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KAFKA-20297: Cleanup org.apache.kafka.common.utils.CollectionUtils #21818

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KAFKA-20297: Cleanup org.apache.kafka.common.utils.CollectionUtils #21818

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98a9db1
KAFKA-20297: Remove groupPartitionsByTopic/groupPartitionDataByTopic …
unknowntpo Mar 21, 2026
5c081f1
KAFKA-20297: Inline subtractMap and delete CollectionUtils
unknowntpo Mar 21, 2026
4aea5f0
KAFKA-20297: Simplify StickyAssignor partition grouping with helper m…
unknowntpo Mar 21, 2026
05ad35d
KAFKA-20297: Extract groupPartitionDataByTopic helper in DescribeProd…
unknowntpo Mar 21, 2026
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17 changes: 9 additions & 8 deletions clients/src/main/java/org/apache/kafka/clients/admin/internals/DescribeProducersHandler.java
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Expand Up @@ -30,7 +30,6 @@
import org.apache.kafka.common.requests.ApiError;
import org.apache.kafka.common.requests.DescribeProducersRequest;
import org.apache.kafka.common.requests.DescribeProducersResponse;
import org.apache.kafka.common.utils.CollectionUtils;
import org.apache.kafka.common.utils.LogContext;

import org.slf4j.Logger;
Expand Down Expand Up @@ -89,15 +88,17 @@ public DescribeProducersRequest.Builder buildBatchedRequest(
Set<TopicPartition> topicPartitions
) {
DescribeProducersRequestData request = new DescribeProducersRequestData();
DescribeProducersRequest.Builder builder = new DescribeProducersRequest.Builder(request);

CollectionUtils.groupPartitionsByTopic(
topicPartitions,
builder::addTopic,
(topicRequest, partitionId) -> topicRequest.partitionIndexes().add(partitionId)
);
for (TopicPartition tp : topicPartitions) {
DescribeProducersRequestData.TopicRequest topicRequest = request.topics().find(tp.topic());
if (topicRequest == null) {
topicRequest = new DescribeProducersRequestData.TopicRequest().setName(tp.topic());
request.topics().add(topicRequest);
}
topicRequest.partitionIndexes().add(tp.partition());
}

return builder;
return new DescribeProducersRequest.Builder(request);
}

private void handlePartitionError(
Expand Down
21 changes: 9 additions & 12 deletions clients/src/main/java/org/apache/kafka/clients/admin/internals/ListOffsetsHandler.java
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Expand Up @@ -32,7 +32,6 @@
import org.apache.kafka.common.requests.AbstractResponse;
import org.apache.kafka.common.requests.ListOffsetsRequest;
import org.apache.kafka.common.requests.ListOffsetsResponse;
import org.apache.kafka.common.utils.CollectionUtils;
import org.apache.kafka.common.utils.LogContext;

import org.slf4j.Logger;
Expand Down Expand Up @@ -80,17 +79,15 @@ public AdminApiLookupStrategy<TopicPartition> lookupStrategy() {

@Override
ListOffsetsRequest.Builder buildBatchedRequest(int brokerId, Set<TopicPartition> keys) {
Map<String, ListOffsetsTopic> topicsByName = CollectionUtils.groupPartitionsByTopic(
keys,
topicName -> new ListOffsetsTopic().setName(topicName),
(listOffsetsTopic, partitionId) -> {
TopicPartition topicPartition = new TopicPartition(listOffsetsTopic.name(), partitionId);
long offsetTimestamp = offsetTimestampsByPartition.get(topicPartition);
listOffsetsTopic.partitions().add(
new ListOffsetsPartition()
.setPartitionIndex(partitionId)
.setTimestamp(offsetTimestamp));
});
Map<String, ListOffsetsTopic> topicsByName = new HashMap<>();
for (TopicPartition topicPartition : keys) {
ListOffsetsTopic topic = topicsByName.computeIfAbsent(
topicPartition.topic(), t -> new ListOffsetsTopic().setName(t));
long offsetTimestamp = offsetTimestampsByPartition.get(topicPartition);
topic.partitions().add(new ListOffsetsPartition()
.setPartitionIndex(topicPartition.partition())
.setTimestamp(offsetTimestamp));
}
boolean supportsMaxTimestamp = keys
.stream()
.anyMatch(key -> offsetTimestampsByPartition.get(key) == ListOffsetsRequest.MAX_TIMESTAMP);
Expand Down
11 changes: 9 additions & 2 deletions clients/src/main/java/org/apache/kafka/clients/consumer/StickyAssignor.java
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Expand Up @@ -23,15 +23,16 @@
import org.apache.kafka.common.protocol.types.Schema;
import org.apache.kafka.common.protocol.types.Struct;
import org.apache.kafka.common.protocol.types.Type;
import org.apache.kafka.common.utils.CollectionUtils;

import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Collectors;

/**
* <p>The sticky assignor serves two purposes. First, it guarantees an assignment that is as balanced as possible, meaning either:
Expand Down Expand Up @@ -230,7 +231,8 @@ protected MemberData memberData(Subscription subscription) {
static ByteBuffer serializeTopicPartitionAssignment(MemberData memberData) {
Struct struct = new Struct(STICKY_ASSIGNOR_USER_DATA_V1);
List<Struct> topicAssignments = new ArrayList<>();
for (Map.Entry<String, List<Integer>> topicEntry : CollectionUtils.groupPartitionsByTopic(memberData.partitions).entrySet()) {
Map<String, List<Integer>> partitionsByTopic = groupPartitionsByTopic(memberData.partitions);
for (Map.Entry<String, List<Integer>> topicEntry : partitionsByTopic.entrySet()) {
Struct topicAssignment = new Struct(TOPIC_ASSIGNMENT);
topicAssignment.set(TOPIC_KEY_NAME, topicEntry.getKey());
topicAssignment.set(PARTITIONS_KEY_NAME, topicEntry.getValue().toArray());
Expand Down Expand Up @@ -272,4 +274,9 @@ private static MemberData deserializeTopicPartitionAssignment(ByteBuffer buffer)
Optional<Integer> generation = struct.hasField(GENERATION_KEY_NAME) ? Optional.of(struct.getInt(GENERATION_KEY_NAME)) : Optional.empty();
return new MemberData(partitions, generation);
}

private static Map<String, List<Integer>> groupPartitionsByTopic(Collection<TopicPartition> partitions) {
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@chia7712 chia7712 Mar 21, 2026

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Could you inline it?

return partitions.stream()
.collect(Collectors.groupingBy(TopicPartition::topic, Collectors.mapping(TopicPartition::partition, Collectors.toList())));
}
}
9 changes: 7 additions & 2 deletions .../org/apache/kafka/common/security/oauthbearer/OAuthBearerExtensionsValidatorCallback.java
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Expand Up @@ -22,11 +22,10 @@
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.stream.Collectors;

import javax.security.auth.callback.Callback;

import static org.apache.kafka.common.utils.CollectionUtils.subtractMap;

/**
* A {@code Callback} for use by the {@code SaslServer} implementation when it
* needs to validate the SASL extensions for the OAUTHBEARER mechanism
Expand Down Expand Up @@ -90,6 +89,12 @@ public Map<String, String> ignoredExtensions() {
return Collections.unmodifiableMap(subtractMap(subtractMap(inputExtensions.map(), invalidExtensions), validatedExtensions));
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@chia7712 chia7712 Mar 21, 2026

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The original logic will create map repeatedly. Could you use for-loop to streamline it?

public Map<String, String> ignoredExtensions() {
    Map<String, String> ignored = new HashMap<>();
    for (Map.Entry<String, String> entry : inputExtensions.map().entrySet()) {
        String key = entry.getKey();
        if (!invalidExtensions.containsKey(key) && !validatedExtensions.containsKey(key)) {
            ignored.put(key, entry.getValue());
        }
    }
    return Collections.unmodifiableMap(ignored);
}

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@unknowntpo unknowntpo Mar 22, 2026

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I thought the subtractMap is more Functional Programming style, more declarative, and this path is unlikely a hot path, which is not suitable for repeating memory allocation, but your approach is okay for me, I'll change it.

}

private static Map<String, String> subtractMap(Map<String, String> minuend, Map<String, String> subtrahend) {
return minuend.entrySet().stream()
.filter(entry -> !subtrahend.containsKey(entry.getKey()))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
}

/**
* Validates a specific extension in the original {@code inputExtensions} map
* @param extensionName - the name of the extension which was validated
Expand Down
93 changes: 0 additions & 93 deletions clients/src/main/java/org/apache/kafka/common/utils/CollectionUtils.java
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This file was deleted.

2 changes: 1 addition & 1 deletion clients/src/main/resources/common/message/DescribeProducersRequest.json
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Expand Up @@ -23,7 +23,7 @@
"fields": [
{ "name": "Topics", "type": "[]TopicRequest", "versions": "0+",
"about": "The topics to list producers for.", "fields": [
{ "name": "Name", "type": "string", "versions": "0+", "entityType": "topicName",
{ "name": "Name", "type": "string", "versions": "0+", "mapKey": true, "entityType": "topicName",
"about": "The topic name." },
{ "name": "PartitionIndexes", "type": "[]int32", "versions": "0+",
"about": "The indexes of the partitions to list producers for." }
Expand Down
13 changes: 10 additions & 3 deletions .../src/test/java/org/apache/kafka/clients/admin/internals/DescribeProducersHandlerTest.java
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Expand Up @@ -33,7 +33,6 @@
import org.apache.kafka.common.protocol.Errors;
import org.apache.kafka.common.requests.DescribeProducersRequest;
import org.apache.kafka.common.requests.DescribeProducersResponse;
import org.apache.kafka.common.utils.CollectionUtils;
import org.apache.kafka.common.utils.LogContext;

import org.junit.jupiter.api.Test;
Expand Down Expand Up @@ -120,7 +119,7 @@ public void testBuildRequest() {
int brokerId = 3;
DescribeProducersRequest.Builder request = handler.buildBatchedRequest(brokerId, topicPartitions);

List<DescribeProducersRequestData.TopicRequest> topics = request.data.topics();
DescribeProducersRequestData.TopicRequestCollection topics = request.data.topics();

assertEquals(Set.of("foo", "bar"), topics.stream()
.map(DescribeProducersRequestData.TopicRequest::name)
Expand Down Expand Up @@ -308,7 +307,7 @@ private DescribeProducersResponse describeProducersResponse(
) {
DescribeProducersResponseData response = new DescribeProducersResponseData();
Map<String, Map<Integer, PartitionResponse>> partitionResponsesByTopic =
CollectionUtils.groupPartitionDataByTopic(partitionResponses);
groupPartitionDataByTopic(partitionResponses);

for (Map.Entry<String, Map<Integer, PartitionResponse>> topicEntry : partitionResponsesByTopic.entrySet()) {
String topic = topicEntry.getKey();
Expand All @@ -327,4 +326,12 @@ private DescribeProducersResponse describeProducersResponse(
return new DescribeProducersResponse(response);
}

private static Map<String, Map<Integer, PartitionResponse>> groupPartitionDataByTopic(
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we don't use such complex structure in tests actually. Maybe we could use describeProducersResponse(TopicPartition partition, PartitionResponse partitionResponse) instead

Map<TopicPartition, PartitionResponse> partitionResponses
) {
return partitionResponses.entrySet().stream()
.collect(Collectors.groupingBy(
e -> e.getKey().topic(),
Collectors.toMap(e -> e.getKey().partition(), Map.Entry::getValue)));
}
}
7 changes: 5 additions & 2 deletions clients/src/test/java/org/apache/kafka/clients/consumer/StickyAssignorTest.java
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Expand Up @@ -25,7 +25,6 @@
import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.protocol.types.Struct;
import org.apache.kafka.common.test.api.Flaky;
import org.apache.kafka.common.utils.CollectionUtils;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.Timeout;
Expand Down Expand Up @@ -368,7 +367,11 @@ public void testAssignorWithOldVersionSubscriptions() {
private Subscription buildSubscriptionWithOldSchema(List<String> topics, List<TopicPartition> partitions, int consumerIndex) {
Struct struct = new Struct(StickyAssignor.STICKY_ASSIGNOR_USER_DATA_V0);
List<Struct> topicAssignments = new ArrayList<>();
for (Map.Entry<String, List<Integer>> topicEntry : CollectionUtils.groupPartitionsByTopic(partitions).entrySet()) {
Map<String, List<Integer>> partitionsByTopic = new HashMap<>();
for (TopicPartition tp : partitions) {
partitionsByTopic.computeIfAbsent(tp.topic(), t -> new ArrayList<>()).add(tp.partition());
}
for (Map.Entry<String, List<Integer>> topicEntry : partitionsByTopic.entrySet()) {
Struct topicAssignment = new Struct(StickyAssignor.TOPIC_ASSIGNMENT);
topicAssignment.set(StickyAssignor.TOPIC_KEY_NAME, topicEntry.getKey());
topicAssignment.set(StickyAssignor.PARTITIONS_KEY_NAME, topicEntry.getValue().toArray());
Expand Down
11 changes: 8 additions & 3 deletions ...src/test/java/org/apache/kafka/clients/consumer/internals/AbstractStickyAssignorTest.java
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Expand Up @@ -23,7 +23,6 @@
import org.apache.kafka.common.PartitionInfo;
import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.test.api.Flaky;
import org.apache.kafka.common.utils.CollectionUtils;
import org.apache.kafka.common.utils.Utils;

import org.junit.jupiter.api.BeforeEach;
Expand All @@ -36,6 +35,7 @@
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
Expand Down Expand Up @@ -1428,6 +1428,11 @@ private String pad(int num, int digits) {
return "0".repeat(Math.max(0, digits - iDigits)) + num;
}

private static Map<String, List<Integer>> groupPartitionsByTopic(Collection<TopicPartition> partitions) {
return partitions.stream()
.collect(Collectors.groupingBy(TopicPartition::topic, Collectors.mapping(TopicPartition::partition, Collectors.toList())));
}

protected static List<String> topics(String... topics) {
return Arrays.asList(topics);
}
Expand Down Expand Up @@ -1522,8 +1527,8 @@ protected void verifyValidityAndBalance(Map<String, Subscription> subscriptions,
if (Math.abs(len - otherLen) <= 1)
continue;

Map<String, List<Integer>> map = CollectionUtils.groupPartitionsByTopic(partitions);
Map<String, List<Integer>> otherMap = CollectionUtils.groupPartitionsByTopic(otherPartitions);
Map<String, List<Integer>> map = groupPartitionsByTopic(partitions);
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we could streamline the test.

Set<String> otherTopics = otherPartitions.stream()
    .map(TopicPartition::topic)
    .collect(Collectors.toSet());

for (TopicPartition tp : partitions) {
    assertFalse(otherTopics.contains(tp.topic()), 
        "Error: Some partitions can be moved...");
}

Map<String, List<Integer>> otherMap = groupPartitionsByTopic(otherPartitions);

int moreLoaded = len > otherLen ? i : j;
int lessLoaded = len > otherLen ? j : i;
Expand Down
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