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Table of Contents

Status

Current state: Accepted

Under Discussion thread: here

Discussion Vote thread: here

JIRA: here

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

...

ConsumerGroupMetadata class should be an sealed interface, we should provide a new internal permitted class for interface implementation and use java default scope for class visibility.

Code Block
languagejava
titleConsumerGroupMetadata
public interface ConsumerGroupMetadata {

    String groupId();

    int generationIdmemberEpoch();

    String memberId();

    Optional<String> groupInstanceId();
}

...

Code Block
languagejava
titleDefaultConsumerGroupMetadata
class DefaultConsumerGroupMetadata implements ConsumerGroupMetadata {
    private final String groupId;
    private final int generationIdmemberEpoch;
    private final String memberId;
    private final Optional<String> groupInstanceId;

    DefaultConsumerGroupMetadata(String groupId,
                                        int generationIdmemberEpoch,
                                        String memberId,
                                        Optional<String> groupInstanceId) {
        this.groupId = Objects.requireNonNull(groupId, "group.id can't be null");
        this.generationId memberEpoch= generationIdmemberEpoch;
        this.memberId = Objects.requireNonNull(memberId, "member.id can't be null");
        this.groupInstanceId = Objects.requireNonNull(groupInstanceId, "group.instance.id can't be null");
    }

    public String groupId() {
        return groupId;
    }

    public int generationIdmemberEpoch() {
        return generationIdmemberEpoch;
    }

    public String memberId() {
        return memberId;
    }

    public Optional<String> groupInstanceId() {
        return groupInstanceId;
    }

    @Override
    public String toString() {
        return String.format("GroupMetadata(groupId = %s, generationId memberEpoch= %d, memberId = %s, groupInstanceId = %s)",
                groupId,
                generationIdmemberEpoch,
                memberId,
                groupInstanceId.orElse(""));
    }

    @Override
    public boolean equals(final Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        final DefaultConsumerGroupMetadata that = (DefaultConsumerGroupMetadata) o;
        return generationId memberEpoch== that.generationIdmemberEpoch &&
                Objects.equals(groupId, that.groupId) &&
                Objects.equals(memberId, that.memberId) &&
                Objects.equals(groupInstanceId, that.groupInstanceId);
    }

    @Override
    public int hashCode() {
        return Objects.hash(groupId, generationIdmemberEpoch, memberId, groupInstanceId);
    }

}

Compatibility, Deprecation, and Migration Plan

  • Change is impacting all users using any available constructor of ConsumerGroupMetadata class.
  • For Kafka 4.12.0, we should keep the the ConsumerGroupMetadata class as-is for backward compatibility, but deprecate all constructors and update the JavaDocs to indicate this class will become an interface in the future.
  • For Kafka 5.0, we do the actual code change from class to interface.
  • Once Kafka clients stop supporting Java 11 we can mark the ConsumerGroupMetadata interface as sealed with only default implementation permitted.

Test Plan

Automated tests which are part of CI will cover necessary tests.

...

Code Block
languagejava
titlealternative
publicclass DefaultConsumerGroupMetadata classimplements ConsumerGroupMetadata {
    private final String groupId;
    private final int generationIdmemberEpoch;
    private final String memberId;
    private final Optional<String> groupInstanceId;

    public ConsumerGroupMetadata newInstance(KafkaConsumer<?,?> kafkaConsumer) {
        return kafkaConsumer.groupMetadata();
    }
    
    private ConsumerGroupMetadataDefaultConsumerGroupMetadata(String groupId,
                                 int generationIdmemberEpoch,
                                 String memberId,
                                 Optional<String> groupInstanceId) {
        this.groupId = Objects.requireNonNull(groupId, "group.id can't be null");
        this.generationId memberEpoch= generationIdmemberEpoch;
        this.memberId = Objects.requireNonNull(memberId, "member.id can't be null");
        this.groupInstanceId = Objects.requireNonNull(groupInstanceId, "group.instance.id can't be null");
    }

    private ConsumerGroupMetadata(String groupId) {
        this(groupId,
            JoinGroupRequest.UNKNOWN_GENERATION_ID,
            JoinGroupRequest.UNKNOWN_MEMBER_ID,
            Optional.empty());
    }

    public String groupId() {
        return groupId;
    }

    public int generationIdmemberEpoch() {
        return generationIdmemberEpoch;
    }

    public String memberId() {
        return memberId;
    }

    public Optional<String> groupInstanceId() {
        return groupInstanceId;
    }

    @Override
    public String toString() {
        return String.format("GroupMetadata(groupId = %s, generationId memberEpoch= %d, memberId = %s, groupInstanceId = %s)",
                groupId,
               generationId memberEpoch,
                memberId,
                groupInstanceId.orElse(""));
    }

    @Override
    public boolean equals(final Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        final ConsumerGroupMetadataDefaultConsumerGroupMetadata that = (ConsumerGroupMetadataDefaultConsumerGroupMetadata) o;
        return generationId memberEpoch== that.generationIdmemberEpoch &&
                Objects.equals(groupId, that.groupId) &&
                Objects.equals(memberId, that.memberId) &&
                Objects.equals(groupInstanceId, that.groupInstanceId);
    }

    @Override
    public int hashCode() {
        return Objects.hash(groupId, generationIdmemberEpoch, memberId, groupInstanceId);
    }

}