet<>(Arrays.asList(new PriorityItem(3), new PriorityItem(1)));

Set<PriorityItem> sorted = CollectionUtils.toTreeSet(items, Comparator.comparingInt(PriorityItem::getPriority));

List<PriorityItem> sortedList = new ArrayList<>(sorted);
assertEquals(1, sortedList.get(0).getPriority());
assertEquals(3, sortedList.get(1).getPriority());
}

@Test
void toTreeSetShouldPreserveComparatorForEmptyInput() {
Comparator<PriorityItem> comparator = Comparator.comparingInt(PriorityItem::getPriority);

Set<PriorityItem> sorted = CollectionUtils.toTreeSet(new LinkedHashSet<>(), comparator);

assertTrue(sorted instanceof TreeSet);
Assertions.assertSame(comparator, ((TreeSet<PriorityItem>) sorted).comparator());
}

@Test
void toTreeSetShouldReturnNullForNullInputWithComparator() {
Comparator<PriorityItem> comparator = Comparator.comparingInt(PriorityItem::getPriority);

assertNull(CollectionUtils.toTreeSet(null, comparator));
}

private static class Person implements Comparable<Person> {

private final String name;
Expand All @@ -279,4 +309,17 @@ private Student(String name) {
super(name);
}
}

private static class PriorityItem {

private final int priority;

private PriorityItem(int priority) {
this.priority = priority;
}

private int getPriority() {
return priority;
}
}
}
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