Status

Current state: Under DiscussionAccepted (2.2.0)

Discussion thread: Link here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: KAFKA-7402

Motivation

...

"Various components in Streams have close methods but do not implement AutoCloseable. This means that they can't be used in try-with-resources blocks.

...

KafkaStreams itself is a notable example of this, but we can take the opportunity to look for other components that make sense as AutoCloseable as well."

So these classes can be used in a try-with-resources Statement after implementing AutoCloseable.

From AutoCloseable's Javadoc:

An object that may hold resources (such as file or socket handles) until it is closed. The {@link #close()} method of an {@code AutoCloseable} object is called automatically when exiting a {@code try}-with-resources block for which the object has been declared in the resource specification header. This construction ensures prompt release, avoiding resource exhaustion exceptions and errors that may otherwise occur.

Public Interfaces

By going over the project, here is a list that I found which can implement AutoCloseable. Suggestions are welcome.

1. org.apache.kafka.streams.KafkaStreams
2. org.apache.kafka.streams.processor.internals.RecordCollectorImplRecordCollector
3. org.apache.kafka.connect.runtime.ConnectMetrics.MetricGroup
4. org.apache.kafka.connect.transforms.TimestampRouter
5. org.apache.kafka.tools.VerifiableProducer

Additions provided by Chia-pingChia-Ping Tsai:

1. org.apache.kafka.connect.runtime.WorkerConnector.ConnectorMetricsGroup
2. org.apache.kafka.common.record.MemoryRecordsBuilder
3. org.apache.kafka.common.metrics.MetricsReporter
4. org.apache.kafka.common.security.oauthbearer.internals.expiring.ExpiringCredentialRefreshingLogin
5. org.apache.kafka.common.network.KafkaChannel
6. org.apache.kafka.clients.consumer.ConsumerInterceptor
7. org.apache.kafka.common.network.Selector.SelectorMetrics
8. org.apache.kafka.clients.consumer.internals.AbstractCoordinator.HeartbeatThread

Proposed Changes

Here are the proposed changesan example of how it would look like:

org.apache.kafka.streams.KafkaStreams

public class KafkaStreams implements AutoCloseable{
...
	public void close()
...
}

org.apache.kafka.streams.processor.internals.RecordCollectorImpl

public class RecordCollectorImpl implements RecordCollector, AutoCloseable {
...
}

org.apache.kafka.connect.runtime.ConnectMetrics.MetricGroup

public class MetricGroup implements AutoCloseable {
...
}

org.apache.kafka.connect.transforms.TimestampRouter

public class TimestampRouter<R extends ConnectRecord<R>> implements Transformation<R>, AutoCloseable {
...
}

org.apache.kafka.tools.VerifiableProducer

public class VerifiableProducer implements AutoCloseable {
...
}

Others changes are similar, will be added here later.

Compatibility, Deprecation, and Migration Plan

Compatibility, Deprecation, and Migration Plan

• This change will not have backward compatibility issues. It is legal to implement this AutoClosable interface without declaring "throws Exception" on close(), so the close() method signature won't be changed.  

Rejected Alternatives

• We decided not to choose Closeable(). Closeable extends AutoCloseable, and AutoCloseable throws a broader exception than Closeable,  so we think that AutoCloseable is a more generic and a more compatible option.N/A